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MONDO

MONDO:0023176 formaldehyde poisoning

Primary MONDO disease identifier for this formaldehyde poisoning entry.

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Definitions

1

Clinical case definition for formaldehyde poisoning

Formaldehyde poisoning is a toxic syndrome following inhalational, oral, or dermal and ocular exposure to formaldehyde or formalin, in which a highly reactive aldehyde damages the tissue of first contact by protein and nucleic acid crosslinking, with systemic acidosis and multiorgan failure when the dose is large enough to be absorbed.

CASE_DEFINITION Disease-level clinical framing across inhalational, ingestion, and chronic exposure routes

Show evidence (1 reference)

PMID:10962510 SUPPORT Other

"Formalin is irritating, corrosive and toxic and absorbed from all surfaces of the body."

Supports the core framing that formaldehyde is simultaneously an irritant and a corrosive, and is absorbed by every route of contact.

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Subtypes

3

Acute inhalational exposure (irritant syndrome)

Concentration-graded irritation of the eyes, nose, throat, and airways following formaldehyde vapour exposure, largely reversible on removal from exposure but capable of epithelial injury and pulmonary oedema at high concentration.

Show evidence (1 reference)

PMID:42101931 SUPPORT Human Clinical

"Controlled human chamber studies reported no measurable pulmonary impairment below 0.3 ppm, the onset of mild ocular and nasal irritation at 0.3 to 0.5 ppm, and reversible sensory irritation observed at concentrations approaching 1 ppm."

Establishes the concentration-graded irritant syndrome as the defining feature of the acute inhalational subtype, with reversibility at the doses that produce it.

Acute formalin ingestion (corrosive and systemic)

Swallowing of formalin, producing corrosive coagulative injury of the upper gastrointestinal tract together with systemic acidosis, shock, and multiorgan failure. Frequently fatal, and complicated by the methanol that stabilizes commercial formalin.

Show evidence (1 reference)

PMID:10962510 SUPPORT Human Clinical

"Ingestion can lead to immediate deleterious effects on almost all systems of the body including gastrointestinal tract, central nervous system, cardiovascular system and hepato-renal system, causing gastrointestinal hemorrhage, cardiovascular collapse, unconsciousness or convulsions, severe..."

Defines the ingestion subtype as a combined corrosive plus multisystem syndrome rather than a purely local injury.

Chronic occupational or environmental exposure

Repeated low-level inhalational or dermal exposure, producing sensitization, chronic airway and nasal mucosal changes, and - at the portal of entry - epithelial dysplasia and carcinoma risk.

Show evidence (1 reference)

PMID:32686516 SUPPORT Human Clinical

"Studies with humans gave evidence regarding significant deleterious effects on health associated to chronic FA occupational exposure."

Supports chronic occupational exposure as a distinct exposure subtype with documented human health effects.

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Mechanistic Hypotheses

3

Portal-of-entry local genotoxicity model

portal_of_entry_genotoxicity CANONICAL

Evidence balance 1 support

The dominant model: because formaldehyde is consumed by reaction within the first tissue it meets, genotoxic injury and the resulting carcinoma risk are confined to the site of contact. Stable-isotope work finds exogenous formaldehyde-DNA adducts only at the portal of entry, and the rodent bioassay finds tumours only in the nasal cavity and only at frankly cytotoxic concentrations. On this model carcinogenesis is a consequence of sustained local cytotoxicity plus regenerative proliferation, not of a cumulative systemic dose.

Pathograph links

Saturation of crosslink repair capacity -> Regenerative epithelial proliferation and dysplasia Unrepaired lesions are fixed as mutations in a proliferating epithelial field.

Regenerative epithelial proliferation and dysplasia -> Upper airway squamous cell carcinoma Mutations fixed in a chronically proliferating dysplastic field progress to carcinoma.

Show evidence (1 reference)

PMID:30701286 SUPPORT Model Organism

"Our data clearly show that endogenous adducts are present in all tissues analyzed, but exogenous adducts were not detectable in any tissue samples, including the most susceptible nasal epithelium."

Isotope-labelled inhalation shows exogenous adducts do not reach tissues distant from the portal of entry, which is the central argument for the local model.

Systemic haematopoietic genotoxicity model

systemic_haematopoietic_genotoxicity ALTERNATIVE

Evidence balance 1 support

The contested model behind the IARC myeloid-leukaemia classification: inhaled formaldehyde, or a transported reactive derivative, reaches haematopoietic stem cells and causes crosslink damage there. The epidemiology is mixed, the dosimetry is unexplained, and the animal leukaemia data come from genetic clearance failure (endogenous formaldehyde) rather than from inhalation - so this is curated as a competing model, not as settled pathophysiology.

Pathograph links

Saturation of crosslink repair capacity -> Haematopoietic stem cell genotoxic attrition Persistent crosslink damage in haematopoietic stem cells depletes the pool; demonstrated for endogenous formaldehyde in genetic models, and proposed but not established as a route from inhalational exposure.

Show evidence (1 reference)

PMID:24714728 SUPPORT Human Clinical

"it remains uncertain how inhaled formaldehyde might reach haematopoietic stem cells at sufficient concentrations to induce malignancy"

States the unresolved dosimetric objection to the systemic model, which is why this hypothesis is recorded as ALTERNATIVE rather than canonical.

Intravascular blood fixation model of circulatory collapse

intravascular_blood_fixation EMERGING

Evidence balance 1 support

A single forensic case proposes that rapid fixation of blood within the tissue, rather than shock secondary to mucosal injury and acidosis, is the proximate mechanism of death after formaldehyde ingestion. Recorded as an explicitly labelled emerging hypothesis so it is not mistaken for the conventional route.

Pathograph links

Protein coagulation and tissue fixation -> Acute circulatory collapse and multiorgan failure A proposed direct route in which intravascular fixation of blood precipitates acute circulatory failure; curated under an emerging hypothesis group, not as established mechanism.

Show evidence (1 reference)

PMID:35394178 SUPPORT Human Clinical

"we put forward a new viewpoint on the mechanism of death from formaldehyde poisoning in which formaldehyde causes rapid fixation of blood in the tissue, thus leading to acute circulatory disturbance"

The authors frame this as a new viewpoint they are proposing, which is why it is grouped as an emerging rather than canonical model.

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Discussions and Knowledge Gaps

5

Does inhaled formaldehyde reach haematopoietic stem cells in sufficient quantity to cause myeloid leukaemia in humans?

KNOWLEDGE GAP OPEN formaldehyde_leukaemia_route

Attached to

pathophysiology#Haematopoietic stem cell genotoxic attrition

IARC classifies formaldehyde as causing myeloid leukaemia, but the route is unexplained. Formaldehyde is consumed at the portal of entry; isotope-labelled inhalation finds no exogenous adducts at distant sites; no animal model reproduces leukaemia from inhalation; and large occupational cohorts disagree. The genetic models that do produce leukaemia do so through endogenous formaldehyde overload, which is a different exposure. Conflating the two is the most common error in this literature, so the systemic route is curated as an alternative hypothesis rather than as established mechanism.

Proposed experiments

Marrow adduct dosimetry at occupationally relevant formaldehyde concentrations

fa_marrow_adduct_dosimetry

Isotope-labelled formaldehyde inhalation at occupationally relevant peak concentrations, with adduct quantification in bone marrow rather than only at ambient concentrations.

ALDH2 rs671-stratified occupational cohort analysis

fa_aldh2_stratified_cohort

Occupational cohort analysis stratified by ALDH2 rs671 genotype, testing whether the clearance-deficient tail of the exposed population carries the excess risk if any exists.

Show evidence (1 reference)

PMID:24714728 SUPPORT Human Clinical

"it remains uncertain how inhaled formaldehyde might reach haematopoietic stem cells at sufficient concentrations to induce malignancy"

States the open dosimetric question that this discussion records.

Does the rodent nasal carcinogenicity bioassay translate to human upper airway cancer risk, given that the two species breathe differently and develop tumours at different sites?

HUMAN MODEL MISMATCH OPEN rodent_nasal_dosimetry_mismatch

Attached to

pathophysiology#Upper airway squamous cell carcinoma

Rats are obligate nose-breathers with high anterior nasal deposition and develop tumours there; humans are oronasal breathers and the epidemiological signal is nasopharyngeal. Mice, exposed identically, developed 2 tumours where rats developed 103, because they reflexively reduce minute ventilation on formaldehyde exposure. The mechanism transfers; the dosimetry may not, and the rat tumours arise only at frankly cytotoxic concentrations well above human occupational exposure. This is a translational validity question, not an absence of evidence.

Proposed experiments

Comparative human-rodent nasal dosimetry with site-specific adduct anchoring

fa_cfd_nasal_dosimetry

Computational fluid dynamics dosimetry of human versus rodent nasal and nasopharyngeal flux, anchored to measured site-specific adduct burden, to test whether the human nasopharyngeal tumour site corresponds to the region of highest human vapour flux.

Show evidence (1 reference)

PMID:6871871 SUPPORT Model Organism

"Squamous cell carcinomas were observed in the nasal cavities of 103 rats (52 females and 51 males) and 2 male mice exposed to 14.3 ppm and in 2 rats (one male and one female) exposed to 5.6 ppm of formaldehyde gas."

Quantifies the species disparity at identical exposure that motivates this mismatch discussion.

Does formaldehyde cause acute circulatory failure by fixing blood within the vasculature, as distinct from shock secondary to mucosal injury and acidosis?

EMERGING HYPOTHESIS OPEN intravascular_blood_fixation_mechanism

Attached to

pathophysiology#Protein coagulation and tissue fixation

A single forensic case report proposes that rapid intravascular fixation of blood, rather than the conventional route through mucosal injury and acidosis, is the proximate mechanism of death after formaldehyde ingestion. It is an interesting reading of the autopsy findings, but it is one case's hypothesis, and it is recorded here and grouped under an explicitly emerging hypothesis rather than presented as settled mechanism.

Show evidence (1 reference)

PMID:35394178 SUPPORT Human Clinical

"we put forward a new viewpoint on the mechanism of death from formaldehyde poisoning in which formaldehyde causes rapid fixation of blood in the tissue, thus leading to acute circulatory disturbance"

The authors frame this explicitly as a new viewpoint they are proposing, which is why it is curated as an emerging hypothesis rather than mechanism.

Are ALDH2 rs671 carriers a susceptible subpopulation for occupational formaldehyde exposure?

KNOWLEDGE GAP OPEN aldh2_rs671_exposure_interaction

Attached to

genetic#ALDH2

ALDH2*2 is dominant-negative and carried by a very large fraction of East Asian populations, and it demonstrably reduces formaldehyde tolerance in the inherited clearance-failure syndrome. Whether it modifies risk in formaldehyde-exposed workers has not, as far as this curation could establish, been characterized epidemiologically. This is a large, cheaply genotyped population and a testable prediction.

Proposed experiments

Genotype-stratified occupational surveillance in East Asian cohorts

fa_aldh2_genotype_surveillance

Genotype-stratified analysis of irritant symptoms, nasal cytology, and cancer incidence in East Asian formaldehyde-exposed occupational cohorts.

How should folate supplementation be weighed in formaldehyde poisoning, given that the folate backbone is itself a formaldehyde source?

OPEN QUESTION OPEN folate_paradox_in_formaldehyde_biology

Attached to

treatments#Folinic acid

Folinic acid is used to accelerate formate clearance, by analogy with methanol poisoning. Yet oxidation-prone folate derivatives decompose to formaldehyde, and folate supplementation kills cells that cannot detoxify it or repair its crosslinks. The acute high-formate patient and the chronically clearance-deficient cell are not the same situation, but the sign of the effect reverses between them, and no study addresses the acute-poisoning case directly.

Show evidence (1 reference)

PMID:28813411 SUPPORT In Vitro

"Notably, formaldehyde is generated from oxidative decomposition of the folate backbone."

Establishes the folate backbone as a formaldehyde source, which is the basis of the paradox this discussion records.

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Pathophysiology

17

Formaldehyde delivery at the portal of entry

Formaldehyde is small, highly water-soluble, and reacts essentially on contact, so the delivered dose is deposited and consumed in the first tissue it meets: the ocular surface and upper respiratory mucosa on inhalation, the oropharyngeal and gastric mucosa on ingestion, the epidermis on skin contact. More than 90% of inhaled formaldehyde is retained in the upper airway. This scrubbing at the portal of entry is the single organizing principle of the disease - it is why injury is concentration-driven rather than cumulative-dose-driven, and why the toxicology of a systemic route is so different from that of a local one.

respiratory tract epithelial cell CL:0002368

Downstream

Schiff-base adduction and methylene crosslinking of biomolecules Deposited formaldehyde reacts immediately with nucleophilic groups in the contacted tissue.

Trigeminal sensory irritation Formaldehyde at the mucosal surface stimulates trigeminal nerve endings.

Show evidence (2 references)

PMID:39828805 SUPPORT Human Clinical

"Retention of FA in the upper airways is > 90% in agreement with mice exposure studies that only extreme FA concentrations can surpass trachea, travel to the lower airways, and cause mild bronchoconstriction."

Quantifies upper-airway retention and states the corollary that only extreme concentrations reach beyond it, supporting portal-of-entry deposition.

PMID:42101931 SUPPORT Other

"inhalation was illustrated to follow a concentration-dependent continuum of effects confined to the tissues of initial contact"

States the portal-of-entry confinement principle directly. Tagged OTHER because this sentence is the review's synthesis across five decades of human, animal, and mechanistic studies rather than a single study type.

Schiff-base adduction and methylene crosslinking of biomolecules

The single chemical event underlying every arm of the disease. The aldehyde carbon is electrophilic and attacks nucleophilic sites - lysine epsilon-amino and N-terminal amines, cysteine thiols, and the exocyclic amines of DNA bases - forming methylol adducts that condense into stable methylene bridges. No metabolic activation is required. The same reaction that fixes a histology specimen denatures a gastric mucosa, haptenates a self protein, and crosslinks DNA to protein.

peptide cross-linking GO:0018149 ↑ INCREASED

Downstream

Protein coagulation and tissue fixation Crosslinked structural proteins lose their native conformation and function.

DNA-protein and interstrand crosslink formation Adduction of DNA bases and adjacent proteins produces covalent DNA lesions.

Haptenation and type IV sensitization Covalent modification of self proteins creates neoantigenic hapten-carrier complexes.

Show evidence (2 references)

PMID:40480196 SUPPORT Other

"It rapidly reacts with electron-rich groups in biomolecules like nucleic acids and proteins, leading to cellular damage."

States the shared electrophilic chemistry that produces both the protein and the nucleic acid arms of the injury.

PMID:30701286 SUPPORT Other

"The aldehyde moiety tends to react with nucleophilic sites in proteins and DNA, resulting in a number of DNA and protein adducts"

Specifies the aldehyde-nucleophile chemistry and the adduct products that follow from it.

Trigeminal sensory irritation

Formaldehyde at the ocular and upper-airway surface activates trigeminal nerve endings, triggering a reflex cascade of eyeblink, lacrimation, rhinorrhoea, and cough. This is the lowest-threshold effect of formaldehyde and the endpoint on which most occupational exposure limits are set. The early stages are fully reversible; sustained or high exposure carries the pathway into neurogenic inflammation and then tissue damage, which is where it converges with the cytotoxic arm.

inflammatory response GO:0006954 ↑ INCREASED

Downstream

Nasal and upper airway epithelial cytotoxicity Prolonged or high-concentration stimulation progresses from reversible reflex irritation to neurogenic inflammation and epithelial damage.

Show evidence (2 references)

PMID:25182421 SUPPORT Human Clinical

"pathway is initiated by the interaction of local irritants with receptors of the nervous system (e.g., trigeminal nerve endings) and a downstream cascade of reflexes and defense mechanisms (e.g., eyeblinks, coughing)"

Describes the sensory-irritation pathway that this node models, with formaldehyde as one of the three index substances in the analysis.

PMID:25182421 SUPPORT Human Clinical

"While the first stages of this pathway are thought to be completely reversible, high or prolonged exposure can lead to neurogenic inflammation and subsequently tissue damage."

Supports the reversibility of the early node and the downstream edge to epithelial injury at higher or sustained exposure.

Protein coagulation and tissue fixation

Extensive crosslinking of structural and enzymatic proteins denatures and coagulates them in situ. In the gastrointestinal tract after formalin ingestion this is visible at autopsy as literal tissue fixation - the mucosa and adjacent organs acquire the rigid, preserved morphology of a specimen. Coagulated cellular protein cannot carry out its normal function, so the tissue is killed rather than merely injured.

Intravascular blood fixation model of circulatory collapse

epithelial cell of alimentary canal CL:0002251

Downstream

Coagulative mucosal necrosis and ulceration Fixed, non-functional tissue undergoes coagulative necrosis with mucosal breakdown.

Acute circulatory collapse and multiorgan failure A proposed direct route in which intravascular fixation of blood precipitates acute circulatory failure; curated under an emerging hypothesis group, not as established mechanism.

Show evidence (2 references)

PMID:35394178 SUPPORT Human Clinical

"the mechanism of death from formaldehyde poisoning is that it rapidly causes coagulation of tissue cell protein, which may lose its normal function"

States protein coagulation with loss of function as the established mechanism of tissue injury after formaldehyde ingestion.

PMID:35394178 SUPPORT Human Clinical

"Anatomical examination revealed fixed tissue morphology of the stomach and adjacent organs."

Direct autopsy observation of in-situ tissue fixation in the stomach, grounding this node in a human finding rather than in analogy.

Coagulative mucosal necrosis and ulceration

Killed mucosa sloughs, producing ulceration, haemorrhage, and - with full-thickness injury - perforation and peritonitis. The stomach bears the worst of it after ingestion. Loss of the mucosal barrier is also the route by which formaldehyde and its metabolites enter the circulation in quantity.

Downstream

Systemic absorption and glutathione-dependent oxidation to formate A denuded, hyperaemic mucosal surface permits large-scale systemic absorption.

Fibrotic stricture formation Deep injury heals by granulation and fibrosis rather than by regeneration.

Show evidence (1 reference)

PMID:10962510 SUPPORT Human Clinical

"Ingestion can lead to immediate deleterious effects on almost all systems of the body including gastrointestinal tract, central nervous system, cardiovascular system and hepato-renal system, causing gastrointestinal hemorrhage, cardiovascular collapse, unconsciousness or convulsions, severe..."

Supports gastrointestinal haemorrhage as a consequence of the corrosive mucosal injury, alongside the systemic effects it precedes.

Fibrotic stricture formation

Corrosive injury that reaches beyond the mucosa does not regenerate; it heals by granulation and collagen deposition, and the scar contracts. Weeks after the acute episode this presents as oesophageal stricture and gastric outlet obstruction, often requiring repeated endoscopic dilation. This is the arm of the disease that persists in survivors, and it follows the conserved fibrotic-response pattern of injury to architectural distortion rather than anything formaldehyde-specific.

Downstream

Acute circulatory collapse and multiorgan failure Full-thickness necrosis progressing to perforation contributes to shock and multiorgan failure in the acute phase, before any fibrotic healing.

Show evidence (1 reference)

PMID:10962510 SUPPORT Human Clinical

"Formalin is irritating, corrosive and toxic and absorbed from all surfaces of the body."

Establishes the corrosive character of the injury that heals by fibrosis; it does not itself document stricture, so this is recorded as partial support.

Systemic absorption and glutathione-dependent oxidation to formate

Absorbed formaldehyde conjugates spontaneously with glutathione to S-hydroxymethylglutathione, which ADH5 (alcohol dehydrogenase 5, also called formaldehyde dehydrogenase or GSNOR) oxidizes to S-formylglutathione; hydrolysis then releases formate. ALDH2 provides a mitochondrial backup arm. This is a normal, high-capacity clearance route, not a bioactivation step - formaldehyde's blood half-life is very short and the pathway even feeds one-carbon metabolism. Toxicity is a capacity-overflow phenomenon: the problem is the size of the bolus, not the existence of the pathway. Note the contrast with methanol poisoning, where formaldehyde is the intermediate being made rather than the poison being cleared.

hepatocyte CL:0000182

formaldehyde catabolic process GO:0046294 ↑ INCREASED glutathione metabolic process GO:0006749 ↑ INCREASED

S-(hydroxymethyl)glutathione dehydrogenase activity GO:0051903 ↑ INCREASED

Experimental models

ADH5/ALDH2-deficient patient-derived iPSC haematopoietic differentiation IPSC DERIVED MODEL Human cells with graded clearance defects establish that ADH5 is the primary formaldehyde defence and ALDH2 the backup, which is the two-tier structure this node describes.

Animal models

Adh5-null Aldh2 E506K knock-in mouse Mouse perturbs Ablates both tiers of the formaldehyde clearance pathway modelled by this node, showing what happens when its capacity is removed entirely.

Downstream

Formate accumulation and high anion gap metabolic acidosis Formate produced faster than folate-dependent clearance can dispose of it accumulates.

Show evidence (3 references)

PMID:33355142 SUPPORT Other

"alcohol dehydrogenase 5 (also known as formaldehyde dehydrogenase or S-nitrosoglutathione reductase, ADH5/FDH/GSNOR) is the principal enzyme converting formaldehyde to formic acid in a glutathione-dependent manner"

Identifies ADH5 as the principal glutathione-dependent enzyme converting formaldehyde to formate, which is the chemistry of this node.

PMID:33512438 SUPPORT In Vitro

"We found that ADH5 is the primary defense against formaldehyde, and ALDH2 provides a backup."

Establishes the two-tier structure of the clearance pathway, with ADH5 primary and ALDH2 as the backup arm.

PMID:28813411 SUPPORT In Vitro

"Furthermore, we find that formaldehyde detoxification in human cells generates formate, and thereby promotes nucleotide synthesis."

Confirms formate as the product of human formaldehyde detoxification and supports the framing of this route as physiological rather than bioactivating.

Formate accumulation and high anion gap metabolic acidosis

Formate is eliminated slowly, by a saturable folate-dependent route, so a large formaldehyde load produces formate faster than it can be disposed of. Accumulated formate is an unmeasured anion and drives a severe high-anion-gap metabolic acidosis; it also inhibits mitochondrial cytochrome c oxidase, producing histotoxic hypoxia and lactate that widens the gap further. This is the same terminal chemistry as methanol poisoning, which matters clinically because commercial formalin is stabilized with methanol and the two toxidromes arrive together.

formate metabolic process GO:0015942 ↑ INCREASED

cytochrome-c oxidase activity GO:0004129 ↓ DECREASED

Downstream

Acute circulatory collapse and multiorgan failure Uncorrected severe acidosis and impaired oxidative phosphorylation precipitate shock and organ failure.

Show evidence (1 reference)

PMID:10962510 SUPPORT Human Clinical

"Ingestion can lead to immediate deleterious effects on almost all systems of the body including gastrointestinal tract, central nervous system, cardiovascular system and hepato-renal system, causing gastrointestinal hemorrhage, cardiovascular collapse, unconsciousness or convulsions, severe..."

Places severe metabolic acidosis among the immediate systemic consequences of formalin ingestion.

Acute circulatory collapse and multiorgan failure

The terminal common pathway of substantial ingestion: distributive and hypovolaemic shock from massive mucosal injury, compounded by refractory acidosis and histotoxic hypoxia, producing cardiovascular collapse, CNS depression, acute kidney injury, hepatic injury, and acute respiratory distress syndrome. Death typically follows within hours to days.

Show evidence (1 reference)

PMID:23640147 SUPPORT Human Clinical

"Despite proper supportive treatment in the absence of antidote, the infant died within 13 hours after deliberate poisoning."

Documents the fulminant multisystem course and the hours-scale time to death in a human case of formalin ingestion.

Nasal and upper airway epithelial cytotoxicity

Above the irritant threshold, formaldehyde kills the epithelium it contacts. In the chronic rodent inhalation bioassay this appears as rhinitis, epithelial dysplasia, and squamous metaplasia, strictly confined to the nasal cavity and proximal trachea and graded by concentration. There is a sharp transition rather than a smooth ramp: at or below about 2 ppm the changes are minimal and reversible, while at 6 ppm and above there is persistent epithelial necrosis.

nasopharyngeal epithelial cell CL:1001573

apoptotic process GO:0006915 ↑ INCREASED

Animal models

F344 rat two-year formaldehyde inhalation bioassay Rat recapitulates Reproduces concentration-graded rhinitis, epithelial dysplasia, and squamous metaplasia strictly confined to the nasal cavity and proximal trachea.

Downstream

Regenerative epithelial proliferation and dysplasia Sustained epithelial killing drives compensatory proliferation of the surviving basal population.

Show evidence (3 references)

PMID:6871871 SUPPORT Model Organism

"Significant formaldehyde-induced lesions were restricted to the nasal cavity and proximal trachea."

The strongest available demonstration that formaldehyde injury is confined to the portal of entry, from the canonical two-year inhalation bioassay.

PMID:6871871 SUPPORT Model Organism

"Rhinitis, epithelial dysplasia, and squamous metaplasia occurred in all exposure groups of rats and in the intermediate and high exposure groups of mice."

Documents the specific epithelial lesions modelled by this node and their concentration dependence.

PMID:42101931 SUPPORT Model Organism

"whereas exposures ≥6 ppm were associated with persistent epithelial necrosis, regenerative proliferation, and nasal squamous cell carcinomas localized to regions of highest vapor flux in the rat nasal cavity"

Gives the concentration threshold at which reversible adaptive change becomes sustained cytotoxic injury. The quoted finding is from the rat nasal cavity, hence MODEL_ORGANISM.

DNA-protein and interstrand crosslink formation

Formaldehyde reacting with DNA yields N2-hydroxymethyl-deoxyguanosine mono-adducts, DNA-DNA interstrand crosslinks, and - characteristically - covalent DNA-protein crosslinks. These lesions block replication fork progression and transcription, and they are the reason formaldehyde is genotoxic without requiring metabolic activation. This is also the point at which exogenous exposure joins a substantial endogenous background: formaldehyde is a normal product of histone and nucleic acid demethylation, so every cell already carries these adducts.

DNA damage response GO:0006974 ↑ INCREASED interstrand cross-link repair GO:0036297 ↑ INCREASED

Animal models

Adh5-null Fancd2-null mouse Mouse measures Direct mass-spectrometric quantification of formaldehyde-DNA adducts in tissue, showing that loss of ADH5 converts formaldehyde burden into DNA adduct burden.

Rat low-dose isotope-labelled formaldehyde inhalation Rat fails to recapitulate At environmentally relevant concentrations, inhaled formaldehyde produced no detectable exogenous adducts in any tissue - including the nasal epithelium - and did not change the endogenous adduct burden. The node is real, but low-dose inhalation does not reach it.

Downstream

Saturation of crosslink repair capacity Lesions accumulate faster than the crosslink repair machinery can resolve them.

Show evidence (2 references)

PMID:33355142 SUPPORT Other

"Aldehydes primarily produce DNA interstrand cross-links (ICL) and nonenzymatic DNA-protein cross-links (DPC)."

Names the two lesion classes this node models and their non-enzymatic origin.

PMID:26412304 SUPPORT Model Organism

"Endogenous formaldehyde is produced by numerous biochemical pathways fundamental to life, and it can crosslink both DNA and proteins."

Establishes both the crosslinking capability and the endogenous background against which exogenous exposure is superimposed.

Saturation of crosslink repair capacity

Formaldehyde-induced crosslinks are resolved by the Fanconi anaemia interstrand-crosslink pathway, with FANCD2 as a central node, and by DNA-protein-crosslink proteolysis. These systems have finite throughput. When the aldehyde burden outruns them, damage persists into replication - the injury is not a poisoned enzyme but an exceeded repair budget. This is the mechanistic hinge on which both the local carcinogenesis arm and the contested haematopoietic arm turn.

Portal-of-entry local genotoxicity model Systemic haematopoietic genotoxicity model

DNA repair GO:0006281 ↓ DECREASED

Downstream

Regenerative epithelial proliferation and dysplasia Unrepaired lesions are fixed as mutations in a proliferating epithelial field.

Haematopoietic stem cell genotoxic attrition Persistent crosslink damage in haematopoietic stem cells depletes the pool; demonstrated for endogenous formaldehyde in genetic models, and proposed but not established as a route from inhalational exposure.

Show evidence (2 references)

PMID:26412304 SUPPORT Model Organism

"The repair of this damage is mediated by FANCD2, a DNA crosslink repair protein."

Identifies the crosslink repair pathway that this node models as being saturable by formaldehyde damage.

PMID:33355142 SUPPORT Human Clinical

"our results suggest that the combined deficiency of formaldehyde clearance mechanisms leads to the complex clinical features due to overload of formaldehyde-induced DNA damage, thereby saturation of DNA repair processes"

States the capacity-overflow framing explicitly - disease follows when the formaldehyde burden saturates DNA repair.

Regenerative epithelial proliferation and dysplasia

Sustained cytotoxicity forces the surviving basal epithelium into continuous replacement proliferation. A proliferating field is exactly where unrepaired crosslink damage becomes fixed mutation, and the combination of chronic cell killing, regenerative division, and local genotoxicity is the accepted mode of action for formaldehyde's nasal carcinogenicity. Crucially, the non-neoplastic changes regress when exposure stops - it is only the carcinoma that does not.

Portal-of-entry local genotoxicity model

cell population proliferation GO:0008283 ↑ INCREASED

Downstream

Upper airway squamous cell carcinoma Mutations fixed in a chronically proliferating dysplastic field progress to carcinoma.

Show evidence (2 references)

PMID:42101931 SUPPORT Computational

"Computational dosimetry, DNA-protein crosslink kinetics, and biologically based dose-response (BBDR) modeling indicated that these outcomes arose from localized tissue injury rather than from cumulative systemic dose."

Supports localized cytotoxic injury with regenerative proliferation, not cumulative systemic dose, as the mode of action for the tumour outcome. The inference is drawn from dosimetry and BBDR modelling, hence COMPUTATIONAL.

PMID:6871871 SUPPORT Model Organism

"There was regression of rhinitis, dysplasia, and metaplasia at 27 months (3 months postexposure) in the 14.3- and 5.6-ppm groups of mice and in the 2.0- and 5.6-ppm groups of rats."

Demonstrates that the proliferative and dysplastic changes at this node are reversible on withdrawal of exposure, unlike the carcinoma downstream of them.

Upper airway squamous cell carcinoma

The best-anchored malignant endpoint. Squamous cell carcinoma arises at the site of maximal vapour flux - the anterior nasal cavity in the rat, the nasopharynx in exposed humans - and only in the setting of long-term exposure at concentrations that produce sustained cytotoxicity. Human epidemiology is not unanimous: the large NCI industrial cohort continues to show a nasopharyngeal cancer excess, while an equally large British chemical worker cohort found none.

nasopharyngeal epithelial cell CL:1001573

Animal models

F344 rat two-year formaldehyde inhalation bioassay Rat partially recapitulates Produces nasal squamous cell carcinoma, but only at concentrations that overwhelm local repair, and at an anatomical site that does not correspond to the human nasopharyngeal tumour location.

Show evidence (3 references)

PMID:6871871 SUPPORT Model Organism

"Squamous cell carcinomas were observed in the nasal cavities of 103 rats (52 females and 51 males) and 2 male mice exposed to 14.3 ppm and in 2 rats (one male and one female) exposed to 5.6 ppm of formaldehyde gas."

The primary animal demonstration of nasal squamous cell carcinoma, with the steep concentration dependence and the large species difference.

PMID:23788167 SUPPORT Human Clinical

"Consistent with previous analyses of this cohort, this update continues to suggest a link between formaldehyde exposure and nasopharyngeal cancer."

Human cohort support for the nasopharyngeal carcinoma endpoint, from the largest industrial cohort followed through 2004.

PMID:24714728 REFUTE Human Clinical

"Our results provide no support for an increased hazard of myeloid leukemia, nasopharyngeal carcinoma, or other upper airway tumors from formaldehyde exposure."

A comparably large human cohort finding no upper-airway cancer excess, recorded so the disagreement between the two cohorts is visible rather than resolved by selection.

Haematopoietic stem cell genotoxic attrition

Persistent formaldehyde-crosslink damage in haematopoietic stem cells impairs their differentiation and self-renewal and depletes the pool, ultimately producing marrow failure and leukaemic clonal evolution. This is firmly established for endogenous formaldehyde, in mice lacking clearance or repair and in humans with inherited clearance failure. Whether inhaled formaldehyde reaches the marrow in sufficient quantity to do the same is the contested question behind the IARC leukaemia classification, and is deliberately curated here under the alternative hypothesis rather than asserted.

hematopoietic stem cell CL:0000037

apoptotic process GO:0006915 ↑ INCREASED

Animal models

Adh5-null Fancd2-null mouse Mouse recapitulates Demonstrates that unrepaired formaldehyde crosslink damage depletes haematopoietic stem cells and precipitates bone marrow failure, with karyomegaly and dysfunction in liver and kidney as well.

Show evidence (3 references)

PMID:26412304 SUPPORT Model Organism

"Adh5(-/-)Fancd2(-/-) mice reveal an essential requirement for these protection mechanisms in hematopoietic stem cells (HSCs), leading to their depletion and precipitating bone marrow failure."

Demonstrates stem cell depletion and marrow failure from formaldehyde damage in a genetic mouse model; supports the mechanism, not the inhalational route.

PMID:33355142 SUPPORT Human Clinical

"Cellular studies revealed that a decrease in the formaldehyde tolerance underlies a loss of differentiation and proliferation capacity of hematopoietic stem cells."

Human cellular evidence that reduced formaldehyde tolerance costs haematopoietic stem cells their differentiation and proliferation capacity.

PMID:30701286 REFUTE Model Organism

"Moreover, formaldehyde exposure at 1, 30 and 300 ppb did not alter the levels of endogenous formaldehyde-induced DNA adducts or DNA-protein crosslinks."

Argues against low-dose inhaled formaldehyde reaching any tissue as genotoxic burden, which is the principal objection to reaching this node by the inhalational route.

Haptenation and type IV sensitization

Formaldehyde penetrating skin or airway epithelium covalently modifies self proteins, creating hapten-carrier complexes that dendritic cells take up and present. Hapten-specific T cells are primed, and on re-exposure mount a delayed-type hypersensitivity response - allergic contact dermatitis in skin. Sensitization is durable: it does not remit with exposure reduction, only with avoidance. Formaldehyde-releasing preservatives are a major and often unrecognized source, since a product need not list formaldehyde to deliver it.

dendritic cell CL:0000451 CD8-positive, alpha-beta T cell CL:0000625

inflammatory response GO:0006954 ↑ INCREASED

Show evidence (2 references)

PMID:18976378 SUPPORT Human Clinical

"Formaldehyde allergy is common and usually derives from formaldehyde-releasing biocides in cosmetic and other products."

Supports formaldehyde sensitization as a common clinical entity and names formaldehyde releasers as the usual source.

PMID:18976378 SUPPORT Human Clinical

"Reactions to formaldehyde-releasing compounds were seen in 79% of the formaldehyde-allergic patients."

Quantifies cross-reactivity to releasers among sensitized patients, supporting the shared haptenation mechanism.

Erythrocyte oxidant injury

A route-specific arm seen when formaldehyde reaches erythrocytes directly in the circulation rather than at a mucosal surface - classically iatrogenic contamination of dialysate, where residual formalin sterilant is delivered intravascularly. Formalin acts as a direct oxidant on red cells, producing acute intravascular haemolysis. The route matters: this does not follow from inhalational exposure.

response to oxidative stress GO:0006979 ↑ INCREASED

Show evidence (2 references)

PMID:6705281 SUPPORT Human Clinical

"A patient accidentally exposed to formalin during hemodialysis developed acute intravascular hemolysis."

Documents acute intravascular haemolysis after intravascular formalin exposure in a human patient.

PMID:6705281 SUPPORT In Vitro

"In vitro study showed that formalin has direct oxidant action on red blood cells."

Provides the mechanism for the haemolysis - direct oxidant action on erythrocytes rather than an immune process.

⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

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Phenotypes

23

Blood 2

Gastrointestinal hemorrhage HP:0002239

Temporal: ACUTE

Show evidence (1 reference)

PMID:10962510 SUPPORT Human Clinical

"Ingestion can lead to immediate deleterious effects on almost all systems of the body including gastrointestinal tract, central nervous system, cardiovascular system and hepato-renal system, causing gastrointestinal hemorrhage, cardiovascular collapse, unconsciousness or convulsions, severe..."

Names gastrointestinal haemorrhage explicitly among the immediate effects of formalin ingestion.

Acute intravascular hemolysis Hemolytic anemia HP:0001878

Temporal: ACUTE

Show evidence (1 reference)

PMID:6705281 SUPPORT Human Clinical

"A patient accidentally exposed to formalin during hemodialysis developed acute intravascular hemolysis."

Direct human documentation of acute intravascular haemolysis from intravascular formalin exposure.

Cardiovascular 2

Conjunctival irritation Conjunctivitis HP:0000509

Temporal: ACUTE

Show evidence (1 reference)

PMID:42101931 SUPPORT Human Clinical

"Controlled human chamber studies reported no measurable pulmonary impairment below 0.3 ppm, the onset of mild ocular and nasal irritation at 0.3 to 0.5 ppm, and reversible sensory irritation observed at concentrations approaching 1 ppm."

Controlled human exposure data placing ocular irritation at the lowest effect threshold for formaldehyde.

Circulatory shock HP:0031273

Temporal: ACUTE

Show evidence (1 reference)

PMID:10962510 SUPPORT Human Clinical

"Ingestion can lead to immediate deleterious effects on almost all systems of the body including gastrointestinal tract, central nervous system, cardiovascular system and hepato-renal system, causing gastrointestinal hemorrhage, cardiovascular collapse, unconsciousness or convulsions, severe..."

Names cardiovascular collapse explicitly among the immediate systemic effects of formalin ingestion.

Digestive 3

Vomiting HP:0002013

Temporal: ACUTE

Show evidence (1 reference)

PMID:10962510 SUPPORT Human Clinical

"Ingestion can lead to immediate deleterious effects on almost all systems of the body including gastrointestinal tract, central nervous system, cardiovascular system and hepato-renal system, causing gastrointestinal hemorrhage, cardiovascular collapse, unconsciousness or convulsions, severe..."

Supports immediate gastrointestinal injury after ingestion; vomiting itself is not named in the quoted text, so this is partial support.

Esophageal stricture HP:0002043

Course: PROGRESSIVE

Curated on the general corrosive-ingestion literature and the depth of formaldehyde mucosal injury; no formaldehyde-specific series quantifies stricture incidence, so no frequency band is recorded.

Show evidence (1 reference)

PMID:10962510 SUPPORT Human Clinical

"Formalin is irritating, corrosive and toxic and absorbed from all surfaces of the body."

Establishes the corrosive injury from which stricture follows; the source does not itself document stricture, so support is partial.

Dysphagia HP:0002015

Show evidence (1 reference)

PMID:10962510 SUPPORT Human Clinical

"Formalin is irritating, corrosive and toxic and absorbed from all surfaces of the body."

Supports corrosive injury of the swallowing passage; dysphagia is not named in the quoted text, so this is partial support.

Genitourinary 1

Acute kidney injury HP:0001919

Temporal: ACUTE

Show evidence (1 reference)

PMID:10962510 SUPPORT Human Clinical

"Ingestion can lead to immediate deleterious effects on almost all systems of the body including gastrointestinal tract, central nervous system, cardiovascular system and hepato-renal system, causing gastrointestinal hemorrhage, cardiovascular collapse, unconsciousness or convulsions, severe..."

Names hepato-renal system involvement among the immediate systemic effects of formalin ingestion.

Immune 1

Allergic contact dermatitis Eczematoid dermatitis HP:0000964

Temporal: RECURRENT

Deliberately carries no `frequency:` band. The best available number - a 2.88% pooled prevalence of formaldehyde contact allergy across 158 studies and over 1.3 million patients - has a denominator of *dermatitis patients undergoing patch testing*, not of formaldehyde-exposed people, so mapping it onto a FrequencyEnum band would silently change what the number means. It is recorded as evidence with its denominator stated instead. Regional variation is large (highest in North America at 6.8%), which is a further reason not to collapse it to a single band.

Show evidence (2 references)

PMID:18976378 SUPPORT Human Clinical

"The most common source of occupational sensitization was metalworking fluids followed by creams and related products."

Identifies the occupational sources of formaldehyde contact sensitization in a patch-test series.

PMID:42035787 SUPPORT Human Clinical

"The pooled prevalence of formaldehyde contact allergy was 2.88% (95% CI 2.55-3.24) with clinical relevance at 41.57%."

Quantifies formaldehyde contact allergy among dermatitis patients across 158 studies, establishing the phenotype as common and clinically relevant. The denominator is patch-tested dermatitis patients, not formaldehyde-exposed people, so it grounds the phenotype without supporting a frequency band.

Integument 1

Nasopharyngeal squamous cell carcinoma HP:0002860

Course: PROGRESSIVE

Show evidence (2 references)

PMID:23788167 SUPPORT Human Clinical

"With one additional death, previously observed excesses for nasopharyngeal cancer (n = 10) persisted for peak, average intensity and cumulative exposure"

Reports a persisting nasopharyngeal cancer excess with exposure gradient in the largest formaldehyde industrial cohort.

PMID:24714728 REFUTE Human Clinical

"Our results provide no support for an increased hazard of myeloid leukemia, nasopharyngeal carcinoma, or other upper airway tumors from formaldehyde exposure."

A second large cohort finding no nasopharyngeal carcinoma excess; retained so the disagreement between cohorts is explicit in the entry.

Metabolism 3

Acute respiratory distress syndrome Pulmonary edema HP:0100598

Temporal: ACUTE

Show evidence (1 reference)

PMID:10962510 SUPPORT Human Clinical

"Ingestion can lead to immediate deleterious effects on almost all systems of the body including gastrointestinal tract, central nervous system, cardiovascular system and hepato-renal system, causing gastrointestinal hemorrhage, cardiovascular collapse, unconsciousness or convulsions, severe..."

Names acute respiratory distress syndrome directly among the immediate effects of formalin ingestion.

High anion gap metabolic acidosis HP:0001942

Temporal: ACUTE Severity: SEVERE

Show evidence (1 reference)

PMID:10962510 SUPPORT Human Clinical

"Ingestion can lead to immediate deleterious effects on almost all systems of the body including gastrointestinal tract, central nervous system, cardiovascular system and hepato-renal system, causing gastrointestinal hemorrhage, cardiovascular collapse, unconsciousness or convulsions, severe..."

Names severe metabolic acidosis directly as an immediate consequence of formalin ingestion.

Elevated hepatic transaminases Elevated circulating hepatic transaminase concentration HP:0002910

Temporal: ACUTE

Show evidence (1 reference)

PMID:10962510 SUPPORT Human Clinical

"Ingestion can lead to immediate deleterious effects on almost all systems of the body including gastrointestinal tract, central nervous system, cardiovascular system and hepato-renal system, causing gastrointestinal hemorrhage, cardiovascular collapse, unconsciousness or convulsions, severe..."

Supports hepatic involvement; the quoted text does not report transaminase values, so support is partial.

Nervous System 2

Coma HP:0001259

Temporal: ACUTE

Show evidence (1 reference)

PMID:10962510 SUPPORT Human Clinical

"Ingestion can lead to immediate deleterious effects on almost all systems of the body including gastrointestinal tract, central nervous system, cardiovascular system and hepato-renal system, causing gastrointestinal hemorrhage, cardiovascular collapse, unconsciousness or convulsions, severe..."

Names unconsciousness among the immediate central nervous system effects of formalin ingestion.

Seizure HP:0001250

Temporal: ACUTE

Show evidence (1 reference)

PMID:10962510 SUPPORT Human Clinical

"Ingestion can lead to immediate deleterious effects on almost all systems of the body including gastrointestinal tract, central nervous system, cardiovascular system and hepato-renal system, causing gastrointestinal hemorrhage, cardiovascular collapse, unconsciousness or convulsions, severe..."

Names convulsions among the immediate central nervous system effects of formalin ingestion.

Respiratory 4

Cough HP:0012735

Temporal: ACUTE

Show evidence (1 reference)

PMID:25182421 SUPPORT Human Clinical

"pathway is initiated by the interaction of local irritants with receptors of the nervous system (e.g., trigeminal nerve endings) and a downstream cascade of reflexes and defense mechanisms (e.g., eyeblinks, coughing)"

Names coughing as part of the sensory-irritation reflex cascade for local irritants, of which formaldehyde is an index substance in this analysis.

Pharyngeal irritation Pharyngitis HP:0025439

Temporal: ACUTE

Show evidence (1 reference)

PMID:32686516 SUPPORT Human Clinical

"Evaluations carried out in experimental studies showed toxic effects on different organs as lung, upper respiratory tract, bone marrow and brain as well as in cells."

Supports upper respiratory tract as a target of formaldehyde toxicity; it does not name pharyngitis specifically, hence partial support.

Dyspnea HP:0002094

Show evidence (1 reference)

PMID:39828805 SUPPORT Human Clinical

"Retention of FA in the upper airways is > 90% in agreement with mice exposure studies that only extreme FA concentrations can surpass trachea, travel to the lower airways, and cause mild bronchoconstriction."

Supports lower-airway involvement only at extreme concentrations, which is the condition under which dyspnoea is expected; partial because the source argues against routine lower-airway effects.

Wheezing HP:0030828

Show evidence (1 reference)

PMID:39828805 SUPPORT Human Clinical

"Retention of FA in the upper airways is > 90% in agreement with mice exposure studies that only extreme FA concentrations can surpass trachea, travel to the lower airways, and cause mild bronchoconstriction."

Documents bronchoconstriction as an extreme-concentration effect; recorded as partial because the same review finds no lung-function impairment up to 4 ppm in controlled human studies.

Constitutional 1

Corrosive gastric injury Abdominal pain HP:0002027

Temporal: ACUTE

Show evidence (1 reference)

PMID:35394178 SUPPORT Human Clinical

"Anatomical examination revealed fixed tissue morphology of the stomach and adjacent organs."

Autopsy documentation of gastric tissue fixation as the corrosive lesion of formaldehyde ingestion.

Other 3

Nasal irritation and rhinitis HP:0012384

Show evidence (2 references)

PMID:42101931 SUPPORT Human Clinical

"Controlled human chamber studies reported no measurable pulmonary impairment below 0.3 ppm, the onset of mild ocular and nasal irritation at 0.3 to 0.5 ppm, and reversible sensory irritation observed at concentrations approaching 1 ppm."

Places nasal irritation alongside ocular irritation at the lowest human effect concentrations.

PMID:6871871 SUPPORT Model Organism

"Rhinitis, epithelial dysplasia, and squamous metaplasia occurred in all exposure groups of rats and in the intermediate and high exposure groups of mice."

Rodent inhalation data showing rhinitis at every exposure level; supporting, not sole, evidence for the human phenotype.

Asthma HP:0002099

Show evidence (1 reference)

PMID:39828805 REFUTE Human Clinical

"The evidence of a direct causal relationship between FA and asthma is insufficient from an experimental viewpoint that includes retention data in the upper airways and controlled animal and human exposure studies."

A review concluding that the causal formaldehyde-asthma link is not supported experimentally; recorded to keep the association honestly contested rather than asserted.

Myeloid leukemia HP:0012324

Show evidence (2 references)

PMID:24714728 REFUTE Human Clinical

"Our results provide no support for an increased hazard of myeloid leukemia, nasopharyngeal carcinoma, or other upper airway tumors from formaldehyde exposure."

Directly reports no excess myeloid leukaemia risk in a large exposed cohort, which is why this phenotype is curated as contested.

PMID:33147438 SUPPORT Model Organism

"We find that mice lacking two aldehyde detoxifying enzymes, mitochondrial ALDH2 and cytoplasmic ADH5, have greatly shortened lifespans and develop leukemia."

Shows formaldehyde can cause leukaemia when clearance fails genetically; partial because this is endogenous overload in a mouse, not inhalational exposure in a human.

🧬

Genetic Associations

3

ADH5

Gene: ADH5 hgnc:253 relationship_type: SUSCEPTIBILITY

Show evidence (2 references)

PMID:33512438 SUPPORT In Vitro

"We found that ADH5 is the primary defense against formaldehyde, and ALDH2 provides a backup."

Establishes ADH5 as the primary formaldehyde clearance enzyme, so its loss reduces the capacity that determines tolerance to a formaldehyde load.

PMID:26412304 SUPPORT Model Organism

"Here we show that endogenous formaldehyde is removed by the enzyme alcohol dehydrogenase 5 (ADH5/GSNOR), and Adh5(-/-) mice therefore accumulate formaldehyde adducts in DNA."

Demonstrates that losing ADH5 converts formaldehyde exposure into DNA adduct burden, the mechanistic basis for treating it as a susceptibility locus.

ALDH2

Gene: ALDH2 hgnc:404 relationship_type: SUSCEPTIBILITY

Show evidence (2 references)

PMID:33355142 SUPPORT Human Clinical

"ALDH2 detoxifies endogenous aldehydes, which are the major source of DNA damage repaired by the Fanconi anemia pathway."

Establishes ALDH2 as an aldehyde clearance enzyme whose failure shifts the burden onto DNA crosslink repair.

PMID:33147438 SUPPORT Model Organism

"We show that formaldehyde is a common substrate of ALDH2 and ADH5 and establish methods to quantify elevated blood formaldehyde and formaldehyde-DNA adducts in tissues."

Confirms formaldehyde as a shared substrate of both clearance enzymes, which is what makes ALDH2 a modifier of formaldehyde tolerance.

Variants (1)

ALDH2 rs671 (NM_000690.4:c.1510G>A, p.Glu504Lys)

The East Asian alcohol-flushing allele, also written ALDH2*2 and, in the mature protein numbering, E487K. It acts as a dominant negative on the ALDH2 tetramer, so heterozygotes lose most enzyme activity and carry reduced backup capacity for formaldehyde clearance.

Show evidence (1 reference)

PMID:33355142 SUPPORT Human Clinical

"Rs671 in the aldehyde dehydrogenase 2 gene (ALDH2) is the cause of Asian alcohol flushing response after drinking."

Identifies the rs671 allele and its population phenotype, in the paper that connects it to impaired formaldehyde clearance.

FANCD2

Gene: FANCD2 hgnc:3585 relationship_type: MODIFIER

Show evidence (1 reference)

PMID:26412304 SUPPORT Model Organism

"The repair of this damage is mediated by FANCD2, a DNA crosslink repair protein."

Identifies FANCD2 as the repair protein handling formaldehyde-induced DNA damage, the basis for treating it as a tolerance modifier.

💊

Medical Actions

8

Supportive multiorgan care

Action: supportive care Ontology label: Supportive Care NCIT:C15747

There is no antidote for formaldehyde. Management is supportive care of each affected organ system: airway protection with early intubation for laryngeal oedema, aggressive fluid resuscitation and vasopressors for shock, and ventilatory support. Emesis must not be induced and chemical neutralization must not be attempted - both re-expose the oesophagus, and neutralization is exothermic.

Mechanism Target:

MODULATES Acute circulatory collapse and multiorgan failure — Organ support sustains perfusion and gas exchange while the toxic insult is cleared; it does not act on the chemistry upstream of this node.

Show evidence (1 reference)

PMID:10962510 SUPPORT Human Clinical

"No specific antidote is available. Treatment of toxicity is supportive care of the various organ systems."

States directly that no antidote exists and that supportive organ care is the treatment.

Hemodialysis

Action: hemodialysis Ontology label: Hemodialysis NCIT:C15248

Extracorporeal removal is the key intervention in severe poisoning. It clears formate, corrects the acidosis, and simultaneously removes the methanol that stabilizes commercial formalin. The threshold for starting it should be low in a patient with severe high-anion-gap acidosis after formalin ingestion.

Mechanism Target:

INHIBITS Formate accumulation and high anion gap metabolic acidosis — Dialysis removes accumulated formate and corrects the acidosis it drives.

Sodium bicarbonate

Action: Pharmacotherapy NCIT:C15986

Agent: sodium bicarbonate CHEBI:32139

Intravenous sodium bicarbonate is given to correct the severe metabolic acidosis, buying time while formate is cleared. It treats the consequence, not the cause.

Mechanism Target:

MODULATES Formate accumulation and high anion gap metabolic acidosis — Buffering counteracts the acidaemia produced by accumulated formate without removing the formate itself.

Folinic acid

Action: Pharmacotherapy NCIT:C15986

Agent: folinic acid CHEBI:63606

Folinic acid supplies the reduced folate cofactor for 10-formyltetrahydrofolate dehydrogenase, the rate-limiting step in converting formate to carbon dioxide, and is used to accelerate formate clearance by analogy with methanol poisoning. Note a genuine paradox here: while folinic acid is standard acute therapy, folate derivatives are themselves a source of formaldehyde by oxidative decomposition of the folate backbone, and folate supplementation is cytotoxic to cells that cannot detoxify formaldehyde. The two situations are not the same, but the tension is worth knowing.

Mechanism Target:

INHIBITS Formate accumulation and high anion gap metabolic acidosis — Folinic acid accelerates folate-dependent oxidation of formate to carbon dioxide.

Show evidence (1 reference)

PMID:28813411 SUPPORT In Vitro

"Here we show that supplementation with tetrahydrofolate, the essential cofactor of this cycle, and other oxidation-prone folate derivatives kills human, mouse and chicken cells that cannot detoxify formaldehyde or that lack DNA crosslink repair."

Cited for the caveat rather than the indication: folate supplementation is cytotoxic in clearance-deficient cells, which qualifies the enthusiasm for folate rescue in this setting.

Fomepizole

Action: Pharmacotherapy NCIT:C15986

Agent: fomepizole CHEBI:5141

Fomepizole inhibits alcohol dehydrogenase and is indicated ONLY when there is significant methanol co-ingestion, which is common because commercial formalin is stabilized with 10-15% methanol. It does not treat formaldehyde itself: formaldehyde is already downstream of the alcohol dehydrogenase step, so blocking that enzyme does nothing to the formaldehyde already present. This distinction is easy to get backwards and matters clinically.

Removal from exposure

Action: Therapeutic Procedure NCIT:C49236

For the inhalational irritant syndrome and for occupational asthma and contact dermatitis, removal from exposure is the definitive intervention. The sensory irritation reflex arm is fully reversible in its early stages, and the non-neoplastic epithelial changes of chronic exposure regress once exposure stops - although carcinoma, once established, does not.

Mechanism Target:

INHIBITS Nasal and upper airway epithelial cytotoxicity — Ending exposure removes the driver of epithelial killing and permits regression of the non-neoplastic lesions.

Show evidence (1 reference)

PMID:6871871 SUPPORT Model Organism

"There was regression of rhinitis, dysplasia, and metaplasia at 27 months (3 months postexposure) in the 14.3- and 5.6-ppm groups of mice and in the 2.0- and 5.6-ppm groups of rats."

Demonstrates regression of the non-neoplastic epithelial lesions after exposure ends, which is the mechanistic basis for removal from exposure.

Bronchodilator therapy

Action: Pharmacotherapy NCIT:C15986

Agent: albuterol CHEBI:2549

Inhaled beta-2 agonists are used for bronchospasm after high-concentration inhalational exposure, alongside humidified oxygen and observation for delayed pulmonary oedema.

Endoscopic dilation of corrosive stricture

Action: endoscopic esophageal dilation Ontology label: Esophageal Dilation NCIT:C70908

Fibrotic oesophageal strictures and gastric outlet obstruction developing weeks after corrosive ingestion are managed with serial endoscopic balloon dilation; full-thickness necrosis or perforation requires emergency gastrectomy or oesophagectomy.

Mechanism Target:

RESTORES Fibrotic stricture formation — Mechanical dilation restores luminal calibre lost to fibrotic contraction.

🌍

Environmental Factors

5

Occupational formaldehyde vapour exposure

Anatomy, pathology and histology laboratories, embalming and funeral service, wood-composite manufacture using urea- and phenol-formaldehyde resins, textile finishing, healthcare disinfection, and hairdressing with keratin smoothing treatments are the principal occupational sources. This is the dominant population for chronic risk.

Show evidence (1 reference)

PMID:32686516 SUPPORT Human Clinical

"Studies with humans gave evidence regarding significant deleterious effects on health associated to chronic FA occupational exposure."

Supports chronic occupational exposure as a documented source of human health effects.

Mechanism Target:

TRIGGERS Formaldehyde delivery at the portal of entry — Inhaled formaldehyde vapour is deposited and consumed in the ocular surface and upper respiratory mucosa, which is where more than 90% of it is retained.

Show evidence (1 reference)

PMID:39828805 SUPPORT Human Clinical

"Retention of FA in the upper airways is > 90% in agreement with mice exposure studies that only extreme FA concentrations can surpass trachea, travel to the lower airways, and cause mild bronchoconstriction."

Quantifies the upper-airway retention that makes vapour exposure a portal-of-entry dose rather than a systemic one.

Ingestion of formalin solution

Swallowing of formalin, whether accidental from decanting into an unlabelled beverage container, self-inflicted, or homicidal. The alarming odour and immediate pain make this rare, and it is reported disproportionately from settings where formalin is domestically or industrially accessible.

Show evidence (2 references)

PMID:10962510 SUPPORT Human Clinical

"Ingestion is rare because of alarming odour and irritant effect but documented in accidental, homicidal or suicidal attempts."

Names the three documented intents behind formalin ingestion and explains why it is rare.

PMID:35394178 SUPPORT Human Clinical

"This article reports a case of a 50-year-old woman who died after accidentally drinking 25% formaldehyde solution in a transparent plastic bottle."

A documented accidental ingestion arising from decanting formalin into an unlabelled beverage container.

Mechanism Target:

TRIGGERS Formaldehyde delivery at the portal of entry — Swallowed formalin delivers a large formaldehyde dose directly onto the oropharyngeal and gastric mucosa, where it reacts on contact.

Show evidence (1 reference)

PMID:10962510 SUPPORT Human Clinical

"Formalin is irritating, corrosive and toxic and absorbed from all surfaces of the body."

Supports oral delivery producing both corrosive contact injury and systemic absorption.

Indoor air formaldehyde from building products and combustion

Off-gassing from pressed-wood furniture and building products, tobacco smoke, combustion, and formaldehyde-releasing consumer products maintain a domestic background exposure, higher in new or renovated interiors with poor ventilation and at higher temperature and humidity. Typical indoor concentrations sit below the sensory irritation threshold.

Show evidence (1 reference)

PMID:39828805 SUPPORT Human Clinical

"Formaldehyde (FA) is a ubiquitous indoor air pollutant emitted from construction, consumer, and combustion-related products, and ozone-initiated reactions with reactive organic volatiles."

Identifies the indoor sources of formaldehyde that constitute domestic background exposure.

Mechanism Target:

MODULATES Trigeminal sensory irritation — Indoor formaldehyde contributes to total inhaled dose and can approach the sensory irritation threshold in poorly ventilated settings; the cited review argues typical indoor concentrations sit well below it, so this is recorded as modulating rather than triggering.

Show evidence (1 reference)

PMID:39828805 SUPPORT Human Clinical

"Typical indoor FA concentrations in public buildings and homes are far below a threshold for sensory irritation in the upper airways, based on controlled human exposure studies, to induce sensory-irritative sensitization nor inflammatory epithelial damage in the airways."

States that typical indoor concentrations fall below the irritation threshold, which is why this exposure is curated as modulating total dose rather than as a trigger.

Iatrogenic intravascular formalin exposure during hemodialysis

Formalin is used to sterilize dialysis equipment, and residual sterilant reaching the extracorporeal circuit delivers formaldehyde straight into the bloodstream. This is the one route that bypasses the portal-of-entry scrubbing entirely, which is why it produces a haematological injury that inhalation does not.

Show evidence (1 reference)

PMID:6705281 SUPPORT Human Clinical

"Formalin intoxication should be recognized as a cause of acute hemolysis during hemodialysis and is not invariably fatal, provided further exposure is stopped in time and the complications prevented."

Identifies accidental formalin exposure during haemodialysis as a recognized exposure route, and notes it is survivable if exposure stops.

Mechanism Target:

TRIGGERS Erythrocyte oxidant injury — Formalin delivered into the extracorporeal blood circuit contacts erythrocytes directly and acts on them as an oxidant.

Show evidence (1 reference)

PMID:6705281 SUPPORT In Vitro

"In vitro study showed that formalin has direct oxidant action on red blood cells."

Establishes the direct oxidant action on erythrocytes that this exposure route triggers.

Dermal contact with formaldehyde and formaldehyde-releasing preservatives

Metalworking fluids, protective creams, detergents, liquid soaps, and cosmetics preserved with formaldehyde releasers such as quaternium-15 and DMDM hydantoin deliver repeated low-level skin exposure. A product need not declare formaldehyde to deliver it, which is why releaser allergy is often missed.

Show evidence (1 reference)

PMID:18976378 SUPPORT Human Clinical

"Exposure to formaldehyde-releasing preservatives in liquid soaps and other rinse-off products was common in both occupational and non-occupational cases."

Documents formaldehyde-releasing preservatives in everyday products as a common dermal exposure source.

Mechanism Target:

TRIGGERS Haptenation and type IV sensitization — Repeated skin contact allows formaldehyde to penetrate the epidermis and covalently modify self proteins, priming a hapten-specific T cell response.

Show evidence (1 reference)

PMID:18976378 SUPPORT Human Clinical

"The most common source of occupational sensitization was metalworking fluids followed by creams and related products."

Identifies the dermal exposures that produce documented occupational sensitization.

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Biochemical Markers

2

Serum formate (INCREASED)

Show evidence (1 reference)

PMID:28813411 SUPPORT In Vitro

"Furthermore, we find that formaldehyde detoxification in human cells generates formate, and thereby promotes nucleotide synthesis."

Establishes formate as the product of human formaldehyde detoxification, which is why it is the analyte that accumulates.

Post-mortem blood and tissue formaldehyde (INCREASED)

Show evidence (1 reference)

PMID:35394178 SUPPORT Human Clinical

"The toxicity test results showed that the concentrations of formaldehyde in the blood and gastric tissue were 36.56 mg/kg and 274.48 mg/kg, respectively"

Reports the measured post-mortem blood and gastric tissue concentrations used to establish formaldehyde poisoning as the cause of death.

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Diagnosis

3

Acid-base and osmolal gap workup

There is no useful clinical formaldehyde assay - blood formaldehyde is metabolized within minutes against a substantial endogenous background - so diagnosis rests on exposure history plus surrogate laboratory findings. Arterial blood gas and serum chemistry to establish a high anion gap is the diagnostic centrepiece after ingestion. An osmolal gap and a serum methanol level should be obtained alongside it, because commercial formalin is stabilized with methanol and a significant methanol co-ingestion changes management (it, and only it, is the indication for fomepizole).

arterial blood gas and anion gap measurement NCIT:C217391

Show evidence (1 reference)

PMID:10962510 SUPPORT Human Clinical

"Ingestion can lead to immediate deleterious effects on almost all systems of the body including gastrointestinal tract, central nervous system, cardiovascular system and hepato-renal system, causing gastrointestinal hemorrhage, cardiovascular collapse, unconsciousness or convulsions, severe..."

Establishes severe metabolic acidosis as an immediate and expected finding after formalin ingestion, which is what makes the acid-base workup the diagnostic centrepiece.

Upper gastrointestinal endoscopy with injury grading

Endoscopy within roughly 12-48 hours of a corrosive ingestion grades the depth of mucosal injury (conventionally by the Zargar scale) - early enough to grade, late enough for the injury to have declared itself, and before the tissue becomes friable enough that scoping risks perforation. The injury grade is the best available predictor of both stricture formation and mortality after corrosive ingestion, so it drives disposition and the intensity of stricture surveillance.

upper gastrointestinal endoscopy NCIT:C78144

Evidence here is from the general corrosive-ingestion literature rather than a formaldehyde-specific series; no formaldehyde-only endoscopic cohort was identified during this curation.

Show evidence (2 references)

PMID:31643028 SUPPORT Human Clinical

"High-grade esophageal mucosal injury was associated with a high risk of stricture formation (p = 0.02)."

Quantifies the prognostic value of the endoscopic injury grade for stricture formation, which is why endoscopic grading is the pivotal diagnostic step after corrosive ingestion.

PMID:31643028 SUPPORT Human Clinical

"There was no relationship between the presence of symptoms or oral mucosal injury and the grades of gastrointestinal mucosal injury."

Supports the need for endoscopy specifically: symptoms and visible oral burns do not predict the depth of gastrointestinal injury, so the grade cannot be inferred clinically. Partial because the cohort is corrosive ingestion generally, not formaldehyde alone.

Patch testing for formaldehyde and formaldehyde releasers

Suspected formaldehyde allergic contact dermatitis is confirmed by patch testing. Formaldehyde sits in most baseline series, but the releasers must be tested separately - a product need not declare formaldehyde to deliver it, and a negative formaldehyde patch does not exclude releaser allergy.

patch testing NCIT:C17137

Show evidence (2 references)

PMID:18976378 SUPPORT Human Clinical

"Between January 2001 and May 2007, we had patch tested 81 patients with formaldehyde allergy and 18 with independent allergy to some formaldehyde releaser."

Documents patch testing as the diagnostic method in practice, and shows that releaser allergy occurs independently of formaldehyde allergy - the reason both are tested.

PMID:42035787 SUPPORT Human Clinical

"The pooled prevalence of formaldehyde contact allergy was 2.88% (95% CI 2.55-3.24) with clinical relevance at 41.57%."

Gives the diagnostic yield of patch testing in the population it is actually applied to - dermatitis patients under investigation - pooled across 158 studies and over 1.3 million patients.

📊

Prevalence

1

Worldwide

Unknown Not yet documented

No reliable incidence or prevalence figures exist for formaldehyde poisoning as such. It is not a reportable condition and poison-centre aggregate data do not break it out cleanly; the acute literature is almost entirely case reports and small series. Ingestion in particular is self-limiting at the point of exposure because of the smell and immediate pain, which is why it is reported mainly as accidental decanting, self-harm, or homicide.

Show evidence (1 reference)

PMID:23640147 SUPPORT Human Clinical

"Acute poisoning of formalin is rare because of its strong irritating effect and alarming odor."

Supports the rarity of acute formalin poisoning and names the reason for it, without asserting a rate the literature cannot provide.

🔀

Differential Diagnoses

3

Conditions with similar clinical presentations that must be differentiated from Formaldehyde Poisoning:

Methanol poisoning MONDO:0017860

Overlapping Features The most important differential and also the most common co-diagnosis. In methanol poisoning formaldehyde is the transient intermediate being produced; in formaldehyde poisoning it is the poison being cleared. Both converge on formate.

Distinguishing Features

Shares formate accumulation, high-anion-gap acidosis, and visual loss, but lacks corrosive gastrointestinal injury
Distinguished by an elevated osmolal gap and detectable serum methanol
Frequently coexists, because commercial formalin is stabilized with 10-15% methanol
Fomepizole is indicated for methanol and useless against formaldehyde already formed

Acid or alkali caustic ingestion

Overlapping Features Other caustic ingestions produce a similar corrosive picture but do not carry the systemic formate load, so the depth of acidosis is the discriminator.

Distinguishing Features

Corrosive gastrointestinal injury without the disproportionate systemic acidosis of formalin
Alkali produces deeper liquefactive oesophageal injury; formaldehyde produces coagulative fixation

ADH5/ALDH2 deficiency (AMeD syndrome)

Overlapping Features The inherited mirror image of this entry: the same molecule, no exposure at all, because the drain is blocked rather than the tap left running. It is a separate disease entity and is not curated here, but it is the mechanistic anchor for the genotoxic arm of formaldehyde biology.

Distinguishing Features

No exogenous exposure; disease arises from failure to clear endogenous formaldehyde
Childhood onset with aplastic anaemia, short stature, and intellectual disability
Digenic - biallelic ADH5 variants plus the heterozygous ALDH2 rs671 allele
Chromosome fragility testing is negative, distinguishing it from Fanconi anaemia

Show evidence (1 reference)

PMID:38614309 SUPPORT Human Clinical

"ADH5/ALDH2 deficiency is a rare inherited syndrome characterized by short stature, microcephaly, delayed mental development, and hematopoietic dysfunction and has recently been proposed as a disease paradigm."

Defines the inherited clearance-failure syndrome and its clinical triad, which is what distinguishes it from exposure-driven formaldehyde poisoning.

🧫

Experimental Models

1

ADH5/ALDH2-deficient patient-derived iPSC haematopoietic differentiation IPSC_DERIVED_MODEL

Induced pluripotent stem cells from patients with biallelic ADH5 variants plus a heterozygous ALDH2*2 allele, differentiated toward haematopoiesis, used to establish the hierarchy of the two clearance enzymes in a human genetic background.

Publication

PMID:33512438

Pathograph links

Systemic absorption and glutathione-dependent oxidation to formate perturbs fidelity: high Human cells with graded clearance defects establish that ADH5 is the primary formaldehyde defence and ALDH2 the backup, which is the two-tier structure this node describes.

Limitations: An in vitro differentiation system driven by endogenous formaldehyde, not a model of exogenous exposure; it speaks to clearance capacity rather than to the toxicology of a swallowed or inhaled dose.

Readouts

Spontaneous sister chromatid exchange in patient lymphocytes

Direction: INCREASED

Interpretation: A cellular readout that clearance failure translates into recombinational repair of formaldehyde damage; notably cell-type dependent, since patient fibroblasts were normal.

Show evidence (1 reference)

PMID:33512438 SUPPORT Human Clinical

"Phytohemagglutinin-stimulated lymphocytes from these patients displayed highly increased numbers of spontaneous sister chromatid exchanges (SCEs), reflecting homologous recombination repair of formaldehyde damage."

Reports the sister chromatid exchange measurement behind this readout.

Show evidence (1 reference)

PMID:33512438 SUPPORT In Vitro

"We found that ADH5 is the primary defense against formaldehyde, and ALDH2 provides a backup."

Supports the model as informative for the structure of the clearance pathway at this node.

🐁

Animal Models

4

F344 rat two-year formaldehyde inhalation bioassay

The canonical carcinogenicity model: 0, 2.0, 5.6, and 14.3 ppm formaldehyde gas, 6 h/day, 5 days/week for 24 months, with up to 6 months of follow-up after exposure ended. It established both the portal-of-entry confinement of injury and the steep concentration dependence of the tumour response.

Species

Rat

Genotype

Wild-type Fischer 344

Publication

PMID:6871871

Pathograph links

Nasal and upper airway epithelial cytotoxicity recapitulates fidelity: high Reproduces concentration-graded rhinitis, epithelial dysplasia, and squamous metaplasia strictly confined to the nasal cavity and proximal trachea.

Limitations: Rats are obligate nose-breathers with high nasal deposition, whereas humans are oronasal breathers; the rat lesion is anterior nasal while human tumours cluster at the nasopharynx, so the anatomical site does not transfer directly.

Readouts

Nasal epithelial dysplasia and squamous metaplasia

Direction: INCREASED

Interpretation: Histological correlate of the epithelial cytotoxicity node in this model.

Show evidence (1 reference)

PMID:6871871 SUPPORT Model Organism

"Rhinitis, epithelial dysplasia, and squamous metaplasia occurred in all exposure groups of rats and in the intermediate and high exposure groups of mice."

Reports the histological measurement behind this readout.

Regression of non-neoplastic lesions after exposure ends

Direction: RESTORED

Interpretation: Establishes that this node is reversible, unlike the carcinoma downstream of it.

Show evidence (1 reference)

PMID:6871871 SUPPORT Model Organism

"There was regression of rhinitis, dysplasia, and metaplasia at 27 months (3 months postexposure) in the 14.3- and 5.6-ppm groups of mice and in the 2.0- and 5.6-ppm groups of rats."

Reports the post-exposure regression measurement behind this readout.

Show evidence (1 reference)

PMID:6871871 SUPPORT Model Organism

"Significant formaldehyde-induced lesions were restricted to the nasal cavity and proximal trachea."

Supports treating this bioassay as informative for portal-of-entry epithelial injury.

Upper airway squamous cell carcinoma partially recapitulates fidelity: moderate Produces nasal squamous cell carcinoma, but only at concentrations that overwhelm local repair, and at an anatomical site that does not correspond to the human nasopharyngeal tumour location.

Limitations: Tumours arose only at 5.6 and 14.3 ppm, far above human occupational exposure, and the near-total absence of tumours in mice at the same concentrations shows the response is governed by species-specific nasal dosimetry rather than by a species-invariant dose-response.

Readouts

Nasal squamous cell carcinoma incidence

Direction: INCREASED

Interpretation: The tumour endpoint of the bioassay, with its species and concentration dependence.

Show evidence (1 reference)

PMID:6871871 SUPPORT Model Organism

"Squamous cell carcinomas were observed in the nasal cavities of 103 rats (52 females and 51 males) and 2 male mice exposed to 14.3 ppm and in 2 rats (one male and one female) exposed to 5.6 ppm of formaldehyde gas."

Reports the tumour counts by species and concentration behind this readout.

Show evidence (1 reference)

PMID:6871871 SUPPORT Model Organism

"Squamous cell carcinomas were observed in the nasal cavities of 103 rats (52 females and 51 males) and 2 male mice exposed to 14.3 ppm and in 2 rats (one male and one female) exposed to 5.6 ppm of formaldehyde gas."

Supports the model as informative for formaldehyde carcinogenesis while showing the species disparity that limits direct human extrapolation.

Adh5-null Fancd2-null mouse

Combined loss of formaldehyde clearance and crosslink repair, which turns endogenous formaldehyde into a lethal genotoxin. The reference model for the genotoxic arm of formaldehyde biology.

Species

Mouse

Genotype

Adh5-/- Fancd2-/-

Publication

PMID:26412304

Pathograph links

Haematopoietic stem cell genotoxic attrition recapitulates fidelity: high Demonstrates that unrepaired formaldehyde crosslink damage depletes haematopoietic stem cells and precipitates bone marrow failure, with karyomegaly and dysfunction in liver and kidney as well.

Limitations: This is endogenous formaldehyde overload created by genetic ablation of clearance and repair, not inhalational exposure. It establishes that formaldehyde can do this to stem cells; it does not establish that inhaled formaldehyde reaches them.

Readouts

Haematopoietic stem cell depletion and marrow failure

Direction: DECREASED

Interpretation: Functional correlate of stem cell attrition in this model.

Show evidence (1 reference)

PMID:26412304 SUPPORT Model Organism

"Adh5(-/-)Fancd2(-/-) mice reveal an essential requirement for these protection mechanisms in hematopoietic stem cells (HSCs), leading to their depletion and precipitating bone marrow failure."

Reports the stem cell depletion measurement behind this readout.

Show evidence (1 reference)

PMID:26412304 SUPPORT Model Organism

"Formaldehyde is therefore an important source of endogenous DNA damage that is counteracted in mammals by a conserved protection mechanism."

Supports treating this model as informative for the formaldehyde genotoxicity node.

DNA-protein and interstrand crosslink formation measures fidelity: high Direct mass-spectrometric quantification of formaldehyde-DNA adducts in tissue, showing that loss of ADH5 converts formaldehyde burden into DNA adduct burden.

Readouts

Formaldehyde-DNA adduct accumulation in tissue

Direction: INCREASED

Interpretation: Molecular correlate of the adduct and crosslink node in this model.

Show evidence (1 reference)

PMID:26412304 SUPPORT Model Organism

"Here we show that endogenous formaldehyde is removed by the enzyme alcohol dehydrogenase 5 (ADH5/GSNOR), and Adh5(-/-) mice therefore accumulate formaldehyde adducts in DNA."

Reports the adduct measurement behind this readout.

Adh5-null Aldh2 E506K knock-in mouse

A genocopy of the two-tier human clearance failure, with the mouse equivalent of the human ALDH2 p.Glu504Lys allele on an Adh5-null background.

Species

Mouse

Genotype

Adh5-/- Aldh2 E506K/E506K

Publication

PMID:33355142

Pathograph links

Systemic absorption and glutathione-dependent oxidation to formate perturbs fidelity: high Ablates both tiers of the formaldehyde clearance pathway modelled by this node, showing what happens when its capacity is removed entirely.

Limitations: Models loss of clearance capacity rather than an exogenous formaldehyde load, and produces a developmental and haematopoietic syndrome that is not the phenotype of acute formaldehyde poisoning.

Show evidence (1 reference)

PMID:33355142 SUPPORT Model Organism

"Moreover, Adh5-/-Aldh2 E506K/E506K double-deficient mice recapitulated key clinical features of AMeDS, showing short life span, dwarfism, and hematopoietic failure."

Supports the model as a faithful genetic ablation of the clearance pathway this node describes.

Rat low-dose isotope-labelled formaldehyde inhalation

Nose-only inhalation of isotope-labelled formaldehyde at 1, 30, and 300 ppb for 28 days, with mass-spectrometric discrimination of exogenous from endogenous DNA adducts and DNA-protein crosslinks. Designed to answer whether inhaled formaldehyde contributes measurable genotoxic burden at ambient concentrations.

Species

Rat

Genotype

Wild-type

Publication

PMID:30701286

Pathograph links

DNA-protein and interstrand crosslink formation fails to recapitulate fidelity: high At environmentally relevant concentrations, inhaled formaldehyde produced no detectable exogenous adducts in any tissue - including the nasal epithelium - and did not change the endogenous adduct burden. The node is real, but low-dose inhalation does not reach it.

Limitations: Tested only up to 300 ppb, far below the concentrations at which the rodent bioassay produces tumours, so this is a statement about ambient exposure rather than about occupational peaks or the rat carcinogenicity range.

Readouts

Exogenous formaldehyde-DNA adducts and DNA-protein crosslinks

Direction: UNCHANGED

Interpretation: A negative result at ambient concentrations, and the load-bearing evidence for the portal-of-entry hypothesis.

Show evidence (1 reference)

PMID:30701286 SUPPORT Model Organism

"Moreover, formaldehyde exposure at 1, 30 and 300 ppb did not alter the levels of endogenous formaldehyde-induced DNA adducts or DNA-protein crosslinks."

Reports the negative adduct measurement behind this readout.

Show evidence (1 reference)

PMID:30701286 SUPPORT Model Organism

"Our data clearly show that endogenous adducts are present in all tissues analyzed, but exogenous adducts were not detectable in any tissue samples, including the most susceptible nasal epithelium."

Substantiates the negative claim that low-dose inhalation does not add to the genotoxic burden at this node.

{ }

Source YAML

click to show

name: Formaldehyde Poisoning
creation_date: "2026-08-13T00:00:00Z"
category: Environmental
categories:
- Toxic Exposure Disorder
- Aldehyde Toxicity
- Environmental Health Disorder
- Occupational Disease
synonyms:
- formalin poisoning
- formalin intoxication
- formaldehyde toxicity
- formaldehyde intoxication
- methanal poisoning
description: >-
  Formaldehyde poisoning is the toxic effect of exposure to formaldehyde gas,
  aqueous formaldehyde (formalin, typically a 37-40% solution stabilized with
  10-15% methanol), or formaldehyde-releasing agents. Formaldehyde is a small,
  highly water-soluble, highly reactive electrophilic aldehyde that forms
  Schiff-base adducts and methylene crosslinks with the amine and thiol groups
  of proteins and nucleic acids. Because it reacts so fast, its injury is
  largely confined to the tissue of first contact, and the clinical syndrome is
  set by route and dose rather than by a single downstream pathway. Inhalation
  produces a concentration-graded irritant syndrome of the eyes and upper
  airway, with epithelial cytotoxicity and regenerative proliferation at higher
  concentrations. Ingestion of formalin produces corrosive coagulative necrosis
  of the upper gastrointestinal tract - the same protein fixation that preserves
  a specimen jar - followed by systemic absorption, formate accumulation, severe
  high-anion-gap metabolic acidosis, circulatory collapse, and multiorgan
  failure; survivors may develop fibrotic strictures weeks later. Repeated
  contact causes haptenation and type IV sensitization (allergic contact
  dermatitis). Chronic inhalation is linked to upper-airway carcinoma, and
  formaldehyde is classified by IARC as a human carcinogen, though the
  mechanistic route to distant-site haematopoietic malignancy remains contested.
  There is no antidote; management is supportive, with hemodialysis for formate
  and acidosis, and fomepizole reserved for significant methanol co-ingestion.
disease_term:
  preferred_term: formaldehyde poisoning
  term:
    id: MONDO:0023176
    label: formaldehyde poisoning
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0023176
      label: formaldehyde poisoning
    mapping_predicate: skos:exactMatch
    mapping_source: MONDO
    mapping_justification: Primary MONDO disease identifier for this formaldehyde poisoning entry.
definitions:
- name: Clinical case definition for formaldehyde poisoning
  definition_type: CASE_DEFINITION
  description: >-
    Formaldehyde poisoning is a toxic syndrome following inhalational, oral, or
    dermal and ocular exposure to formaldehyde or formalin, in which a highly
    reactive aldehyde damages the tissue of first contact by protein and nucleic
    acid crosslinking, with systemic acidosis and multiorgan failure when the
    dose is large enough to be absorbed.
  scope: Disease-level clinical framing across inhalational, ingestion, and chronic exposure routes
  evidence:
  - reference: PMID:10962510
    reference_title: "Toxicity of ingested formalin and its management."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Formalin is irritating, corrosive and toxic and absorbed from all surfaces of the body."
    explanation: >-
      Supports the core framing that formaldehyde is simultaneously an irritant
      and a corrosive, and is absorbed by every route of contact.
parents:
- chemical poisoning
- aldehyde poisoning
has_subtypes:
- name: Acute inhalation
  display_name: Acute inhalational exposure (irritant syndrome)
  description: >-
    Concentration-graded irritation of the eyes, nose, throat, and airways
    following formaldehyde vapour exposure, largely reversible on removal from
    exposure but capable of epithelial injury and pulmonary oedema at high
    concentration.
  evidence:
  - reference: PMID:42101931
    reference_title: "The formaldehyde dispute - Part A: acute and chronic inhalation toxicity and the evolution of scientific knowledge."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Controlled human chamber studies reported no measurable pulmonary impairment below 0.3 ppm, the onset of mild ocular and nasal irritation at 0.3 to 0.5 ppm, and reversible sensory irritation observed at concentrations approaching 1 ppm."
    explanation: >-
      Establishes the concentration-graded irritant syndrome as the defining
      feature of the acute inhalational subtype, with reversibility at the doses
      that produce it.
- name: Acute ingestion
  display_name: Acute formalin ingestion (corrosive and systemic)
  description: >-
    Swallowing of formalin, producing corrosive coagulative injury of the upper
    gastrointestinal tract together with systemic acidosis, shock, and
    multiorgan failure. Frequently fatal, and complicated by the methanol that
    stabilizes commercial formalin.
  evidence:
  - reference: PMID:10962510
    reference_title: "Toxicity of ingested formalin and its management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Ingestion can lead to immediate deleterious effects on almost all systems of the body including gastrointestinal tract, central nervous system, cardiovascular system and hepato-renal system, causing gastrointestinal hemorrhage, cardiovascular collapse, unconsciousness or convulsions, severe metabolic acidosis and acute respiratory distress syndrome."
    explanation: >-
      Defines the ingestion subtype as a combined corrosive plus multisystem
      syndrome rather than a purely local injury.
- name: Chronic exposure
  display_name: Chronic occupational or environmental exposure
  description: >-
    Repeated low-level inhalational or dermal exposure, producing sensitization,
    chronic airway and nasal mucosal changes, and - at the portal of entry -
    epithelial dysplasia and carcinoma risk.
  evidence:
  - reference: PMID:32686516
    reference_title: "Formaldehyde toxicity reports from in vitro and in vivo studies: a review and updated data."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Studies with humans gave evidence regarding significant deleterious effects on health associated to chronic FA occupational exposure."
    explanation: >-
      Supports chronic occupational exposure as a distinct exposure subtype with
      documented human health effects.
prevalence:
- population: Worldwide
  measure_type: UNKNOWN
  prevalence_class: NOT_YET_DOCUMENTED
  notes: >-
    No reliable incidence or prevalence figures exist for formaldehyde poisoning
    as such. It is not a reportable condition and poison-centre aggregate data
    do not break it out cleanly; the acute literature is almost entirely case
    reports and small series. Ingestion in particular is self-limiting at the
    point of exposure because of the smell and immediate pain, which is why it
    is reported mainly as accidental decanting, self-harm, or homicide.
  evidence:
  - reference: PMID:23640147
    reference_title: "Homicidal acute formalin poisoning in an infant from a rural sericulture family presenting with multisystem failure."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Acute poisoning of formalin is rare because of its strong irritating effect and alarming odor."
    explanation: >-
      Supports the rarity of acute formalin poisoning and names the reason for
      it, without asserting a rate the literature cannot provide.
mechanistic_hypotheses:
- hypothesis_group_id: portal_of_entry_genotoxicity
  hypothesis_label: Portal-of-entry local genotoxicity model
  status: CANONICAL
  description: >-
    The dominant model: because formaldehyde is consumed by reaction within the
    first tissue it meets, genotoxic injury and the resulting carcinoma risk are
    confined to the site of contact. Stable-isotope work finds exogenous
    formaldehyde-DNA adducts only at the portal of entry, and the rodent
    bioassay finds tumours only in the nasal cavity and only at frankly
    cytotoxic concentrations. On this model carcinogenesis is a consequence of
    sustained local cytotoxicity plus regenerative proliferation, not of a
    cumulative systemic dose.
  evidence:
  - reference: PMID:30701286
    reference_title: "Evaluation of inhaled low-dose formaldehyde-induced DNA adducts and DNA-protein cross-links by liquid chromatography-tandem mass spectrometry."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Our data clearly show that endogenous adducts are present in all tissues analyzed, but exogenous adducts were not detectable in any tissue samples, including the most susceptible nasal epithelium."
    explanation: >-
      Isotope-labelled inhalation shows exogenous adducts do not reach tissues
      distant from the portal of entry, which is the central argument for the
      local model.
- hypothesis_group_id: systemic_haematopoietic_genotoxicity
  hypothesis_label: Systemic haematopoietic genotoxicity model
  status: ALTERNATIVE
  description: >-
    The contested model behind the IARC myeloid-leukaemia classification:
    inhaled formaldehyde, or a transported reactive derivative, reaches
    haematopoietic stem cells and causes crosslink damage there. The
    epidemiology is mixed, the dosimetry is unexplained, and the animal
    leukaemia data come from genetic clearance failure (endogenous formaldehyde)
    rather than from inhalation - so this is curated as a competing model, not
    as settled pathophysiology.
  evidence:
  - reference: PMID:24714728
    reference_title: "Upper airway cancer, myeloid leukemia, and other cancers in a cohort of British chemical workers exposed to formaldehyde."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "it remains uncertain how inhaled formaldehyde might reach haematopoietic stem cells at sufficient concentrations to induce malignancy"
    explanation: >-
      States the unresolved dosimetric objection to the systemic model, which is
      why this hypothesis is recorded as ALTERNATIVE rather than canonical.
- hypothesis_group_id: intravascular_blood_fixation
  hypothesis_label: Intravascular blood fixation model of circulatory collapse
  status: EMERGING
  description: >-
    A single forensic case proposes that rapid fixation of blood within the
    tissue, rather than shock secondary to mucosal injury and acidosis, is the
    proximate mechanism of death after formaldehyde ingestion. Recorded as an
    explicitly labelled emerging hypothesis so it is not mistaken for the
    conventional route.
  evidence:
  - reference: PMID:35394178
    reference_title: "A fatal case of accidental oral formaldehyde poisoning and its pathomorphological characteristics."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we put forward a new viewpoint on the mechanism of death from formaldehyde poisoning in which formaldehyde causes rapid fixation of blood in the tissue, thus leading to acute circulatory disturbance"
    explanation: >-
      The authors frame this as a new viewpoint they are proposing, which is why
      it is grouped as an emerging rather than canonical model.
pathophysiology:
- name: Formaldehyde delivery at the portal of entry
  biological_scale: TISSUE
  description: >-
    Formaldehyde is small, highly water-soluble, and reacts essentially on
    contact, so the delivered dose is deposited and consumed in the first tissue
    it meets: the ocular surface and upper respiratory mucosa on inhalation, the
    oropharyngeal and gastric mucosa on ingestion, the epidermis on skin
    contact. More than 90% of inhaled formaldehyde is retained in the upper
    airway. This scrubbing at the portal of entry is the single organizing
    principle of the disease - it is why injury is concentration-driven rather
    than cumulative-dose-driven, and why the toxicology of a systemic route is
    so different from that of a local one.
  cell_types:
  - preferred_term: respiratory tract epithelial cell
    term:
      id: CL:0002368
      label: respiratory tract epithelial cell
  downstream:
  - target: Schiff-base adduction and methylene crosslinking of biomolecules
    description: Deposited formaldehyde reacts immediately with nucleophilic groups in the contacted tissue.
  - target: Trigeminal sensory irritation
    description: Formaldehyde at the mucosal surface stimulates trigeminal nerve endings.
  evidence:
  - reference: PMID:39828805
    reference_title: "Formaldehyde and asthma: a plausibility?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Retention of FA in the upper airways is > 90% in agreement with mice exposure studies that only extreme FA concentrations can surpass trachea, travel to the lower airways, and cause mild bronchoconstriction."
    explanation: >-
      Quantifies upper-airway retention and states the corollary that only
      extreme concentrations reach beyond it, supporting portal-of-entry
      deposition.
  - reference: PMID:42101931
    reference_title: "The formaldehyde dispute - Part A: acute and chronic inhalation toxicity and the evolution of scientific knowledge."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "inhalation was illustrated to follow a concentration-dependent continuum of effects confined to the tissues of initial contact"
    explanation: >-
      States the portal-of-entry confinement principle directly. Tagged OTHER
      because this sentence is the review's synthesis across five decades of
      human, animal, and mechanistic studies rather than a single study type.
- name: Schiff-base adduction and methylene crosslinking of biomolecules
  biological_scale: MOLECULAR
  description: >-
    The single chemical event underlying every arm of the disease. The aldehyde
    carbon is electrophilic and attacks nucleophilic sites - lysine
    epsilon-amino and N-terminal amines, cysteine thiols, and the exocyclic
    amines of DNA bases - forming methylol adducts that condense into stable
    methylene bridges. No metabolic activation is required. The same reaction
    that fixes a histology specimen denatures a gastric mucosa, haptenates a
    self protein, and crosslinks DNA to protein.
  biological_processes:
  - preferred_term: peptide cross-linking
    modifier: INCREASED
    term:
      id: GO:0018149
      label: peptide cross-linking
  downstream:
  - target: Protein coagulation and tissue fixation
    description: Crosslinked structural proteins lose their native conformation and function.
  - target: DNA-protein and interstrand crosslink formation
    description: Adduction of DNA bases and adjacent proteins produces covalent DNA lesions.
  - target: Haptenation and type IV sensitization
    description: Covalent modification of self proteins creates neoantigenic hapten-carrier complexes.
  evidence:
  - reference: PMID:40480196
    reference_title: "Emerging mechanisms underlying formaldehyde toxicity and response."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "It rapidly reacts with electron-rich groups in biomolecules like nucleic acids and proteins, leading to cellular damage."
    explanation: >-
      States the shared electrophilic chemistry that produces both the protein
      and the nucleic acid arms of the injury.
  - reference: PMID:30701286
    reference_title: "Evaluation of inhaled low-dose formaldehyde-induced DNA adducts and DNA-protein cross-links by liquid chromatography-tandem mass spectrometry."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The aldehyde moiety tends to react with nucleophilic sites in proteins and DNA, resulting in a number of DNA and protein adducts"
    explanation: >-
      Specifies the aldehyde-nucleophile chemistry and the adduct products that
      follow from it.
- name: Trigeminal sensory irritation
  biological_scale: TISSUE
  description: >-
    Formaldehyde at the ocular and upper-airway surface activates trigeminal
    nerve endings, triggering a reflex cascade of eyeblink, lacrimation,
    rhinorrhoea, and cough. This is the lowest-threshold effect of formaldehyde
    and the endpoint on which most occupational exposure limits are set. The
    early stages are fully reversible; sustained or high exposure carries the
    pathway into neurogenic inflammation and then tissue damage, which is where
    it converges with the cytotoxic arm.
  biological_processes:
  - preferred_term: inflammatory response
    modifier: INCREASED
    term:
      id: GO:0006954
      label: inflammatory response
  downstream:
  - target: Nasal and upper airway epithelial cytotoxicity
    description: >-
      Prolonged or high-concentration stimulation progresses from reversible
      reflex irritation to neurogenic inflammation and epithelial damage.
  evidence:
  - reference: PMID:25182421
    reference_title: "Sensory irritation as a basis for setting occupational exposure limits."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "pathway is initiated by the interaction of local irritants with receptors of the nervous system (e.g., trigeminal nerve endings) and a downstream cascade of reflexes and defense mechanisms (e.g., eyeblinks, coughing)"
    explanation: >-
      Describes the sensory-irritation pathway that this node models, with
      formaldehyde as one of the three index substances in the analysis.
  - reference: PMID:25182421
    reference_title: "Sensory irritation as a basis for setting occupational exposure limits."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "While the first stages of this pathway are thought to be completely reversible, high or prolonged exposure can lead to neurogenic inflammation and subsequently tissue damage."
    explanation: >-
      Supports the reversibility of the early node and the downstream edge to
      epithelial injury at higher or sustained exposure.
- name: Protein coagulation and tissue fixation
  biological_scale: TISSUE
  description: >-
    Extensive crosslinking of structural and enzymatic proteins denatures and
    coagulates them in situ. In the gastrointestinal tract after formalin
    ingestion this is visible at autopsy as literal tissue fixation - the mucosa
    and adjacent organs acquire the rigid, preserved morphology of a specimen.
    Coagulated cellular protein cannot carry out its normal function, so the
    tissue is killed rather than merely injured.
  cell_types:
  - preferred_term: epithelial cell of alimentary canal
    term:
      id: CL:0002251
      label: epithelial cell of alimentary canal
  downstream:
  - target: Coagulative mucosal necrosis and ulceration
    description: Fixed, non-functional tissue undergoes coagulative necrosis with mucosal breakdown.
  - target: Acute circulatory collapse and multiorgan failure
    description: >-
      A proposed direct route in which intravascular fixation of blood
      precipitates acute circulatory failure; curated under an emerging
      hypothesis group, not as established mechanism.
    hypothesis_groups:
    - intravascular_blood_fixation
  evidence:
  - reference: PMID:35394178
    reference_title: "A fatal case of accidental oral formaldehyde poisoning and its pathomorphological characteristics."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the mechanism of death from formaldehyde poisoning is that it rapidly causes coagulation of tissue cell protein, which may lose its normal function"
    explanation: >-
      States protein coagulation with loss of function as the established
      mechanism of tissue injury after formaldehyde ingestion.
  - reference: PMID:35394178
    reference_title: "A fatal case of accidental oral formaldehyde poisoning and its pathomorphological characteristics."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Anatomical examination revealed fixed tissue morphology of the stomach and adjacent organs."
    explanation: >-
      Direct autopsy observation of in-situ tissue fixation in the stomach,
      grounding this node in a human finding rather than in analogy.
- name: Coagulative mucosal necrosis and ulceration
  biological_scale: TISSUE
  description: >-
    Killed mucosa sloughs, producing ulceration, haemorrhage, and - with
    full-thickness injury - perforation and peritonitis. The stomach bears the
    worst of it after ingestion. Loss of the mucosal barrier is also the route
    by which formaldehyde and its metabolites enter the circulation in quantity.
  downstream:
  - target: Systemic absorption and glutathione-dependent oxidation to formate
    description: A denuded, hyperaemic mucosal surface permits large-scale systemic absorption.
  - target: Fibrotic stricture formation
    description: Deep injury heals by granulation and fibrosis rather than by regeneration.
  evidence:
  - reference: PMID:10962510
    reference_title: "Toxicity of ingested formalin and its management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Ingestion can lead to immediate deleterious effects on almost all systems of the body including gastrointestinal tract, central nervous system, cardiovascular system and hepato-renal system, causing gastrointestinal hemorrhage, cardiovascular collapse, unconsciousness or convulsions, severe metabolic acidosis and acute respiratory distress syndrome."
    explanation: >-
      Supports gastrointestinal haemorrhage as a consequence of the corrosive
      mucosal injury, alongside the systemic effects it precedes.
- name: Fibrotic stricture formation
  biological_scale: TISSUE
  conforms_to: "fibrotic_response#Architectural Distortion and Organ Dysfunction"
  description: >-
    Corrosive injury that reaches beyond the mucosa does not regenerate; it
    heals by granulation and collagen deposition, and the scar contracts.
    Weeks after the acute episode this presents as oesophageal stricture and
    gastric outlet obstruction, often requiring repeated endoscopic dilation.
    This is the arm of the disease that persists in survivors, and it follows
    the conserved fibrotic-response pattern of injury to architectural
    distortion rather than anything formaldehyde-specific.
  notes: >-
    The stricture arm is asserted here on the general corrosive-ingestion
    literature and on the depth of injury documented in formaldehyde cases; no
    formaldehyde-specific cohort quantifies stricture incidence, so no
    frequency is curated for the corresponding phenotype.
  downstream:
  - target: Acute circulatory collapse and multiorgan failure
    description: >-
      Full-thickness necrosis progressing to perforation contributes to shock
      and multiorgan failure in the acute phase, before any fibrotic healing.
  evidence:
  - reference: PMID:10962510
    reference_title: "Toxicity of ingested formalin and its management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Formalin is irritating, corrosive and toxic and absorbed from all surfaces of the body."
    explanation: >-
      Establishes the corrosive character of the injury that heals by fibrosis;
      it does not itself document stricture, so this is recorded as partial
      support.
- name: Systemic absorption and glutathione-dependent oxidation to formate
  biological_scale: MOLECULAR
  description: >-
    Absorbed formaldehyde conjugates spontaneously with glutathione to
    S-hydroxymethylglutathione, which ADH5 (alcohol dehydrogenase 5, also called
    formaldehyde dehydrogenase or GSNOR) oxidizes to S-formylglutathione;
    hydrolysis then releases formate. ALDH2 provides a mitochondrial backup arm.
    This is a normal, high-capacity clearance route, not a bioactivation step -
    formaldehyde's blood half-life is very short and the pathway even feeds
    one-carbon metabolism. Toxicity is a capacity-overflow phenomenon: the
    problem is the size of the bolus, not the existence of the pathway. Note the
    contrast with methanol poisoning, where formaldehyde is the intermediate
    being made rather than the poison being cleared.
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  biological_processes:
  - preferred_term: formaldehyde catabolic process
    modifier: INCREASED
    term:
      id: GO:0046294
      label: formaldehyde catabolic process
  - preferred_term: glutathione metabolic process
    modifier: INCREASED
    term:
      id: GO:0006749
      label: glutathione metabolic process
  molecular_functions:
  - preferred_term: S-(hydroxymethyl)glutathione dehydrogenase activity
    modifier: INCREASED
    term:
      id: GO:0051903
      label: S-(hydroxymethyl)glutathione dehydrogenase [NAD(P)+] activity
  downstream:
  - target: Formate accumulation and high anion gap metabolic acidosis
    description: Formate produced faster than folate-dependent clearance can dispose of it accumulates.
  evidence:
  - reference: PMID:33355142
    reference_title: "Digenic mutations in ALDH2 and ADH5 impair formaldehyde clearance and cause a multisystem disorder, AMeD syndrome."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "alcohol dehydrogenase 5 (also known as formaldehyde dehydrogenase or S-nitrosoglutathione reductase, ADH5/FDH/GSNOR) is the principal enzyme converting formaldehyde to formic acid in a glutathione-dependent manner"
    explanation: >-
      Identifies ADH5 as the principal glutathione-dependent enzyme converting
      formaldehyde to formate, which is the chemistry of this node.
  - reference: PMID:33512438
    reference_title: "Analysis of disease model iPSCs derived from patients with a novel Fanconi anemia-like IBMFS ADH5/ALDH2 deficiency."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "We found that ADH5 is the primary defense against formaldehyde, and ALDH2 provides a backup."
    explanation: >-
      Establishes the two-tier structure of the clearance pathway, with ADH5
      primary and ALDH2 as the backup arm.
  - reference: PMID:28813411
    reference_title: "Mammals divert endogenous genotoxic formaldehyde into one-carbon metabolism."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Furthermore, we find that formaldehyde detoxification in human cells generates formate, and thereby promotes nucleotide synthesis."
    explanation: >-
      Confirms formate as the product of human formaldehyde detoxification and
      supports the framing of this route as physiological rather than
      bioactivating.
- name: Formate accumulation and high anion gap metabolic acidosis
  biological_scale: ORGANISM
  description: >-
    Formate is eliminated slowly, by a saturable folate-dependent route, so a
    large formaldehyde load produces formate faster than it can be disposed of.
    Accumulated formate is an unmeasured anion and drives a severe
    high-anion-gap metabolic acidosis; it also inhibits mitochondrial cytochrome
    c oxidase, producing histotoxic hypoxia and lactate that widens the gap
    further. This is the same terminal chemistry as methanol poisoning, which
    matters clinically because commercial formalin is stabilized with methanol
    and the two toxidromes arrive together.
  biological_processes:
  - preferred_term: formate metabolic process
    modifier: INCREASED
    term:
      id: GO:0015942
      label: formate metabolic process
  molecular_functions:
  - preferred_term: cytochrome-c oxidase activity
    modifier: DECREASED
    term:
      id: GO:0004129
      label: cytochrome-c oxidase activity
  notes: >-
    The cytochrome c oxidase inhibition step is carried over from the shared
    formate chemistry established in methanol poisoning; no
    formaldehyde-specific publication measuring complex IV inhibition was
    identified during this curation, so no evidence item is attached to that
    claim here.
  downstream:
  - target: Acute circulatory collapse and multiorgan failure
    description: >-
      Uncorrected severe acidosis and impaired oxidative phosphorylation
      precipitate shock and organ failure.
  evidence:
  - reference: PMID:10962510
    reference_title: "Toxicity of ingested formalin and its management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Ingestion can lead to immediate deleterious effects on almost all systems of the body including gastrointestinal tract, central nervous system, cardiovascular system and hepato-renal system, causing gastrointestinal hemorrhage, cardiovascular collapse, unconsciousness or convulsions, severe metabolic acidosis and acute respiratory distress syndrome."
    explanation: >-
      Places severe metabolic acidosis among the immediate systemic consequences
      of formalin ingestion.
- name: Acute circulatory collapse and multiorgan failure
  biological_scale: ORGANISM
  description: >-
    The terminal common pathway of substantial ingestion: distributive and
    hypovolaemic shock from massive mucosal injury, compounded by refractory
    acidosis and histotoxic hypoxia, producing cardiovascular collapse, CNS
    depression, acute kidney injury, hepatic injury, and acute respiratory
    distress syndrome. Death typically follows within hours to days.
  evidence:
  - reference: PMID:23640147
    reference_title: "Homicidal acute formalin poisoning in an infant from a rural sericulture family presenting with multisystem failure."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Despite proper supportive treatment in the absence of antidote, the infant died within 13 hours after deliberate poisoning."
    explanation: >-
      Documents the fulminant multisystem course and the hours-scale time to
      death in a human case of formalin ingestion.
- name: Nasal and upper airway epithelial cytotoxicity
  biological_scale: TISSUE
  description: >-
    Above the irritant threshold, formaldehyde kills the epithelium it contacts.
    In the chronic rodent inhalation bioassay this appears as rhinitis,
    epithelial dysplasia, and squamous metaplasia, strictly confined to the
    nasal cavity and proximal trachea and graded by concentration. There is a
    sharp transition rather than a smooth ramp: at or below about 2 ppm the
    changes are minimal and reversible, while at 6 ppm and above there is
    persistent epithelial necrosis.
  cell_types:
  - preferred_term: nasopharyngeal epithelial cell
    term:
      id: CL:1001573
      label: nasopharyngeal epithelial cell
  biological_processes:
  - preferred_term: apoptotic process
    modifier: INCREASED
    term:
      id: GO:0006915
      label: apoptotic process
  downstream:
  - target: Regenerative epithelial proliferation and dysplasia
    description: Sustained epithelial killing drives compensatory proliferation of the surviving basal population.
  evidence:
  - reference: PMID:6871871
    reference_title: "Carcinogenicity of formaldehyde in rats and mice after long-term inhalation exposure."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Significant formaldehyde-induced lesions were restricted to the nasal cavity and proximal trachea."
    explanation: >-
      The strongest available demonstration that formaldehyde injury is confined
      to the portal of entry, from the canonical two-year inhalation bioassay.
  - reference: PMID:6871871
    reference_title: "Carcinogenicity of formaldehyde in rats and mice after long-term inhalation exposure."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Rhinitis, epithelial dysplasia, and squamous metaplasia occurred in all exposure groups of rats and in the intermediate and high exposure groups of mice."
    explanation: >-
      Documents the specific epithelial lesions modelled by this node and their
      concentration dependence.
  - reference: PMID:42101931
    reference_title: "The formaldehyde dispute - Part A: acute and chronic inhalation toxicity and the evolution of scientific knowledge."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "whereas exposures ≥6 ppm were associated with persistent epithelial necrosis, regenerative proliferation, and nasal squamous cell carcinomas localized to regions of highest vapor flux in the rat nasal cavity"
    explanation: >-
      Gives the concentration threshold at which reversible adaptive change
      becomes sustained cytotoxic injury. The quoted finding is from the rat
      nasal cavity, hence MODEL_ORGANISM.
- name: DNA-protein and interstrand crosslink formation
  biological_scale: MOLECULAR
  description: >-
    Formaldehyde reacting with DNA yields N2-hydroxymethyl-deoxyguanosine
    mono-adducts, DNA-DNA interstrand crosslinks, and - characteristically -
    covalent DNA-protein crosslinks. These lesions block replication fork
    progression and transcription, and they are the reason formaldehyde is
    genotoxic without requiring metabolic activation. This is also the point at
    which exogenous exposure joins a substantial endogenous background:
    formaldehyde is a normal product of histone and nucleic acid demethylation,
    so every cell already carries these adducts.
  biological_processes:
  - preferred_term: DNA damage response
    modifier: INCREASED
    term:
      id: GO:0006974
      label: DNA damage response
  - preferred_term: interstrand cross-link repair
    modifier: INCREASED
    term:
      id: GO:0036297
      label: interstrand cross-link repair
  downstream:
  - target: Saturation of crosslink repair capacity
    description: Lesions accumulate faster than the crosslink repair machinery can resolve them.
  evidence:
  - reference: PMID:33355142
    reference_title: "Digenic mutations in ALDH2 and ADH5 impair formaldehyde clearance and cause a multisystem disorder, AMeD syndrome."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Aldehydes primarily produce DNA interstrand cross-links (ICL) and nonenzymatic DNA-protein cross-links (DPC)."
    explanation: >-
      Names the two lesion classes this node models and their non-enzymatic
      origin.
  - reference: PMID:26412304
    reference_title: "Endogenous Formaldehyde Is a Hematopoietic Stem Cell Genotoxin and Metabolic Carcinogen."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Endogenous formaldehyde is produced by numerous biochemical pathways fundamental to life, and it can crosslink both DNA and proteins."
    explanation: >-
      Establishes both the crosslinking capability and the endogenous background
      against which exogenous exposure is superimposed.
- name: Saturation of crosslink repair capacity
  biological_scale: CELLULAR
  conforms_to: "genome_instability_mutation#Failure of DNA Damage Surveillance and Repair"
  description: >-
    Formaldehyde-induced crosslinks are resolved by the Fanconi anaemia
    interstrand-crosslink pathway, with FANCD2 as a central node, and by
    DNA-protein-crosslink proteolysis. These systems have finite throughput.
    When the aldehyde burden outruns them, damage persists into replication -
    the injury is not a poisoned enzyme but an exceeded repair budget. This is
    the mechanistic hinge on which both the local carcinogenesis arm and the
    contested haematopoietic arm turn.
  biological_processes:
  - preferred_term: DNA repair
    modifier: DECREASED
    term:
      id: GO:0006281
      label: DNA repair
  downstream:
  - target: Regenerative epithelial proliferation and dysplasia
    description: Unrepaired lesions are fixed as mutations in a proliferating epithelial field.
    hypothesis_groups:
    - portal_of_entry_genotoxicity
  - target: Haematopoietic stem cell genotoxic attrition
    description: >-
      Persistent crosslink damage in haematopoietic stem cells depletes the
      pool; demonstrated for endogenous formaldehyde in genetic models, and
      proposed but not established as a route from inhalational exposure.
    hypothesis_groups:
    - systemic_haematopoietic_genotoxicity
  evidence:
  - reference: PMID:26412304
    reference_title: "Endogenous Formaldehyde Is a Hematopoietic Stem Cell Genotoxin and Metabolic Carcinogen."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The repair of this damage is mediated by FANCD2, a DNA crosslink repair protein."
    explanation: >-
      Identifies the crosslink repair pathway that this node models as being
      saturable by formaldehyde damage.
  - reference: PMID:33355142
    reference_title: "Digenic mutations in ALDH2 and ADH5 impair formaldehyde clearance and cause a multisystem disorder, AMeD syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "our results suggest that the combined deficiency of formaldehyde clearance mechanisms leads to the complex clinical features due to overload of formaldehyde-induced DNA damage, thereby saturation of DNA repair processes"
    explanation: >-
      States the capacity-overflow framing explicitly - disease follows when the
      formaldehyde burden saturates DNA repair.
- name: Regenerative epithelial proliferation and dysplasia
  biological_scale: TISSUE
  description: >-
    Sustained cytotoxicity forces the surviving basal epithelium into continuous
    replacement proliferation. A proliferating field is exactly where unrepaired
    crosslink damage becomes fixed mutation, and the combination of chronic cell
    killing, regenerative division, and local genotoxicity is the accepted mode
    of action for formaldehyde's nasal carcinogenicity. Crucially, the
    non-neoplastic changes regress when exposure stops - it is only the
    carcinoma that does not.
  biological_processes:
  - preferred_term: cell population proliferation
    modifier: INCREASED
    term:
      id: GO:0008283
      label: cell population proliferation
  downstream:
  - target: Upper airway squamous cell carcinoma
    description: Mutations fixed in a chronically proliferating dysplastic field progress to carcinoma.
    hypothesis_groups:
    - portal_of_entry_genotoxicity
  evidence:
  - reference: PMID:42101931
    reference_title: "The formaldehyde dispute - Part A: acute and chronic inhalation toxicity and the evolution of scientific knowledge."
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: "Computational dosimetry, DNA-protein crosslink kinetics, and biologically based dose-response (BBDR) modeling indicated that these outcomes arose from localized tissue injury rather than from cumulative systemic dose."
    explanation: >-
      Supports localized cytotoxic injury with regenerative proliferation, not
      cumulative systemic dose, as the mode of action for the tumour outcome.
      The inference is drawn from dosimetry and BBDR modelling, hence
      COMPUTATIONAL.
  - reference: PMID:6871871
    reference_title: "Carcinogenicity of formaldehyde in rats and mice after long-term inhalation exposure."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "There was regression of rhinitis, dysplasia, and metaplasia at 27 months (3 months postexposure) in the 14.3- and 5.6-ppm groups of mice and in the 2.0- and 5.6-ppm groups of rats."
    explanation: >-
      Demonstrates that the proliferative and dysplastic changes at this node
      are reversible on withdrawal of exposure, unlike the carcinoma downstream
      of them.
- name: Upper airway squamous cell carcinoma
  biological_scale: TISSUE
  description: >-
    The best-anchored malignant endpoint. Squamous cell carcinoma arises at the
    site of maximal vapour flux - the anterior nasal cavity in the rat, the
    nasopharynx in exposed humans - and only in the setting of long-term
    exposure at concentrations that produce sustained cytotoxicity. Human
    epidemiology is not unanimous: the large NCI industrial cohort continues to
    show a nasopharyngeal cancer excess, while an equally large British chemical
    worker cohort found none.
  cell_types:
  - preferred_term: nasopharyngeal epithelial cell
    term:
      id: CL:1001573
      label: nasopharyngeal epithelial cell
  evidence:
  - reference: PMID:6871871
    reference_title: "Carcinogenicity of formaldehyde in rats and mice after long-term inhalation exposure."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Squamous cell carcinomas were observed in the nasal cavities of 103 rats (52 females and 51 males) and 2 male mice exposed to 14.3 ppm and in 2 rats (one male and one female) exposed to 5.6 ppm of formaldehyde gas."
    explanation: >-
      The primary animal demonstration of nasal squamous cell carcinoma, with
      the steep concentration dependence and the large species difference.
  - reference: PMID:23788167
    reference_title: "Mortality from solid tumors among workers in formaldehyde industries: an update of the NCI cohort."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Consistent with previous analyses of this cohort, this update continues to suggest a link between formaldehyde exposure and nasopharyngeal cancer."
    explanation: >-
      Human cohort support for the nasopharyngeal carcinoma endpoint, from the
      largest industrial cohort followed through 2004.
  - reference: PMID:24714728
    reference_title: "Upper airway cancer, myeloid leukemia, and other cancers in a cohort of British chemical workers exposed to formaldehyde."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "Our results provide no support for an increased hazard of myeloid leukemia, nasopharyngeal carcinoma, or other upper airway tumors from formaldehyde exposure."
    explanation: >-
      A comparably large human cohort finding no upper-airway cancer excess,
      recorded so the disagreement between the two cohorts is visible rather
      than resolved by selection.
- name: Haematopoietic stem cell genotoxic attrition
  biological_scale: CELLULAR
  description: >-
    Persistent formaldehyde-crosslink damage in haematopoietic stem cells
    impairs their differentiation and self-renewal and depletes the pool,
    ultimately producing marrow failure and leukaemic clonal evolution. This is
    firmly established for endogenous formaldehyde, in mice lacking clearance or
    repair and in humans with inherited clearance failure. Whether inhaled
    formaldehyde reaches the marrow in sufficient quantity to do the same is the
    contested question behind the IARC leukaemia classification, and is
    deliberately curated here under the alternative hypothesis rather than
    asserted.
  cell_types:
  - preferred_term: hematopoietic stem cell
    term:
      id: CL:0000037
      label: hematopoietic stem cell
  biological_processes:
  - preferred_term: apoptotic process
    modifier: INCREASED
    term:
      id: GO:0006915
      label: apoptotic process
  evidence:
  - reference: PMID:26412304
    reference_title: "Endogenous Formaldehyde Is a Hematopoietic Stem Cell Genotoxin and Metabolic Carcinogen."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Adh5(-/-)Fancd2(-/-) mice reveal an essential requirement for these protection mechanisms in hematopoietic stem cells (HSCs), leading to their depletion and precipitating bone marrow failure."
    explanation: >-
      Demonstrates stem cell depletion and marrow failure from formaldehyde
      damage in a genetic mouse model; supports the mechanism, not the
      inhalational route.
  - reference: PMID:33355142
    reference_title: "Digenic mutations in ALDH2 and ADH5 impair formaldehyde clearance and cause a multisystem disorder, AMeD syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cellular studies revealed that a decrease in the formaldehyde tolerance underlies a loss of differentiation and proliferation capacity of hematopoietic stem cells."
    explanation: >-
      Human cellular evidence that reduced formaldehyde tolerance costs
      haematopoietic stem cells their differentiation and proliferation
      capacity.
  - reference: PMID:30701286
    reference_title: "Evaluation of inhaled low-dose formaldehyde-induced DNA adducts and DNA-protein cross-links by liquid chromatography-tandem mass spectrometry."
    supports: REFUTE
    evidence_source: MODEL_ORGANISM
    snippet: "Moreover, formaldehyde exposure at 1, 30 and 300 ppb did not alter the levels of endogenous formaldehyde-induced DNA adducts or DNA-protein crosslinks."
    explanation: >-
      Argues against low-dose inhaled formaldehyde reaching any tissue as
      genotoxic burden, which is the principal objection to reaching this node
      by the inhalational route.
- name: Haptenation and type IV sensitization
  biological_scale: CELLULAR
  description: >-
    Formaldehyde penetrating skin or airway epithelium covalently modifies self
    proteins, creating hapten-carrier complexes that dendritic cells take up and
    present. Hapten-specific T cells are primed, and on re-exposure mount a
    delayed-type hypersensitivity response - allergic contact dermatitis in
    skin. Sensitization is durable: it does not remit with exposure reduction,
    only with avoidance. Formaldehyde-releasing preservatives are a major and
    often unrecognized source, since a product need not list formaldehyde to
    deliver it.
  cell_types:
  - preferred_term: dendritic cell
    term:
      id: CL:0000451
      label: dendritic cell
  - preferred_term: CD8-positive, alpha-beta T cell
    term:
      id: CL:0000625
      label: CD8-positive, alpha-beta T cell
  biological_processes:
  - preferred_term: inflammatory response
    modifier: INCREASED
    term:
      id: GO:0006954
      label: inflammatory response
  notes: >-
    The cellular steps of haptenation, dendritic cell presentation, and
    hapten-specific T cell priming are the general type IV hypersensitivity
    mechanism applied to formaldehyde; the evidence attached here establishes
    the clinical sensitization and its sources rather than measuring those
    cellular steps for formaldehyde specifically.
  evidence:
  - reference: PMID:18976378
    reference_title: "Occupational contact allergy to formaldehyde and formaldehyde releasers."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Formaldehyde allergy is common and usually derives from formaldehyde-releasing biocides in cosmetic and other products."
    explanation: >-
      Supports formaldehyde sensitization as a common clinical entity and names
      formaldehyde releasers as the usual source.
  - reference: PMID:18976378
    reference_title: "Occupational contact allergy to formaldehyde and formaldehyde releasers."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Reactions to formaldehyde-releasing compounds were seen in 79% of the formaldehyde-allergic patients."
    explanation: >-
      Quantifies cross-reactivity to releasers among sensitized patients,
      supporting the shared haptenation mechanism.
- name: Erythrocyte oxidant injury
  biological_scale: CELLULAR
  description: >-
    A route-specific arm seen when formaldehyde reaches erythrocytes directly in
    the circulation rather than at a mucosal surface - classically iatrogenic
    contamination of dialysate, where residual formalin sterilant is delivered
    intravascularly. Formalin acts as a direct oxidant on red cells, producing
    acute intravascular haemolysis. The route matters: this does not follow from
    inhalational exposure.
  biological_processes:
  - preferred_term: response to oxidative stress
    modifier: INCREASED
    term:
      id: GO:0006979
      label: response to oxidative stress
  evidence:
  - reference: PMID:6705281
    reference_title: "Acute intravascular hemolysis due to accidental formalin intoxication during hemodialysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A patient accidentally exposed to formalin during hemodialysis developed acute intravascular hemolysis."
    explanation: >-
      Documents acute intravascular haemolysis after intravascular formalin
      exposure in a human patient.
  - reference: PMID:6705281
    reference_title: "Acute intravascular hemolysis due to accidental formalin intoxication during hemodialysis."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "In vitro study showed that formalin has direct oxidant action on red blood cells."
    explanation: >-
      Provides the mechanism for the haemolysis - direct oxidant action on
      erythrocytes rather than an immune process.
phenotypes:
- category: Ophthalmologic
  name: Conjunctival irritation
  subtype: Acute inhalation
  description: >-
    Ocular stinging, lacrimation, and conjunctival injection are the earliest
    and most reliable effects of formaldehyde vapour, beginning in the 0.3-0.5
    ppm range.
  phenotype_term:
    preferred_term: Ocular irritation and conjunctival injection
    term:
      id: HP:0000509
      label: Conjunctivitis
    temporality: ACUTE
  evidence:
  - reference: PMID:42101931
    reference_title: "The formaldehyde dispute - Part A: acute and chronic inhalation toxicity and the evolution of scientific knowledge."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Controlled human chamber studies reported no measurable pulmonary impairment below 0.3 ppm, the onset of mild ocular and nasal irritation at 0.3 to 0.5 ppm, and reversible sensory irritation observed at concentrations approaching 1 ppm."
    explanation: >-
      Controlled human exposure data placing ocular irritation at the lowest
      effect threshold for formaldehyde.
- category: Respiratory
  name: Nasal irritation and rhinitis
  subtype: Acute inhalation
  description: >-
    Nasal burning, rhinorrhoea, and mucosal inflammation accompany ocular
    irritation at the same low concentrations, and rhinitis is the earliest
    histological lesion in chronically exposed animals.
  phenotype_term:
    preferred_term: Rhinitis
    term:
      id: HP:0012384
      label: Rhinitis
  evidence:
  - reference: PMID:42101931
    reference_title: "The formaldehyde dispute - Part A: acute and chronic inhalation toxicity and the evolution of scientific knowledge."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Controlled human chamber studies reported no measurable pulmonary impairment below 0.3 ppm, the onset of mild ocular and nasal irritation at 0.3 to 0.5 ppm, and reversible sensory irritation observed at concentrations approaching 1 ppm."
    explanation: >-
      Places nasal irritation alongside ocular irritation at the lowest human
      effect concentrations.
  - reference: PMID:6871871
    reference_title: "Carcinogenicity of formaldehyde in rats and mice after long-term inhalation exposure."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Rhinitis, epithelial dysplasia, and squamous metaplasia occurred in all exposure groups of rats and in the intermediate and high exposure groups of mice."
    explanation: >-
      Rodent inhalation data showing rhinitis at every exposure level;
      supporting, not sole, evidence for the human phenotype.
- category: Respiratory
  name: Cough
  subtype: Acute inhalation
  description: >-
    Cough is part of the trigeminal reflex defence cascade triggered by
    formaldehyde at the airway surface.
  phenotype_term:
    preferred_term: Cough
    term:
      id: HP:0012735
      label: Cough
    temporality: ACUTE
  evidence:
  - reference: PMID:25182421
    reference_title: "Sensory irritation as a basis for setting occupational exposure limits."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "pathway is initiated by the interaction of local irritants with receptors of the nervous system (e.g., trigeminal nerve endings) and a downstream cascade of reflexes and defense mechanisms (e.g., eyeblinks, coughing)"
    explanation: >-
      Names coughing as part of the sensory-irritation reflex cascade for local
      irritants, of which formaldehyde is an index substance in this analysis.
- category: Respiratory
  name: Pharyngeal irritation
  subtype: Acute inhalation
  description: >-
    Throat burning and soreness accompany the nasal and ocular irritant response
    to formaldehyde vapour.
  phenotype_term:
    preferred_term: Throat irritation
    term:
      id: HP:0025439
      label: Pharyngitis
    temporality: ACUTE
  evidence:
  - reference: PMID:32686516
    reference_title: "Formaldehyde toxicity reports from in vitro and in vivo studies: a review and updated data."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Evaluations carried out in experimental studies showed toxic effects on different organs as lung, upper respiratory tract, bone marrow and brain as well as in cells."
    explanation: >-
      Supports upper respiratory tract as a target of formaldehyde toxicity; it
      does not name pharyngitis specifically, hence partial support.
- category: Respiratory
  name: Dyspnea
  subtype: Acute inhalation
  description: >-
    Breathlessness follows higher-concentration exposure, when irritation gives
    way to airway inflammation and, at extreme concentrations, lower-airway
    involvement.
  phenotype_term:
    preferred_term: Dyspnea
    term:
      id: HP:0002094
      label: Dyspnea
  evidence:
  - reference: PMID:39828805
    reference_title: "Formaldehyde and asthma: a plausibility?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Retention of FA in the upper airways is > 90% in agreement with mice exposure studies that only extreme FA concentrations can surpass trachea, travel to the lower airways, and cause mild bronchoconstriction."
    explanation: >-
      Supports lower-airway involvement only at extreme concentrations, which is
      the condition under which dyspnoea is expected; partial because the source
      argues against routine lower-airway effects.
- category: Respiratory
  name: Wheezing
  subtype: Acute inhalation
  description: >-
    Bronchoconstriction with wheeze is reported after high-concentration
    formaldehyde exposure. Note that controlled human exposure studies have not
    reproduced lung-function impairment at typical indoor or occupational
    concentrations, so this phenotype belongs to the extreme end of the exposure
    range rather than to everyday exposure.
  phenotype_term:
    preferred_term: Wheezing
    term:
      id: HP:0030828
      label: Wheezing
  evidence:
  - reference: PMID:39828805
    reference_title: "Formaldehyde and asthma: a plausibility?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Retention of FA in the upper airways is > 90% in agreement with mice exposure studies that only extreme FA concentrations can surpass trachea, travel to the lower airways, and cause mild bronchoconstriction."
    explanation: >-
      Documents bronchoconstriction as an extreme-concentration effect; recorded
      as partial because the same review finds no lung-function impairment up to
      4 ppm in controlled human studies.
- category: Respiratory
  name: Acute respiratory distress syndrome
  subtype: Acute ingestion
  description: >-
    Acute respiratory distress syndrome is described as part of the multisystem
    response to formalin ingestion; very high concentration inhalational
    exposure can separately produce laryngeal and pulmonary oedema.
  phenotype_term:
    preferred_term: Pulmonary edema in acute respiratory distress syndrome
    term:
      id: HP:0100598
      label: Pulmonary edema
    temporality: ACUTE
  evidence:
  - reference: PMID:10962510
    reference_title: "Toxicity of ingested formalin and its management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Ingestion can lead to immediate deleterious effects on almost all systems of the body including gastrointestinal tract, central nervous system, cardiovascular system and hepato-renal system, causing gastrointestinal hemorrhage, cardiovascular collapse, unconsciousness or convulsions, severe metabolic acidosis and acute respiratory distress syndrome."
    explanation: >-
      Names acute respiratory distress syndrome directly among the immediate
      effects of formalin ingestion.
- category: Gastrointestinal
  name: Corrosive gastric injury
  subtype: Acute ingestion
  description: >-
    Swallowed formalin fixes and coagulates the gastric mucosa, producing severe
    epigastric pain, vomiting, and mucosal necrosis. The stomach is the worst
    affected organ.
  phenotype_term:
    preferred_term: Epigastric pain from corrosive gastric injury
    term:
      id: HP:0002027
      label: Abdominal pain
    temporality: ACUTE
  evidence:
  - reference: PMID:35394178
    reference_title: "A fatal case of accidental oral formaldehyde poisoning and its pathomorphological characteristics."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Anatomical examination revealed fixed tissue morphology of the stomach and adjacent organs."
    explanation: >-
      Autopsy documentation of gastric tissue fixation as the corrosive lesion
      of formaldehyde ingestion.
- category: Gastrointestinal
  name: Vomiting
  subtype: Acute ingestion
  description: >-
    Vomiting follows immediately on ingestion of formalin, driven by corrosive
    gastric injury.
  phenotype_term:
    preferred_term: Vomiting
    term:
      id: HP:0002013
      label: Vomiting
    temporality: ACUTE
  evidence:
  - reference: PMID:10962510
    reference_title: "Toxicity of ingested formalin and its management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Ingestion can lead to immediate deleterious effects on almost all systems of the body including gastrointestinal tract, central nervous system, cardiovascular system and hepato-renal system, causing gastrointestinal hemorrhage, cardiovascular collapse, unconsciousness or convulsions, severe metabolic acidosis and acute respiratory distress syndrome."
    explanation: >-
      Supports immediate gastrointestinal injury after ingestion; vomiting
      itself is not named in the quoted text, so this is partial support.
- category: Gastrointestinal
  name: Gastrointestinal hemorrhage
  subtype: Acute ingestion
  description: >-
    Ulceration of the corroded mucosa produces haematemesis and gastrointestinal
    bleeding.
  phenotype_term:
    preferred_term: Gastrointestinal hemorrhage
    term:
      id: HP:0002239
      label: Gastrointestinal hemorrhage
    temporality: ACUTE
  evidence:
  - reference: PMID:10962510
    reference_title: "Toxicity of ingested formalin and its management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Ingestion can lead to immediate deleterious effects on almost all systems of the body including gastrointestinal tract, central nervous system, cardiovascular system and hepato-renal system, causing gastrointestinal hemorrhage, cardiovascular collapse, unconsciousness or convulsions, severe metabolic acidosis and acute respiratory distress syndrome."
    explanation: >-
      Names gastrointestinal haemorrhage explicitly among the immediate effects
      of formalin ingestion.
- category: Gastrointestinal
  name: Esophageal stricture
  subtype: Acute ingestion
  description: >-
    Weeks after a corrosive ingestion, deep injury heals by fibrosis and
    contracts, producing oesophageal stricture and gastric outlet obstruction
    with dysphagia. This is the characteristic late sequela in survivors and
    often requires repeated dilation.
  phenotype_term:
    preferred_term: Esophageal stricture
    term:
      id: HP:0002043
      label: Esophageal stricture
    clinical_course: PROGRESSIVE
  notes: >-
    Curated on the general corrosive-ingestion literature and the depth of
    formaldehyde mucosal injury; no formaldehyde-specific series quantifies
    stricture incidence, so no frequency band is recorded.
  evidence:
  - reference: PMID:10962510
    reference_title: "Toxicity of ingested formalin and its management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Formalin is irritating, corrosive and toxic and absorbed from all surfaces of the body."
    explanation: >-
      Establishes the corrosive injury from which stricture follows; the source
      does not itself document stricture, so support is partial.
- category: Gastrointestinal
  name: Dysphagia
  subtype: Acute ingestion
  description: >-
    Difficulty swallowing occurs acutely from oropharyngeal and oesophageal
    burns and again later from fibrotic stricture.
  phenotype_term:
    preferred_term: Dysphagia
    term:
      id: HP:0002015
      label: Dysphagia
  evidence:
  - reference: PMID:10962510
    reference_title: "Toxicity of ingested formalin and its management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Formalin is irritating, corrosive and toxic and absorbed from all surfaces of the body."
    explanation: >-
      Supports corrosive injury of the swallowing passage; dysphagia is not
      named in the quoted text, so this is partial support.
- category: Metabolic
  name: High anion gap metabolic acidosis
  subtype: Acute ingestion
  description: >-
    Severe metabolic acidosis from accumulated formate, compounded by lactate
    from cytochrome c oxidase inhibition, is the signature laboratory finding
    after substantial formaldehyde ingestion and the main driver of the systemic
    toxidrome.
  phenotype_term:
    preferred_term: High anion gap metabolic acidosis
    term:
      id: HP:0001942
      label: Metabolic acidosis
    severity: SEVERE
    temporality: ACUTE
  evidence:
  - reference: PMID:10962510
    reference_title: "Toxicity of ingested formalin and its management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Ingestion can lead to immediate deleterious effects on almost all systems of the body including gastrointestinal tract, central nervous system, cardiovascular system and hepato-renal system, causing gastrointestinal hemorrhage, cardiovascular collapse, unconsciousness or convulsions, severe metabolic acidosis and acute respiratory distress syndrome."
    explanation: >-
      Names severe metabolic acidosis directly as an immediate consequence of
      formalin ingestion.
- category: Cardiovascular
  name: Circulatory shock
  subtype: Acute ingestion
  description: >-
    Cardiovascular collapse follows from massive mucosal injury, fluid loss, and
    refractory acidosis, and is a leading proximate cause of death.
  phenotype_term:
    preferred_term: Shock
    term:
      id: HP:0031273
      label: Shock
    temporality: ACUTE
  evidence:
  - reference: PMID:10962510
    reference_title: "Toxicity of ingested formalin and its management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Ingestion can lead to immediate deleterious effects on almost all systems of the body including gastrointestinal tract, central nervous system, cardiovascular system and hepato-renal system, causing gastrointestinal hemorrhage, cardiovascular collapse, unconsciousness or convulsions, severe metabolic acidosis and acute respiratory distress syndrome."
    explanation: >-
      Names cardiovascular collapse explicitly among the immediate systemic
      effects of formalin ingestion.
- category: Neurologic
  name: Coma
  subtype: Acute ingestion
  description: >-
    Depressed consciousness progressing to coma reflects the combination of
    severe acidosis, histotoxic hypoxia, and shock.
  phenotype_term:
    preferred_term: Coma
    term:
      id: HP:0001259
      label: Coma
    temporality: ACUTE
  evidence:
  - reference: PMID:10962510
    reference_title: "Toxicity of ingested formalin and its management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Ingestion can lead to immediate deleterious effects on almost all systems of the body including gastrointestinal tract, central nervous system, cardiovascular system and hepato-renal system, causing gastrointestinal hemorrhage, cardiovascular collapse, unconsciousness or convulsions, severe metabolic acidosis and acute respiratory distress syndrome."
    explanation: >-
      Names unconsciousness among the immediate central nervous system effects
      of formalin ingestion.
- category: Neurologic
  name: Seizure
  subtype: Acute ingestion
  description: >-
    Convulsions are described as part of the acute central nervous system
    response to formalin ingestion.
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
    temporality: ACUTE
  evidence:
  - reference: PMID:10962510
    reference_title: "Toxicity of ingested formalin and its management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Ingestion can lead to immediate deleterious effects on almost all systems of the body including gastrointestinal tract, central nervous system, cardiovascular system and hepato-renal system, causing gastrointestinal hemorrhage, cardiovascular collapse, unconsciousness or convulsions, severe metabolic acidosis and acute respiratory distress syndrome."
    explanation: >-
      Names convulsions among the immediate central nervous system effects of
      formalin ingestion.
- category: Renal
  name: Acute kidney injury
  subtype: Acute ingestion
  description: >-
    Renal impairment progressing to anuric failure occurs as part of the
    multiorgan response, from shock, acidosis, and direct toxicity.
  phenotype_term:
    preferred_term: Acute kidney injury
    term:
      id: HP:0001919
      label: Acute kidney injury
    temporality: ACUTE
  evidence:
  - reference: PMID:10962510
    reference_title: "Toxicity of ingested formalin and its management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Ingestion can lead to immediate deleterious effects on almost all systems of the body including gastrointestinal tract, central nervous system, cardiovascular system and hepato-renal system, causing gastrointestinal hemorrhage, cardiovascular collapse, unconsciousness or convulsions, severe metabolic acidosis and acute respiratory distress syndrome."
    explanation: >-
      Names hepato-renal system involvement among the immediate systemic effects
      of formalin ingestion.
- category: Hepatic
  name: Elevated hepatic transaminases
  subtype: Acute ingestion
  description: >-
    Hepatocellular injury with transaminase elevation is part of the
    hepato-renal involvement described after formalin ingestion.
  phenotype_term:
    preferred_term: Elevated hepatic transaminases
    term:
      id: HP:0002910
      label: Elevated circulating hepatic transaminase concentration
    temporality: ACUTE
  evidence:
  - reference: PMID:10962510
    reference_title: "Toxicity of ingested formalin and its management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Ingestion can lead to immediate deleterious effects on almost all systems of the body including gastrointestinal tract, central nervous system, cardiovascular system and hepato-renal system, causing gastrointestinal hemorrhage, cardiovascular collapse, unconsciousness or convulsions, severe metabolic acidosis and acute respiratory distress syndrome."
    explanation: >-
      Supports hepatic involvement; the quoted text does not report transaminase
      values, so support is partial.
- category: Hematologic
  name: Acute intravascular hemolysis
  description: >-
    Direct intravascular exposure - classically formalin contamination of
    dialysate - produces acute haemolysis by direct oxidant action on red cells.
    This is route-specific and is not a feature of inhalational exposure.
  phenotype_term:
    preferred_term: Acute intravascular hemolysis
    term:
      id: HP:0001878
      label: Hemolytic anemia
    temporality: ACUTE
  evidence:
  - reference: PMID:6705281
    reference_title: "Acute intravascular hemolysis due to accidental formalin intoxication during hemodialysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A patient accidentally exposed to formalin during hemodialysis developed acute intravascular hemolysis."
    explanation: >-
      Direct human documentation of acute intravascular haemolysis from
      intravascular formalin exposure.
- category: Dermatologic
  name: Allergic contact dermatitis
  subtype: Chronic exposure
  description: >-
    Repeated skin contact with formaldehyde or, more often, with
    formaldehyde-releasing preservatives, induces type IV sensitization and an
    eczematous dermatitis on re-exposure. Occupational sensitization is common
    in metalworkers, hairdressers, and users of protective creams and
    detergents.
  phenotype_term:
    preferred_term: Eczematous allergic contact dermatitis
    term:
      id: HP:0000964
      label: Eczematoid dermatitis
    temporality: RECURRENT
  notes: >-
    Deliberately carries no `frequency:` band. The best available number - a
    2.88% pooled prevalence of formaldehyde contact allergy across 158 studies
    and over 1.3 million patients - has a denominator of *dermatitis patients
    undergoing patch testing*, not of formaldehyde-exposed people, so mapping it
    onto a FrequencyEnum band would silently change what the number means. It is
    recorded as evidence with its denominator stated instead. Regional variation
    is large (highest in North America at 6.8%), which is a further reason not to
    collapse it to a single band.
  evidence:
  - reference: PMID:18976378
    reference_title: "Occupational contact allergy to formaldehyde and formaldehyde releasers."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The most common source of occupational sensitization was metalworking fluids followed by creams and related products."
    explanation: >-
      Identifies the occupational sources of formaldehyde contact sensitization
      in a patch-test series.
  - reference: PMID:42035787
    reference_title: "The Prevalence of Contact Allergy to Formaldehyde and Formaldehyde Releasers: A Systematic Review and Meta-Analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The pooled prevalence of formaldehyde contact allergy was 2.88% (95% CI 2.55-3.24) with clinical relevance at 41.57%."
    explanation: >-
      Quantifies formaldehyde contact allergy among dermatitis patients across
      158 studies, establishing the phenotype as common and clinically relevant.
      The denominator is patch-tested dermatitis patients, not formaldehyde-exposed
      people, so it grounds the phenotype without supporting a frequency band.
- category: Respiratory
  name: Asthma
  subtype: Chronic exposure
  description: >-
    Asthma and airway hyperreactivity are reported in association with
    formaldehyde exposure, but the causal link is genuinely disputed: controlled
    human exposure studies show no lung-function impairment up to 4 ppm, no
    formaldehyde-specific IgE sensitization has been identified, and the
    supporting meta-analyses draw on observational studies with heavy
    co-exposure confounding. Recorded here as a reported but contested
    association, not an established phenotype.
  phenotype_term:
    preferred_term: Asthma
    term:
      id: HP:0002099
      label: Asthma
  evidence:
  - reference: PMID:39828805
    reference_title: "Formaldehyde and asthma: a plausibility?"
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "The evidence of a direct causal relationship between FA and asthma is insufficient from an experimental viewpoint that includes retention data in the upper airways and controlled animal and human exposure studies."
    explanation: >-
      A review concluding that the causal formaldehyde-asthma link is not
      supported experimentally; recorded to keep the association honestly
      contested rather than asserted.
- category: Neoplastic
  name: Nasopharyngeal squamous cell carcinoma
  subtype: Chronic exposure
  description: >-
    Long-term occupational formaldehyde exposure is associated with
    nasopharyngeal carcinoma, the endpoint underlying the IARC Group 1
    classification, arising at the portal of entry. The human epidemiology is
    not unanimous - two large industrial cohorts disagree - so the association
    is recorded with both.
  phenotype_term:
    preferred_term: Nasopharyngeal squamous cell carcinoma
    term:
      id: HP:0002860
      label: Squamous cell carcinoma
    clinical_course: PROGRESSIVE
    located_in:
      preferred_term: nasopharynx
      term:
        id: UBERON:0001728
        label: nasopharynx
  evidence:
  - reference: PMID:23788167
    reference_title: "Mortality from solid tumors among workers in formaldehyde industries: an update of the NCI cohort."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "With one additional death, previously observed excesses for nasopharyngeal cancer (n = 10) persisted for peak, average intensity and cumulative exposure"
    explanation: >-
      Reports a persisting nasopharyngeal cancer excess with exposure gradient
      in the largest formaldehyde industrial cohort.
  - reference: PMID:24714728
    reference_title: "Upper airway cancer, myeloid leukemia, and other cancers in a cohort of British chemical workers exposed to formaldehyde."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "Our results provide no support for an increased hazard of myeloid leukemia, nasopharyngeal carcinoma, or other upper airway tumors from formaldehyde exposure."
    explanation: >-
      A second large cohort finding no nasopharyngeal carcinoma excess; retained
      so the disagreement between cohorts is explicit in the entry.
- category: Neoplastic
  name: Myeloid leukemia
  subtype: Chronic exposure
  description: >-
    Myeloid leukaemia is the second IARC Group 1 endpoint for formaldehyde and
    the more contested one. The mechanism is established for endogenous
    formaldehyde in genetic clearance failure, but no animal model reproduces
    leukaemia from inhalation, isotope studies find no exogenous adducts at
    distant sites, and cohort epidemiology conflicts. Recorded as a contested
    association attached to the alternative systemic hypothesis.
  phenotype_term:
    preferred_term: Myeloid leukemia
    term:
      id: HP:0012324
      label: Myeloid leukemia
  evidence:
  - reference: PMID:24714728
    reference_title: "Upper airway cancer, myeloid leukemia, and other cancers in a cohort of British chemical workers exposed to formaldehyde."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "Our results provide no support for an increased hazard of myeloid leukemia, nasopharyngeal carcinoma, or other upper airway tumors from formaldehyde exposure."
    explanation: >-
      Directly reports no excess myeloid leukaemia risk in a large exposed
      cohort, which is why this phenotype is curated as contested.
  - reference: PMID:33147438
    reference_title: "Two Aldehyde Clearance Systems Are Essential to Prevent Lethal Formaldehyde Accumulation in Mice and Humans."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "We find that mice lacking two aldehyde detoxifying enzymes, mitochondrial ALDH2 and cytoplasmic ADH5, have greatly shortened lifespans and develop leukemia."
    explanation: >-
      Shows formaldehyde can cause leukaemia when clearance fails genetically;
      partial because this is endogenous overload in a mouse, not inhalational
      exposure in a human.
biochemical:
- name: Serum formate
  notes: >-
    Formate is the mechanistically correct analyte in formaldehyde poisoning.
    Formaldehyde itself has a very short blood half-life and a substantial
    endogenous background, so a blood formaldehyde level is neither sensitive
    nor interpretable in a living patient; formate is what accumulates and what
    drives the acidosis. It is available at reference laboratories but is
    usually too slow to guide the first hours of management, so the anion gap
    serves as the bedside surrogate. No reference interval is curated here
    because none was sourced from a citable publication.
  presence: INCREASED
  evidence:
  - reference: PMID:28813411
    reference_title: "Mammals divert endogenous genotoxic formaldehyde into one-carbon metabolism."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Furthermore, we find that formaldehyde detoxification in human cells generates formate, and thereby promotes nucleotide synthesis."
    explanation: >-
      Establishes formate as the product of human formaldehyde detoxification,
      which is why it is the analyte that accumulates.
- name: Post-mortem blood and tissue formaldehyde
  notes: >-
    In the forensic setting, formaldehyde can be quantified directly in blood
    and gastric tissue and used to confirm the cause of death, with tissue
    concentrations far exceeding blood concentrations because the compound is
    consumed at the site of contact. This is a post-mortem measurement and is
    not a clinical assay for a living patient.
  presence: INCREASED
  evidence:
  - reference: PMID:35394178
    reference_title: "A fatal case of accidental oral formaldehyde poisoning and its pathomorphological characteristics."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The toxicity test results showed that the concentrations of formaldehyde in the blood and gastric tissue were 36.56 mg/kg and 274.48 mg/kg, respectively"
    explanation: >-
      Reports the measured post-mortem blood and gastric tissue concentrations
      used to establish formaldehyde poisoning as the cause of death.
diagnosis:
- name: Acid-base and osmolal gap workup
  description: >-
    There is no useful clinical formaldehyde assay - blood formaldehyde is
    metabolized within minutes against a substantial endogenous background - so
    diagnosis rests on exposure history plus surrogate laboratory findings.
    Arterial blood gas and serum chemistry to establish a high anion gap is the
    diagnostic centrepiece after ingestion. An osmolal gap and a serum methanol
    level should be obtained alongside it, because commercial formalin is
    stabilized with methanol and a significant methanol co-ingestion changes
    management (it, and only it, is the indication for fomepizole).
  diagnosis_term:
    preferred_term: arterial blood gas and anion gap measurement
    term:
      id: NCIT:C217391
      label: Diagnostic Blood Gas Testing
  evidence:
  - reference: PMID:10962510
    reference_title: "Toxicity of ingested formalin and its management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Ingestion can lead to immediate deleterious effects on almost all systems of the body including gastrointestinal tract, central nervous system, cardiovascular system and hepato-renal system, causing gastrointestinal hemorrhage, cardiovascular collapse, unconsciousness or convulsions, severe metabolic acidosis and acute respiratory distress syndrome."
    explanation: >-
      Establishes severe metabolic acidosis as an immediate and expected finding
      after formalin ingestion, which is what makes the acid-base workup the
      diagnostic centrepiece.
- name: Upper gastrointestinal endoscopy with injury grading
  description: >-
    Endoscopy within roughly 12-48 hours of a corrosive ingestion grades the
    depth of mucosal injury (conventionally by the Zargar scale) - early enough
    to grade, late enough for the injury to have declared itself, and before the
    tissue becomes friable enough that scoping risks perforation. The injury
    grade is the best available predictor of both stricture formation and
    mortality after corrosive ingestion, so it drives disposition and the
    intensity of stricture surveillance.
  diagnosis_term:
    preferred_term: upper gastrointestinal endoscopy
    term:
      id: NCIT:C78144
      label: Esophagogastroduodenoscopy
  notes: >-
    Evidence here is from the general corrosive-ingestion literature rather than
    a formaldehyde-specific series; no formaldehyde-only endoscopic cohort was
    identified during this curation.
  evidence:
  - reference: PMID:31643028
    reference_title: "Immediate and long-term outcome of corrosive ingestion."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "High-grade esophageal mucosal injury was associated with a high risk of stricture formation (p = 0.02)."
    explanation: >-
      Quantifies the prognostic value of the endoscopic injury grade for
      stricture formation, which is why endoscopic grading is the pivotal
      diagnostic step after corrosive ingestion.
  - reference: PMID:31643028
    reference_title: "Immediate and long-term outcome of corrosive ingestion."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "There was no relationship between the presence of symptoms or oral mucosal injury and the grades of gastrointestinal mucosal injury."
    explanation: >-
      Supports the need for endoscopy specifically: symptoms and visible oral
      burns do not predict the depth of gastrointestinal injury, so the grade
      cannot be inferred clinically. Partial because the cohort is corrosive
      ingestion generally, not formaldehyde alone.
- name: Patch testing for formaldehyde and formaldehyde releasers
  description: >-
    Suspected formaldehyde allergic contact dermatitis is confirmed by patch
    testing. Formaldehyde sits in most baseline series, but the releasers must be
    tested separately - a product need not declare formaldehyde to deliver it,
    and a negative formaldehyde patch does not exclude releaser allergy.
  diagnosis_term:
    preferred_term: patch testing
    term:
      id: NCIT:C17137
      label: Skin Test
  evidence:
  - reference: PMID:18976378
    reference_title: "Occupational contact allergy to formaldehyde and formaldehyde releasers."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Between January 2001 and May 2007, we had patch tested 81 patients with formaldehyde allergy and 18 with independent allergy to some formaldehyde releaser."
    explanation: >-
      Documents patch testing as the diagnostic method in practice, and shows
      that releaser allergy occurs independently of formaldehyde allergy - the
      reason both are tested.
  - reference: PMID:42035787
    reference_title: "The Prevalence of Contact Allergy to Formaldehyde and Formaldehyde Releasers: A Systematic Review and Meta-Analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The pooled prevalence of formaldehyde contact allergy was 2.88% (95% CI 2.55-3.24) with clinical relevance at 41.57%."
    explanation: >-
      Gives the diagnostic yield of patch testing in the population it is
      actually applied to - dermatitis patients under investigation - pooled
      across 158 studies and over 1.3 million patients.
genetic:
- name: ADH5
  notes: >-
    ADH5 (alcohol dehydrogenase 5, also known as formaldehyde dehydrogenase or
    S-nitrosoglutathione reductase) is the primary cellular defence against
    formaldehyde, oxidizing S-hydroxymethylglutathione en route to formate. It
    is not a causal gene for formaldehyde poisoning - the cause is the exposure -
    but it sets clearance capacity, and biallelic loss-of-function variants
    cause an inherited disorder of endogenous formaldehyde overload. The enzyme
    is deeply conserved from bacteria to mammals, which is itself evidence that
    endogenous formaldehyde has been a persistent pressure.
  relationship_type: SUSCEPTIBILITY
  gene_term:
    preferred_term: ADH5
    term:
      id: hgnc:253
      label: ADH5
  evidence:
  - reference: PMID:33512438
    reference_title: "Analysis of disease model iPSCs derived from patients with a novel Fanconi anemia-like IBMFS ADH5/ALDH2 deficiency."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "We found that ADH5 is the primary defense against formaldehyde, and ALDH2 provides a backup."
    explanation: >-
      Establishes ADH5 as the primary formaldehyde clearance enzyme, so its loss
      reduces the capacity that determines tolerance to a formaldehyde load.
  - reference: PMID:26412304
    reference_title: "Endogenous Formaldehyde Is a Hematopoietic Stem Cell Genotoxin and Metabolic Carcinogen."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Here we show that endogenous formaldehyde is removed by the enzyme alcohol dehydrogenase 5 (ADH5/GSNOR), and Adh5(-/-) mice therefore accumulate formaldehyde adducts in DNA."
    explanation: >-
      Demonstrates that losing ADH5 converts formaldehyde exposure into DNA
      adduct burden, the mechanistic basis for treating it as a susceptibility
      locus.
- name: ALDH2
  notes: >-
    ALDH2 (mitochondrial aldehyde dehydrogenase 2) is the backup arm of
    formaldehyde clearance. The common East Asian variant rs671 (c.1510G>A,
    p.Glu504Lys, ALDH2*2) is dominant-negative - ALDH2 is a tetramer, so one
    defective subunit compromises the assembled enzyme - and is carried by a
    very large fraction of East Asian populations. Whether ALDH2*2 carriers form
    a sensitive tail of the occupational formaldehyde exposure distribution is a
    plausible but untested prediction, recorded as a knowledge gap rather than
    asserted.
  relationship_type: SUSCEPTIBILITY
  gene_term:
    preferred_term: ALDH2
    term:
      id: hgnc:404
      label: ALDH2
  variants:
  - name: ALDH2 rs671 (NM_000690.4:c.1510G>A, p.Glu504Lys)
    description: >-
      The East Asian alcohol-flushing allele, also written ALDH2*2 and, in the
      mature protein numbering, E487K. It acts as a dominant negative on the
      ALDH2 tetramer, so heterozygotes lose most enzyme activity and carry
      reduced backup capacity for formaldehyde clearance.
    evidence:
    - reference: PMID:33355142
      reference_title: "Digenic mutations in ALDH2 and ADH5 impair formaldehyde clearance and cause a multisystem disorder, AMeD syndrome."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Rs671 in the aldehyde dehydrogenase 2 gene (ALDH2) is the cause of Asian alcohol flushing response after drinking."
      explanation: >-
        Identifies the rs671 allele and its population phenotype, in the paper
        that connects it to impaired formaldehyde clearance.
  evidence:
  - reference: PMID:33355142
    reference_title: "Digenic mutations in ALDH2 and ADH5 impair formaldehyde clearance and cause a multisystem disorder, AMeD syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "ALDH2 detoxifies endogenous aldehydes, which are the major source of DNA damage repaired by the Fanconi anemia pathway."
    explanation: >-
      Establishes ALDH2 as an aldehyde clearance enzyme whose failure shifts the
      burden onto DNA crosslink repair.
  - reference: PMID:33147438
    reference_title: "Two Aldehyde Clearance Systems Are Essential to Prevent Lethal Formaldehyde Accumulation in Mice and Humans."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "We show that formaldehyde is a common substrate of ALDH2 and ADH5 and establish methods to quantify elevated blood formaldehyde and formaldehyde-DNA adducts in tissues."
    explanation: >-
      Confirms formaldehyde as a shared substrate of both clearance enzymes,
      which is what makes ALDH2 a modifier of formaldehyde tolerance.
- name: FANCD2
  notes: >-
    FANCD2 is a central component of the Fanconi anaemia interstrand-crosslink
    repair pathway, the system that resolves formaldehyde-induced DNA
    crosslinks. It modifies tolerance downstream of clearance rather than
    upstream of it: clearance sets how much formaldehyde reaches DNA, repair
    sets what happens once it does. Fanconi anaemia patients are therefore a
    biologically motivated formaldehyde-sensitive population, though this has
    not been demonstrated clinically.
  relationship_type: MODIFIER
  gene_term:
    preferred_term: FANCD2
    term:
      id: hgnc:3585
      label: FANCD2
  evidence:
  - reference: PMID:26412304
    reference_title: "Endogenous Formaldehyde Is a Hematopoietic Stem Cell Genotoxin and Metabolic Carcinogen."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The repair of this damage is mediated by FANCD2, a DNA crosslink repair protein."
    explanation: >-
      Identifies FANCD2 as the repair protein handling formaldehyde-induced DNA
      damage, the basis for treating it as a tolerance modifier.
environmental:
- name: Occupational formaldehyde vapour exposure
  exposure_term:
    preferred_term: exposure to formaldehyde
    term:
      id: ECTO:0000439
      label: exposure to formaldehyde
  description: >-
    Anatomy, pathology and histology laboratories, embalming and funeral
    service, wood-composite manufacture using urea- and phenol-formaldehyde
    resins, textile finishing, healthcare disinfection, and hairdressing with
    keratin smoothing treatments are the principal occupational sources. This is
    the dominant population for chronic risk.
  evidence:
  - reference: PMID:32686516
    reference_title: "Formaldehyde toxicity reports from in vitro and in vivo studies: a review and updated data."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Studies with humans gave evidence regarding significant deleterious effects on health associated to chronic FA occupational exposure."
    explanation: >-
      Supports chronic occupational exposure as a documented source of human
      health effects.
  influences_mechanisms:
  - target: Formaldehyde delivery at the portal of entry
    environmental_effect: TRIGGERS
    causal_link_type: DIRECT
    description: >-
      Inhaled formaldehyde vapour is deposited and consumed in the ocular
      surface and upper respiratory mucosa, which is where more than 90% of it
      is retained.
    evidence:
    - reference: PMID:39828805
      reference_title: "Formaldehyde and asthma: a plausibility?"
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Retention of FA in the upper airways is > 90% in agreement with mice exposure studies that only extreme FA concentrations can surpass trachea, travel to the lower airways, and cause mild bronchoconstriction."
      explanation: >-
        Quantifies the upper-airway retention that makes vapour exposure a
        portal-of-entry dose rather than a systemic one.
- name: Ingestion of formalin solution
  exposure_term:
    preferred_term: exposure to formaldehyde
    term:
      id: ECTO:0000439
      label: exposure to formaldehyde
  description: >-
    Swallowing of formalin, whether accidental from decanting into an
    unlabelled beverage container, self-inflicted, or homicidal. The alarming
    odour and immediate pain make this rare, and it is reported
    disproportionately from settings where formalin is domestically or
    industrially accessible.
  evidence:
  - reference: PMID:10962510
    reference_title: "Toxicity of ingested formalin and its management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Ingestion is rare because of alarming odour and irritant effect but documented in accidental, homicidal or suicidal attempts."
    explanation: >-
      Names the three documented intents behind formalin ingestion and explains
      why it is rare.
  - reference: PMID:35394178
    reference_title: "A fatal case of accidental oral formaldehyde poisoning and its pathomorphological characteristics."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This article reports a case of a 50-year-old woman who died after accidentally drinking 25% formaldehyde solution in a transparent plastic bottle."
    explanation: >-
      A documented accidental ingestion arising from decanting formalin into an
      unlabelled beverage container.
  influences_mechanisms:
  - target: Formaldehyde delivery at the portal of entry
    environmental_effect: TRIGGERS
    causal_link_type: DIRECT
    description: >-
      Swallowed formalin delivers a large formaldehyde dose directly onto the
      oropharyngeal and gastric mucosa, where it reacts on contact.
    evidence:
    - reference: PMID:10962510
      reference_title: "Toxicity of ingested formalin and its management."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Formalin is irritating, corrosive and toxic and absorbed from all surfaces of the body."
      explanation: >-
        Supports oral delivery producing both corrosive contact injury and
        systemic absorption.
- name: Indoor air formaldehyde from building products and combustion
  exposure_term:
    preferred_term: exposure to formaldehyde
    term:
      id: ECTO:0000439
      label: exposure to formaldehyde
  description: >-
    Off-gassing from pressed-wood furniture and building products, tobacco
    smoke, combustion, and formaldehyde-releasing consumer products maintain a
    domestic background exposure, higher in new or renovated interiors with poor
    ventilation and at higher temperature and humidity. Typical indoor
    concentrations sit below the sensory irritation threshold.
  evidence:
  - reference: PMID:39828805
    reference_title: "Formaldehyde and asthma: a plausibility?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Formaldehyde (FA) is a ubiquitous indoor air pollutant emitted from construction, consumer, and combustion-related products, and ozone-initiated reactions with reactive organic volatiles."
    explanation: >-
      Identifies the indoor sources of formaldehyde that constitute domestic
      background exposure.
  influences_mechanisms:
  - target: Trigeminal sensory irritation
    environmental_effect: MODULATES
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Indoor formaldehyde contributes to total inhaled dose and can approach the
      sensory irritation threshold in poorly ventilated settings; the cited
      review argues typical indoor concentrations sit well below it, so this is
      recorded as modulating rather than triggering.
    evidence:
    - reference: PMID:39828805
      reference_title: "Formaldehyde and asthma: a plausibility?"
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Typical indoor FA concentrations in public buildings and homes are far below a threshold for sensory irritation in the upper airways, based on controlled human exposure studies, to induce sensory-irritative sensitization nor inflammatory epithelial damage in the airways."
      explanation: >-
        States that typical indoor concentrations fall below the irritation
        threshold, which is why this exposure is curated as modulating total
        dose rather than as a trigger.
- name: Iatrogenic intravascular formalin exposure during hemodialysis
  exposure_term:
    preferred_term: exposure to formaldehyde
    term:
      id: ECTO:0000439
      label: exposure to formaldehyde
  description: >-
    Formalin is used to sterilize dialysis equipment, and residual sterilant
    reaching the extracorporeal circuit delivers formaldehyde straight into the
    bloodstream. This is the one route that bypasses the portal-of-entry
    scrubbing entirely, which is why it produces a haematological injury that
    inhalation does not.
  evidence:
  - reference: PMID:6705281
    reference_title: "Acute intravascular hemolysis due to accidental formalin intoxication during hemodialysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Formalin intoxication should be recognized as a cause of acute hemolysis during hemodialysis and is not invariably fatal, provided further exposure is stopped in time and the complications prevented."
    explanation: >-
      Identifies accidental formalin exposure during haemodialysis as a
      recognized exposure route, and notes it is survivable if exposure stops.
  influences_mechanisms:
  - target: Erythrocyte oxidant injury
    environmental_effect: TRIGGERS
    causal_link_type: DIRECT
    description: >-
      Formalin delivered into the extracorporeal blood circuit contacts
      erythrocytes directly and acts on them as an oxidant.
    evidence:
    - reference: PMID:6705281
      reference_title: "Acute intravascular hemolysis due to accidental formalin intoxication during hemodialysis."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "In vitro study showed that formalin has direct oxidant action on red blood cells."
      explanation: >-
        Establishes the direct oxidant action on erythrocytes that this exposure
        route triggers.
- name: Dermal contact with formaldehyde and formaldehyde-releasing preservatives
  exposure_term:
    preferred_term: exposure to formaldehyde
    term:
      id: ECTO:0000439
      label: exposure to formaldehyde
  description: >-
    Metalworking fluids, protective creams, detergents, liquid soaps, and
    cosmetics preserved with formaldehyde releasers such as quaternium-15 and
    DMDM hydantoin deliver repeated low-level skin exposure. A product need not
    declare formaldehyde to deliver it, which is why releaser allergy is often
    missed.
  evidence:
  - reference: PMID:18976378
    reference_title: "Occupational contact allergy to formaldehyde and formaldehyde releasers."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Exposure to formaldehyde-releasing preservatives in liquid soaps and other rinse-off products was common in both occupational and non-occupational cases."
    explanation: >-
      Documents formaldehyde-releasing preservatives in everyday products as a
      common dermal exposure source.
  influences_mechanisms:
  - target: Haptenation and type IV sensitization
    environmental_effect: TRIGGERS
    causal_link_type: DIRECT
    description: >-
      Repeated skin contact allows formaldehyde to penetrate the epidermis and
      covalently modify self proteins, priming a hapten-specific T cell
      response.
    evidence:
    - reference: PMID:18976378
      reference_title: "Occupational contact allergy to formaldehyde and formaldehyde releasers."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The most common source of occupational sensitization was metalworking fluids followed by creams and related products."
      explanation: >-
        Identifies the dermal exposures that produce documented occupational
        sensitization.
treatments:
- name: Supportive multiorgan care
  description: >-
    There is no antidote for formaldehyde. Management is supportive care of each
    affected organ system: airway protection with early intubation for laryngeal
    oedema, aggressive fluid resuscitation and vasopressors for shock, and
    ventilatory support. Emesis must not be induced and chemical neutralization
    must not be attempted - both re-expose the oesophagus, and neutralization is
    exothermic.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  target_mechanisms:
  - target: Acute circulatory collapse and multiorgan failure
    treatment_effect: MODULATES
    description: >-
      Organ support sustains perfusion and gas exchange while the toxic insult
      is cleared; it does not act on the chemistry upstream of this node.
  evidence:
  - reference: PMID:10962510
    reference_title: "Toxicity of ingested formalin and its management."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "No specific antidote is available. Treatment of toxicity is supportive care of the various organ systems."
    explanation: >-
      States directly that no antidote exists and that supportive organ care is
      the treatment.
- name: Hemodialysis
  description: >-
    Extracorporeal removal is the key intervention in severe poisoning. It
    clears formate, corrects the acidosis, and simultaneously removes the
    methanol that stabilizes commercial formalin. The threshold for starting it
    should be low in a patient with severe high-anion-gap acidosis after
    formalin ingestion.
  therapeutic_modality: DEVICE
  treatment_term:
    preferred_term: hemodialysis
    term:
      id: NCIT:C15248
      label: Hemodialysis
  target_mechanisms:
  - target: Formate accumulation and high anion gap metabolic acidosis
    treatment_effect: INHIBITS
    description: Dialysis removes accumulated formate and corrects the acidosis it drives.
  notes: >-
    Curated on mechanistic grounds shared with methanol poisoning, where
    haemodialysis for formate is standard. No formaldehyde-specific trial
    evidence exists and none plausibly could, so no efficacy claim is made here
    and no evidence item is attached.
- name: Sodium bicarbonate
  description: >-
    Intravenous sodium bicarbonate is given to correct the severe metabolic
    acidosis, buying time while formate is cleared. It treats the consequence,
    not the cause.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: sodium bicarbonate
      term:
        id: CHEBI:32139
        label: sodium hydrogencarbonate
  target_mechanisms:
  - target: Formate accumulation and high anion gap metabolic acidosis
    treatment_effect: MODULATES
    description: >-
      Buffering counteracts the acidaemia produced by accumulated formate
      without removing the formate itself.
  notes: >-
    Standard supportive management for the acidosis of toxic-alcohol and
    aldehyde poisoning; no formaldehyde-specific efficacy publication was
    identified, so no evidence item is attached.
- name: Folinic acid
  description: >-
    Folinic acid supplies the reduced folate cofactor for
    10-formyltetrahydrofolate dehydrogenase, the rate-limiting step in
    converting formate to carbon dioxide, and is used to accelerate formate
    clearance by analogy with methanol poisoning. Note a genuine paradox here:
    while folinic acid is standard acute therapy, folate derivatives are
    themselves a source of formaldehyde by oxidative decomposition of the folate
    backbone, and folate supplementation is cytotoxic to cells that cannot
    detoxify formaldehyde. The two situations are not the same, but the tension
    is worth knowing.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: folinic acid
      term:
        id: CHEBI:63606
        label: (6S)-5-formyltetrahydrofolic acid
  target_mechanisms:
  - target: Formate accumulation and high anion gap metabolic acidosis
    treatment_effect: INHIBITS
    description: Folinic acid accelerates folate-dependent oxidation of formate to carbon dioxide.
  evidence:
  - reference: PMID:28813411
    reference_title: "Mammals divert endogenous genotoxic formaldehyde into one-carbon metabolism."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Here we show that supplementation with tetrahydrofolate, the essential cofactor of this cycle, and other oxidation-prone folate derivatives kills human, mouse and chicken cells that cannot detoxify formaldehyde or that lack DNA crosslink repair."
    explanation: >-
      Cited for the caveat rather than the indication: folate supplementation is
      cytotoxic in clearance-deficient cells, which qualifies the enthusiasm for
      folate rescue in this setting.
- name: Fomepizole
  description: >-
    Fomepizole inhibits alcohol dehydrogenase and is indicated ONLY when there
    is significant methanol co-ingestion, which is common because commercial
    formalin is stabilized with 10-15% methanol. It does not treat formaldehyde
    itself: formaldehyde is already downstream of the alcohol dehydrogenase
    step, so blocking that enzyme does nothing to the formaldehyde already
    present. This distinction is easy to get backwards and matters clinically.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: fomepizole
      term:
        id: CHEBI:5141
        label: fomepizole
  notes: >-
    Deliberately carries no target_mechanisms link in this entry: fomepizole
    acts on the methanol arm of a co-ingestion, not on any node of the
    formaldehyde pathograph. Wiring it to a formaldehyde node would assert
    exactly the error the description warns against.
- name: Removal from exposure
  description: >-
    For the inhalational irritant syndrome and for occupational asthma and
    contact dermatitis, removal from exposure is the definitive intervention.
    The sensory irritation reflex arm is fully reversible in its early stages,
    and the non-neoplastic epithelial changes of chronic exposure regress once
    exposure stops - although carcinoma, once established, does not.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Therapeutic Procedure
    term:
      id: NCIT:C49236
      label: Therapeutic Procedure
  target_mechanisms:
  - target: Nasal and upper airway epithelial cytotoxicity
    treatment_effect: INHIBITS
    description: >-
      Ending exposure removes the driver of epithelial killing and permits
      regression of the non-neoplastic lesions.
  evidence:
  - reference: PMID:6871871
    reference_title: "Carcinogenicity of formaldehyde in rats and mice after long-term inhalation exposure."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "There was regression of rhinitis, dysplasia, and metaplasia at 27 months (3 months postexposure) in the 14.3- and 5.6-ppm groups of mice and in the 2.0- and 5.6-ppm groups of rats."
    explanation: >-
      Demonstrates regression of the non-neoplastic epithelial lesions after
      exposure ends, which is the mechanistic basis for removal from exposure.
- name: Bronchodilator therapy
  description: >-
    Inhaled beta-2 agonists are used for bronchospasm after high-concentration
    inhalational exposure, alongside humidified oxygen and observation for
    delayed pulmonary oedema.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: albuterol
      term:
        id: CHEBI:2549
        label: albuterol
  notes: >-
    Symptomatic management carried over from general irritant-gas exposure; no
    formaldehyde-specific efficacy publication was identified, so no evidence
    item is attached.
- name: Endoscopic dilation of corrosive stricture
  description: >-
    Fibrotic oesophageal strictures and gastric outlet obstruction developing
    weeks after corrosive ingestion are managed with serial endoscopic balloon
    dilation; full-thickness necrosis or perforation requires emergency
    gastrectomy or oesophagectomy.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: endoscopic esophageal dilation
    term:
      id: NCIT:C70908
      label: Esophageal Dilation
  target_mechanisms:
  - target: Fibrotic stricture formation
    treatment_effect: RESTORES
    description: Mechanical dilation restores luminal calibre lost to fibrotic contraction.
  notes: >-
    Standard management of corrosive-ingestion strictures generally; no
    formaldehyde-specific outcome series was identified, so no evidence item is
    attached.
animal_models:
- name: F344 rat two-year formaldehyde inhalation bioassay
  species: Rat
  genotype: Wild-type Fischer 344
  publication: PMID:6871871
  description: >-
    The canonical carcinogenicity model: 0, 2.0, 5.6, and 14.3 ppm formaldehyde
    gas, 6 h/day, 5 days/week for 24 months, with up to 6 months of follow-up
    after exposure ended. It established both the portal-of-entry confinement of
    injury and the steep concentration dependence of the tumour response.
  modeled_mechanisms:
  - target: Nasal and upper airway epithelial cytotoxicity
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      Reproduces concentration-graded rhinitis, epithelial dysplasia, and
      squamous metaplasia strictly confined to the nasal cavity and proximal
      trachea.
    limitations: >-
      Rats are obligate nose-breathers with high nasal deposition, whereas
      humans are oronasal breathers; the rat lesion is anterior nasal while
      human tumours cluster at the nasopharynx, so the anatomical site does not
      transfer directly.
    readouts:
    - name: Nasal epithelial dysplasia and squamous metaplasia
      target: Nasal and upper airway epithelial cytotoxicity
      direction: INCREASED
      interpretation: Histological correlate of the epithelial cytotoxicity node in this model.
      evidence:
      - reference: PMID:6871871
        reference_title: "Carcinogenicity of formaldehyde in rats and mice after long-term inhalation exposure."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "Rhinitis, epithelial dysplasia, and squamous metaplasia occurred in all exposure groups of rats and in the intermediate and high exposure groups of mice."
        explanation: Reports the histological measurement behind this readout.
    - name: Regression of non-neoplastic lesions after exposure ends
      target: Nasal and upper airway epithelial cytotoxicity
      direction: RESTORED
      interpretation: Establishes that this node is reversible, unlike the carcinoma downstream of it.
      evidence:
      - reference: PMID:6871871
        reference_title: "Carcinogenicity of formaldehyde in rats and mice after long-term inhalation exposure."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "There was regression of rhinitis, dysplasia, and metaplasia at 27 months (3 months postexposure) in the 14.3- and 5.6-ppm groups of mice and in the 2.0- and 5.6-ppm groups of rats."
        explanation: Reports the post-exposure regression measurement behind this readout.
    evidence:
    - reference: PMID:6871871
      reference_title: "Carcinogenicity of formaldehyde in rats and mice after long-term inhalation exposure."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Significant formaldehyde-induced lesions were restricted to the nasal cavity and proximal trachea."
      explanation: Supports treating this bioassay as informative for portal-of-entry epithelial injury.
  - target: Upper airway squamous cell carcinoma
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    description: >-
      Produces nasal squamous cell carcinoma, but only at concentrations that
      overwhelm local repair, and at an anatomical site that does not correspond
      to the human nasopharyngeal tumour location.
    limitations: >-
      Tumours arose only at 5.6 and 14.3 ppm, far above human occupational
      exposure, and the near-total absence of tumours in mice at the same
      concentrations shows the response is governed by species-specific nasal
      dosimetry rather than by a species-invariant dose-response.
    readouts:
    - name: Nasal squamous cell carcinoma incidence
      target: Upper airway squamous cell carcinoma
      direction: INCREASED
      interpretation: The tumour endpoint of the bioassay, with its species and concentration dependence.
      evidence:
      - reference: PMID:6871871
        reference_title: "Carcinogenicity of formaldehyde in rats and mice after long-term inhalation exposure."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "Squamous cell carcinomas were observed in the nasal cavities of 103 rats (52 females and 51 males) and 2 male mice exposed to 14.3 ppm and in 2 rats (one male and one female) exposed to 5.6 ppm of formaldehyde gas."
        explanation: Reports the tumour counts by species and concentration behind this readout.
    evidence:
    - reference: PMID:6871871
      reference_title: "Carcinogenicity of formaldehyde in rats and mice after long-term inhalation exposure."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Squamous cell carcinomas were observed in the nasal cavities of 103 rats (52 females and 51 males) and 2 male mice exposed to 14.3 ppm and in 2 rats (one male and one female) exposed to 5.6 ppm of formaldehyde gas."
      explanation: >-
        Supports the model as informative for formaldehyde carcinogenesis while
        showing the species disparity that limits direct human extrapolation.
- name: Adh5-null Fancd2-null mouse
  species: Mouse
  genotype: Adh5-/- Fancd2-/-
  publication: PMID:26412304
  description: >-
    Combined loss of formaldehyde clearance and crosslink repair, which turns
    endogenous formaldehyde into a lethal genotoxin. The reference model for the
    genotoxic arm of formaldehyde biology.
  modeled_mechanisms:
  - target: Haematopoietic stem cell genotoxic attrition
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      Demonstrates that unrepaired formaldehyde crosslink damage depletes
      haematopoietic stem cells and precipitates bone marrow failure, with
      karyomegaly and dysfunction in liver and kidney as well.
    limitations: >-
      This is endogenous formaldehyde overload created by genetic ablation of
      clearance and repair, not inhalational exposure. It establishes that
      formaldehyde can do this to stem cells; it does not establish that inhaled
      formaldehyde reaches them.
    readouts:
    - name: Haematopoietic stem cell depletion and marrow failure
      target: Haematopoietic stem cell genotoxic attrition
      direction: DECREASED
      interpretation: Functional correlate of stem cell attrition in this model.
      evidence:
      - reference: PMID:26412304
        reference_title: "Endogenous Formaldehyde Is a Hematopoietic Stem Cell Genotoxin and Metabolic Carcinogen."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "Adh5(-/-)Fancd2(-/-) mice reveal an essential requirement for these protection mechanisms in hematopoietic stem cells (HSCs), leading to their depletion and precipitating bone marrow failure."
        explanation: Reports the stem cell depletion measurement behind this readout.
    evidence:
    - reference: PMID:26412304
      reference_title: "Endogenous Formaldehyde Is a Hematopoietic Stem Cell Genotoxin and Metabolic Carcinogen."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Formaldehyde is therefore an important source of endogenous DNA damage that is counteracted in mammals by a conserved protection mechanism."
      explanation: >-
        Supports treating this model as informative for the formaldehyde
        genotoxicity node.
  - target: DNA-protein and interstrand crosslink formation
    relationship: MEASURES
    fidelity: HIGH
    description: >-
      Direct mass-spectrometric quantification of formaldehyde-DNA adducts in
      tissue, showing that loss of ADH5 converts formaldehyde burden into DNA
      adduct burden.
    readouts:
    - name: Formaldehyde-DNA adduct accumulation in tissue
      target: DNA-protein and interstrand crosslink formation
      direction: INCREASED
      interpretation: Molecular correlate of the adduct and crosslink node in this model.
      evidence:
      - reference: PMID:26412304
        reference_title: "Endogenous Formaldehyde Is a Hematopoietic Stem Cell Genotoxin and Metabolic Carcinogen."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "Here we show that endogenous formaldehyde is removed by the enzyme alcohol dehydrogenase 5 (ADH5/GSNOR), and Adh5(-/-) mice therefore accumulate formaldehyde adducts in DNA."
        explanation: Reports the adduct measurement behind this readout.
- name: Adh5-null Aldh2 E506K knock-in mouse
  species: Mouse
  genotype: Adh5-/- Aldh2 E506K/E506K
  publication: PMID:33355142
  description: >-
    A genocopy of the two-tier human clearance failure, with the mouse
    equivalent of the human ALDH2 p.Glu504Lys allele on an Adh5-null background.
  modeled_mechanisms:
  - target: Systemic absorption and glutathione-dependent oxidation to formate
    relationship: PERTURBS
    fidelity: HIGH
    description: >-
      Ablates both tiers of the formaldehyde clearance pathway modelled by this
      node, showing what happens when its capacity is removed entirely.
    limitations: >-
      Models loss of clearance capacity rather than an exogenous formaldehyde
      load, and produces a developmental and haematopoietic syndrome that is not
      the phenotype of acute formaldehyde poisoning.
    evidence:
    - reference: PMID:33355142
      reference_title: "Digenic mutations in ALDH2 and ADH5 impair formaldehyde clearance and cause a multisystem disorder, AMeD syndrome."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Moreover, Adh5-/-Aldh2 E506K/E506K double-deficient mice recapitulated key clinical features of AMeDS, showing short life span, dwarfism, and hematopoietic failure."
      explanation: >-
        Supports the model as a faithful genetic ablation of the clearance
        pathway this node describes.
- name: Rat low-dose isotope-labelled formaldehyde inhalation
  species: Rat
  genotype: Wild-type
  publication: PMID:30701286
  description: >-
    Nose-only inhalation of isotope-labelled formaldehyde at 1, 30, and 300 ppb
    for 28 days, with mass-spectrometric discrimination of exogenous from
    endogenous DNA adducts and DNA-protein crosslinks. Designed to answer
    whether inhaled formaldehyde contributes measurable genotoxic burden at
    ambient concentrations.
  modeled_mechanisms:
  - target: DNA-protein and interstrand crosslink formation
    relationship: FAILS_TO_RECAPITULATE
    fidelity: HIGH
    description: >-
      At environmentally relevant concentrations, inhaled formaldehyde produced
      no detectable exogenous adducts in any tissue - including the nasal
      epithelium - and did not change the endogenous adduct burden. The node is
      real, but low-dose inhalation does not reach it.
    limitations: >-
      Tested only up to 300 ppb, far below the concentrations at which the
      rodent bioassay produces tumours, so this is a statement about ambient
      exposure rather than about occupational peaks or the rat carcinogenicity
      range.
    readouts:
    - name: Exogenous formaldehyde-DNA adducts and DNA-protein crosslinks
      target: DNA-protein and interstrand crosslink formation
      direction: UNCHANGED
      interpretation: >-
        A negative result at ambient concentrations, and the load-bearing
        evidence for the portal-of-entry hypothesis.
      evidence:
      - reference: PMID:30701286
        reference_title: "Evaluation of inhaled low-dose formaldehyde-induced DNA adducts and DNA-protein cross-links by liquid chromatography-tandem mass spectrometry."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "Moreover, formaldehyde exposure at 1, 30 and 300 ppb did not alter the levels of endogenous formaldehyde-induced DNA adducts or DNA-protein crosslinks."
        explanation: Reports the negative adduct measurement behind this readout.
    evidence:
    - reference: PMID:30701286
      reference_title: "Evaluation of inhaled low-dose formaldehyde-induced DNA adducts and DNA-protein cross-links by liquid chromatography-tandem mass spectrometry."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Our data clearly show that endogenous adducts are present in all tissues analyzed, but exogenous adducts were not detectable in any tissue samples, including the most susceptible nasal epithelium."
      explanation: >-
        Substantiates the negative claim that low-dose inhalation does not add
        to the genotoxic burden at this node.
experimental_models:
- name: ADH5/ALDH2-deficient patient-derived iPSC haematopoietic differentiation
  experimental_model_type: IPSC_DERIVED_MODEL
  description: >-
    Induced pluripotent stem cells from patients with biallelic ADH5 variants
    plus a heterozygous ALDH2*2 allele, differentiated toward haematopoiesis,
    used to establish the hierarchy of the two clearance enzymes in a human
    genetic background.
  publication: PMID:33512438
  modeled_mechanisms:
  - target: Systemic absorption and glutathione-dependent oxidation to formate
    relationship: PERTURBS
    fidelity: HIGH
    description: >-
      Human cells with graded clearance defects establish that ADH5 is the
      primary formaldehyde defence and ALDH2 the backup, which is the two-tier
      structure this node describes.
    limitations: >-
      An in vitro differentiation system driven by endogenous formaldehyde, not
      a model of exogenous exposure; it speaks to clearance capacity rather than
      to the toxicology of a swallowed or inhaled dose.
    readouts:
    - name: Spontaneous sister chromatid exchange in patient lymphocytes
      target: Systemic absorption and glutathione-dependent oxidation to formate
      direction: INCREASED
      interpretation: >-
        A cellular readout that clearance failure translates into
        recombinational repair of formaldehyde damage; notably cell-type
        dependent, since patient fibroblasts were normal.
      evidence:
      - reference: PMID:33512438
        reference_title: "Analysis of disease model iPSCs derived from patients with a novel Fanconi anemia-like IBMFS ADH5/ALDH2 deficiency."
        supports: SUPPORT
        evidence_source: HUMAN_CLINICAL
        snippet: "Phytohemagglutinin-stimulated lymphocytes from these patients displayed highly increased numbers of spontaneous sister chromatid exchanges (SCEs), reflecting homologous recombination repair of formaldehyde damage."
        explanation: Reports the sister chromatid exchange measurement behind this readout.
    evidence:
    - reference: PMID:33512438
      reference_title: "Analysis of disease model iPSCs derived from patients with a novel Fanconi anemia-like IBMFS ADH5/ALDH2 deficiency."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "We found that ADH5 is the primary defense against formaldehyde, and ALDH2 provides a backup."
      explanation: >-
        Supports the model as informative for the structure of the clearance
        pathway at this node.
differential_diagnoses:
- name: Methanol poisoning
  disease_term:
    preferred_term: methanol poisoning
    term:
      id: MONDO:0017860
      label: methanol poisoning
  distinguishing_features:
  - Shares formate accumulation, high-anion-gap acidosis, and visual loss, but lacks corrosive gastrointestinal injury
  - Distinguished by an elevated osmolal gap and detectable serum methanol
  - Frequently coexists, because commercial formalin is stabilized with 10-15% methanol
  - Fomepizole is indicated for methanol and useless against formaldehyde already formed
  description: >-
    The most important differential and also the most common co-diagnosis. In
    methanol poisoning formaldehyde is the transient intermediate being
    produced; in formaldehyde poisoning it is the poison being cleared. Both
    converge on formate.
- name: Acid or alkali caustic ingestion
  distinguishing_features:
  - Corrosive gastrointestinal injury without the disproportionate systemic acidosis of formalin
  - Alkali produces deeper liquefactive oesophageal injury; formaldehyde produces coagulative fixation
  description: >-
    Other caustic ingestions produce a similar corrosive picture but do not
    carry the systemic formate load, so the depth of acidosis is the
    discriminator.
- name: ADH5/ALDH2 deficiency (AMeD syndrome)
  distinguishing_features:
  - No exogenous exposure; disease arises from failure to clear endogenous formaldehyde
  - Childhood onset with aplastic anaemia, short stature, and intellectual disability
  - Digenic - biallelic ADH5 variants plus the heterozygous ALDH2 rs671 allele
  - Chromosome fragility testing is negative, distinguishing it from Fanconi anaemia
  description: >-
    The inherited mirror image of this entry: the same molecule, no exposure at
    all, because the drain is blocked rather than the tap left running. It is a
    separate disease entity and is not curated here, but it is the mechanistic
    anchor for the genotoxic arm of formaldehyde biology.
  evidence:
  - reference: PMID:38614309
    reference_title: "Characteristic phenotypes of ADH5/ALDH2 deficiency during childhood."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "ADH5/ALDH2 deficiency is a rare inherited syndrome characterized by short stature, microcephaly, delayed mental development, and hematopoietic dysfunction and has recently been proposed as a disease paradigm."
    explanation: >-
      Defines the inherited clearance-failure syndrome and its clinical triad,
      which is what distinguishes it from exposure-driven formaldehyde
      poisoning.
discussions:
- discussion_id: formaldehyde_leukaemia_route
  prompt: >-
    Does inhaled formaldehyde reach haematopoietic stem cells in sufficient
    quantity to cause myeloid leukaemia in humans?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Haematopoietic stem cell genotoxic attrition
  rationale: >-
    IARC classifies formaldehyde as causing myeloid leukaemia, but the route is
    unexplained. Formaldehyde is consumed at the portal of entry;
    isotope-labelled inhalation finds no exogenous adducts at distant sites; no
    animal model reproduces leukaemia from inhalation; and large occupational
    cohorts disagree. The genetic models that do produce leukaemia do so through
    endogenous formaldehyde overload, which is a different exposure. Conflating
    the two is the most common error in this literature, so the systemic route
    is curated as an alternative hypothesis rather than as established
    mechanism.
  proposed_experiments:
  - experiment_id: fa_marrow_adduct_dosimetry
    name: Marrow adduct dosimetry at occupationally relevant formaldehyde concentrations
    description: >-
      Isotope-labelled formaldehyde inhalation at occupationally relevant peak
      concentrations, with adduct quantification in bone marrow rather than only
      at ambient concentrations.
  - experiment_id: fa_aldh2_stratified_cohort
    name: ALDH2 rs671-stratified occupational cohort analysis
    description: >-
      Occupational cohort analysis stratified by ALDH2 rs671 genotype, testing
      whether the clearance-deficient tail of the exposed population carries the
      excess risk if any exists.
  evidence:
  - reference: PMID:24714728
    reference_title: "Upper airway cancer, myeloid leukemia, and other cancers in a cohort of British chemical workers exposed to formaldehyde."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "it remains uncertain how inhaled formaldehyde might reach haematopoietic stem cells at sufficient concentrations to induce malignancy"
    explanation: >-
      States the open dosimetric question that this discussion records.
- discussion_id: rodent_nasal_dosimetry_mismatch
  prompt: >-
    Does the rodent nasal carcinogenicity bioassay translate to human upper
    airway cancer risk, given that the two species breathe differently and
    develop tumours at different sites?
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  attaches_to:
  - pathophysiology#Upper airway squamous cell carcinoma
  rationale: >-
    Rats are obligate nose-breathers with high anterior nasal deposition and
    develop tumours there; humans are oronasal breathers and the epidemiological
    signal is nasopharyngeal. Mice, exposed identically, developed 2 tumours
    where rats developed 103, because they reflexively reduce minute ventilation
    on formaldehyde exposure. The mechanism transfers; the dosimetry may not,
    and the rat tumours arise only at frankly cytotoxic concentrations well
    above human occupational exposure. This is a translational validity
    question, not an absence of evidence.
  proposed_experiments:
  - experiment_id: fa_cfd_nasal_dosimetry
    name: Comparative human-rodent nasal dosimetry with site-specific adduct anchoring
    description: >-
      Computational fluid dynamics dosimetry of human versus rodent nasal and
      nasopharyngeal flux, anchored to measured site-specific adduct burden, to
      test whether the human nasopharyngeal tumour site corresponds to the
      region of highest human vapour flux.
  evidence:
  - reference: PMID:6871871
    reference_title: "Carcinogenicity of formaldehyde in rats and mice after long-term inhalation exposure."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Squamous cell carcinomas were observed in the nasal cavities of 103 rats (52 females and 51 males) and 2 male mice exposed to 14.3 ppm and in 2 rats (one male and one female) exposed to 5.6 ppm of formaldehyde gas."
    explanation: >-
      Quantifies the species disparity at identical exposure that motivates this
      mismatch discussion.
- discussion_id: intravascular_blood_fixation_mechanism
  prompt: >-
    Does formaldehyde cause acute circulatory failure by fixing blood within the
    vasculature, as distinct from shock secondary to mucosal injury and
    acidosis?
  kind: EMERGING_HYPOTHESIS
  status: OPEN
  attaches_to:
  - pathophysiology#Protein coagulation and tissue fixation
  rationale: >-
    A single forensic case report proposes that rapid intravascular fixation of
    blood, rather than the conventional route through mucosal injury and
    acidosis, is the proximate mechanism of death after formaldehyde ingestion.
    It is an interesting reading of the autopsy findings, but it is one case's
    hypothesis, and it is recorded here and grouped under an explicitly emerging
    hypothesis rather than presented as settled mechanism.
  evidence:
  - reference: PMID:35394178
    reference_title: "A fatal case of accidental oral formaldehyde poisoning and its pathomorphological characteristics."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we put forward a new viewpoint on the mechanism of death from formaldehyde poisoning in which formaldehyde causes rapid fixation of blood in the tissue, thus leading to acute circulatory disturbance"
    explanation: >-
      The authors frame this explicitly as a new viewpoint they are proposing,
      which is why it is curated as an emerging hypothesis rather than
      mechanism.
- discussion_id: aldh2_rs671_exposure_interaction
  prompt: >-
    Are ALDH2 rs671 carriers a susceptible subpopulation for occupational
    formaldehyde exposure?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - genetic#ALDH2
  rationale: >-
    ALDH2*2 is dominant-negative and carried by a very large fraction of East
    Asian populations, and it demonstrably reduces formaldehyde tolerance in the
    inherited clearance-failure syndrome. Whether it modifies risk in
    formaldehyde-exposed workers has not, as far as this curation could
    establish, been characterized epidemiologically. This is a large, cheaply
    genotyped population and a testable prediction.
  proposed_experiments:
  - experiment_id: fa_aldh2_genotype_surveillance
    name: Genotype-stratified occupational surveillance in East Asian cohorts
    description: >-
      Genotype-stratified analysis of irritant symptoms, nasal cytology, and
      cancer incidence in East Asian formaldehyde-exposed occupational cohorts.
- discussion_id: folate_paradox_in_formaldehyde_biology
  prompt: >-
    How should folate supplementation be weighed in formaldehyde poisoning,
    given that the folate backbone is itself a formaldehyde source?
  kind: OPEN_QUESTION
  status: OPEN
  attaches_to:
  - treatments#Folinic acid
  rationale: >-
    Folinic acid is used to accelerate formate clearance, by analogy with
    methanol poisoning. Yet oxidation-prone folate derivatives decompose to
    formaldehyde, and folate supplementation kills cells that cannot detoxify it
    or repair its crosslinks. The acute high-formate patient and the chronically
    clearance-deficient cell are not the same situation, but the sign of the
    effect reverses between them, and no study addresses the acute-poisoning
    case directly.
  evidence:
  - reference: PMID:28813411
    reference_title: "Mammals divert endogenous genotoxic formaldehyde into one-carbon metabolism."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Notably, formaldehyde is generated from oxidative decomposition of the folate backbone."
    explanation: >-
      Establishes the folate backbone as a formaldehyde source, which is the
      basis of the paradox this discussion records.
datasets: []

📚

References & Deep Research

Deep Research

1

Claude Code ▸

Formaldehyde Poisoning — Research Report

claude-haiku-4-5-20251001, claude-opus-5[1m] 26 citations 2026-08-13T17:09:31.274250

Formaldehyde Poisoning — Research Report

Prepared: 2026-08-13 · Target entry: kb/disorders/Formaldehyde_Poisoning.yaml · Category: Environmental

0. Framing: this is three diseases wearing one coat

Before the sections, the thing that should shape the whole entry. "Formaldehyde poisoning" is not one pathophysiology — it's a chemical whose damage mode is set almost entirely by dose and route, like how the same enzyme is housekeeping at one concentration and a wrecking ball at another:

Acute corrosive/irritant injury — formaldehyde as a protein crosslinker doing to your stomach lining exactly what it does to a specimen jar. Fast, local, mechanical.
Acute systemic acidosis — the metabolite (formate) is the killer, sharing a final common pathway with methanol poisoning. And formalin usually contains methanol, so you often get both at once.
Chronic genotoxic injury — DNA-protein crosslinks, hematopoietic stem cell attrition, nasal carcinoma. Slow, cumulative, and the one where the genetics live.

There's a fourth: inherited failure to clear endogenous formaldehyde (AMeD syndrome, ADH5/ALDH2). Same molecule, no exposure at all — the body poisons itself because the drain is clogged. That's a separate MONDO entity and probably a separate dismech entry, but it is the mechanistic Rosetta stone for the chronic arm and I've covered it here.

1. Disease Information

Overview

Formaldehyde (HCHO; CHEBI:16842) is a colorless, pungent, highly water-soluble gas — a small, hungry electrophile that grabs nucleophilic amine and thiol groups on proteins and nucleic acids. Formalin is the aqueous form, typically 37–40% formaldehyde by weight, and critically it is usually stabilized with 10–15% methanol to stop polymerization. That methanol is not an incidental impurity; it's a co-poison that changes management.

Formaldehyde poisoning covers acute toxicity from ingestion (formalin — accidental, suicidal, rarely homicidal), inhalation (occupational/industrial, indoor air), dermal/ocular contact, and rare iatrogenic routes (intravesical formalin for refractory hemorrhagic cystitis; dialysate contamination; endodontic formaldehyde-containing sealers).

VERIFIED quote — PMID:10962510 (Pandey CK et al., Hum Exp Toxicol, 2000;19(6):360-6): "Ingestion can lead to immediate deleterious effects on almost all systems of the body including gastrointestinal tract, central nervous system, cardiovascular system and hepato-renal system, causing gastrointestinal hemorrhage, cardiovascular collapse, unconsciousness or convulsions, severe metabolic acidosis and acute respiratory distress syndrome."

VERIFIED quote — PMID:10962510: "No specific antidote is available. Treatment of toxicity is supportive care of the various organ systems."

Identifiers

Resource	ID	Notes
ICD-10-CM	T59.2 (T59.2X1–X4 by intent, +A/D/S encounter)	"Toxic effect of formaldehyde" — this is the gas/vapor branch (T51–T65)
ICD-11	NE61 / NE60-range (toxic effect of corrosive/other substances)	Verify the exact stem code; ICD-11 does not carry a dedicated formaldehyde leaf as cleanly as ICD-10
MeSH	D005557 (Formaldehyde) + `/poisoning` or `/toxicity` subheading	No standalone "formaldehyde poisoning" descriptor
CHEBI	CHEBI:16842 (formaldehyde); CHEBI:17790 (methanol); CHEBI:30751 (formic acid); CHEBI:15740 (formate)	high confidence, still worth an OAK pass
CAS	50-00-0
MONDO	⚠️ NOT RESOLVED. I could not confirm a MONDO term for formaldehyde poisoning in this research.	Do a live OLS/`runoak` lookup before curating. Do not guess — a real-but-wrong MONDO ID is worse than none. Check whether it sits under a chemical-poisoning grouping alongside your existing `Arsenic_Poisoning` entry, and mirror whatever pattern that one used.
OMIM	619151 — AMED SYNDROME, DIGENIC	Not the exposure disease; the inherited clearance failure
Orphanet	No ORPHA code for the acute exposure. AMeD syndrome should have one — check `ORPHA:` cache

Synonyms

Formalin poisoning · formalin intoxication · formaldehyde toxicity · formaldehyde intoxication · methanal poisoning · formol poisoning · (occupational, non-equivalent) formaldehyde-induced occupational asthma; formaldehyde allergic contact dermatitis.

Data provenance character

Predominantly individual case reports and small case series for the acute poisoning (there are no cohorts — nobody runs a formalin-ingestion RCT), occupational cohort epidemiology for the chronic/carcinogenic arm (NCI formaldehyde worker cohort, NIOSH cohort), animal bioassay for the dose-response, and regulatory aggregate documents (ATSDR ToxProfile 111, IARC Monograph 100F, EPA IRIS, NTP RoC). Poison-center aggregate data (AAPCC NPDS) exists but formaldehyde is not broken out cleanly.

2. Etiology

Primary causal factor

Exogenous formaldehyde exposure, dose- and route-dependent. This is a toxicological entry, not a genetic one — the "cause" is the exposure and the modifiers are genetic.

Environmental / exposure risk factors

Occupational (the dominant chronic-risk population): - Anatomy/pathology/histology labs, embalming and funeral service (highest measured exposures — embalmers routinely see peaks >1 ppm) - Wood composites: particleboard, MDF, plywood (urea-formaldehyde and phenol-formaldehyde resins) - Textile finishing (permanent-press resins), paper, foundry (furan binders), plastics/resin manufacture - Healthcare (disinfection, sterilization), agriculture/poultry fumigation, aquaculture (formalin as parasiticide) - Hairdressing — keratin/"Brazilian blowout" smoothing treatments release formaldehyde on heating; FDA has moved toward restricting these

Domestic/environmental: - Off-gassing from pressed-wood furniture and building products (the FEMA trailer episode after Hurricane Katrina is the reference public-health event) - Tobacco smoke (a major indoor contributor), combustion, cooking, candles, incense - New-build/renovated interiors with poor ventilation; higher temperature and humidity accelerate off-gassing - Some cosmetics/personal-care via formaldehyde releasers (quaternium-15, DMDM hydantoin, imidazolidinyl urea, bronopol)

Acute ingestion setting: self-harm (dominant in reported series, especially where formalin is domestically or industrially accessible), accidental decanting into an unlabeled beverage container.

VERIFIED quote — PMID:35394178 (Zhang L et al., Int J Legal Med, 2022): "This article reports a case of a 50-year-old woman who died after accidentally drinking 25% formaldehyde solution in a transparent plastic bottle."

VERIFIED quote — PMID:10962510: "Ingestion is rare because of alarming odour and irritant effect but documented in accidental, homicidal or suicidal attempts."

Host/demographic modifiers: children (smaller dose per kg, higher minute ventilation per kg), asthmatics and atopic individuals (lower irritant threshold), pre-existing airway disease, prior sensitization.

Genetic risk factors — this is the good part

The clearance machinery is a two-tier system, and both tiers have common human variation:

Gene	Role	Variant	Effect
ADH5 (alcohol dehydrogenase 5 / formaldehyde dehydrogenase / GSNOR)	Tier 1 — GSH-dependent oxidation of S-hydroxymethylglutathione, the main cellular formaldehyde drain	Biallelic rare LoF variants	Loss of primary detox
ALDH2 (mitochondrial aldehyde dehydrogenase 2)	Tier 2 — backup aldehyde clearance	rs671, p.Glu504Lys (`ALDH22`; also written E487K in the mature protein) — the East Asian "alcohol flush" allele, dominant-negative*	Reduced backup capacity

ALDH2*2 is carried by an enormous number of people — roughly 28–45% allele-carrier frequency across East Asian populations, on the order of 500+ million people worldwide — which makes it one of the most consequential common variants in human aldehyde biology. Its interaction with formaldehyde exposure is, to my knowledge, not well characterized epidemiologically in FA-exposed workers, and that's a legitimate, flaggable knowledge gap for the entry.

VERIFIED quote — PMID:33355142 (Oka Y et al., Sci Adv, 2020): "Here, we show that the rs671 defective allele in combination with mutations in the alcohol dehydrogenase 5 gene, which encodes formaldehyde dehydrogenase (ADH5FDH), causes a previously unidentified disorder, AMeD (aplastic anemia, mental retardation, and dwarfism) syndrome."

Downstream of clearance, the repair genes matter too: FANCD2 and the broader Fanconi anemia/BRCA interstrand-crosslink pathway, DNA-protein-crosslink proteases (SPRTN), the p97/VCP unfoldase, and POLQ (theta-mediated end joining). Fanconi anemia patients are, in principle, a formaldehyde-hypersensitive population — though I'd treat "FA patients should avoid FA exposure" as biologically motivated rather than clinically demonstrated.

Protective factors

Environmental: ventilation, low-emission (CARB Phase 2 / TSCA Title VI compliant) composite wood, substitution of formaldehyde-free resins, engineering controls, respiratory protection. These are engineering facts, not epidemiologic "protective factor" findings.
Genetic: none established. Wild-type ALDH2/ADH5 is baseline capacity, not protection.
⚠️ Folate is a trap. The intuitive move — "give folate, it feeds one-carbon metabolism" — is complicated by Burgos-Barragan's finding that the folate backbone itself decomposes into formaldehyde:

VERIFIED quote — PMID:28813411 (Burgos-Barragan G et al., Nature, 2017): "Here we show that supplementation with tetrahydrofolate, the essential cofactor of this cycle, and other oxidation-prone folate derivatives kills human, mouse and chicken cells that cannot detoxify formaldehyde or that lack DNA crosslink repair. Notably, formaldehyde is generated from oxidative decomposition of the folate backbone."

This is a genuinely nice curation nugget: folinic acid is standard acute therapy (to push formate → CO₂) while folate supplementation is cytotoxic in clearance-deficient cells. Same molecule class, opposite sign, depending on which arm of the disease you're in. Worth an explicit discussions: block.

Gene–environment interaction

The cleanest GxE story here is endogenous: ADH5^-/- + ALDH2*2 produces disease with no exogenous exposure whatsoever, because the body's own metabolism generates enough formaldehyde to be lethal to stem cells. That establishes the mechanism; exogenous exposure then adds to the same pool. A plausible (and untested) prediction: ALDH2*2 carriers with ADH5 heterozygosity should be the sensitive tail of the occupational exposure distribution. Flag as KNOWLEDGE_GAP.

3. Phenotypes

⚠️ All HPO IDs below need just validate-terms / OAK confirmation before curation. I've marked confidence. Frequencies are largely qualitative — the acute literature is case reports, so omit frequency: rather than manufacture a band (per your frequency-evidence SOP).

A. Acute inhalation (irritant syndrome) — onset minutes, course acute/self-limited if exposure ends

Phenotype	Suggested HP	Conf.	Notes
Eye irritation / lacrimation	HP:0000509 (blepharitis? — verify)	low	Threshold ~0.5–1 ppm; the earliest and most reliable effect
Nasal/throat irritation, rhinitis	HP:0002333 (verify)	low
Cough	HP:0012735	high
Dyspnea	HP:0002094	high
Wheezing / bronchospasm	HP:0030828	high	Sensitized individuals react at ≈0.3 ppm
Respiratory distress	HP:0002098	med
Pulmonary edema (high concentration)	HP:0100598 (verify)	med	~50–100 ppm range
Chemical pneumonitis	HP:0006536 / HP:0002090 (verify)	low
Hypoxemia	HP:0012418 (verify)	med

Dose landmarks worth curating as notes: irritation ~0.5–2 ppm; intolerable irritation 10–20 ppm; NIOSH IDLH 20 ppm; pulmonary edema/laryngospasm 50–100 ppm; potentially fatal >100 ppm.

B. Acute ingestion (corrosive + systemic) — onset minutes to hours, severe, often fatal

Local corrosive: - Oropharyngeal/esophageal/gastric burns; severe epigastric and retrosternal pain (HP:0011established — use HP:0002027 Abdominal pain, verify) - Odynophagia, drooling, vomiting (HP:0002013), hematemesis, GI hemorrhage (HP:0002239, verify) - Gastric perforation, peritonitis - The stomach is preferentially hit — formaldehyde "fixes" the mucosa the way it fixes a specimen

Systemic: - Severe high-anion-gap metabolic acidosis (HP:0001942 Metabolic acidosis, verify) — the signature lab finding, driven by formate + lactate - Circulatory shock / cardiovascular collapse - CNS depression → coma (HP:0001259, verify), seizures (HP:0001250) - Acute kidney injury (HP:0001919, verify) progressing to anuric renal failure - Hepatic injury, transaminase elevation (HP:0002910, verify) - ARDS - Hemolysis (reported with formic acid), DIC - Visual disturbance/blindness — if methanol co-ingestion is significant; formate is the optic-nerve toxin common to both

Late/delayed (weeks): - Esophageal stricture and gastric outlet obstruction — the fibrotic sequela; documented specifically after formaldehyde ingestion. Onset typically 2–8 weeks post-injury.

C. Chronic exposure

Occupational asthma / airway hyperreactivity (HP:0002099 Asthma, verify)
Allergic contact dermatitis (HP:0000964 Eczema, verify) — type IV hypersensitivity to formaldehyde and releasers. Meta-analytic contact-allergy prevalence ≈2.6% adults / 3.0% children, highest in North America (~6.8%) ⚠️ UNVERIFIED (search summary of PMID:42035787 — that PMID looks anomalously high, check it exists before citing)
Chronic rhinitis, nasal epithelial dysplasia/metaplasia
Reduced pulmonary function on longitudinal occupational follow-up
Nasopharyngeal carcinoma; myeloid leukemia (IARC Group 1 endpoints)
Reported but contested: neurocognitive/memory complaints, sick-building-syndrome symptom clusters, adverse reproductive outcomes

D. Inherited clearance failure (AMeD syndrome) — separate entity, childhood onset

Core triad across the reported cohort: bone marrow failure / aplastic anemia, short stature, intellectual disability. Roughly half show pigmentation changes; ~a quarter skeletal anomalies. Also reported: microcephaly, low birth weight, ophthalmologic findings, immune dysfunction, viral warts, progression to MDS/leukemia requiring HSCT. ⚠️ These cohort proportions come from a paraphrased fetch of PMID:38614309 (Matsumoto et al., Eur J Med Genet, 2024; n=18: 13 F / 5 M) — re-fetch the verbatim abstract before quoting.

Quality of life

No formaldehyde-specific QoL instrument literature found. For the corrosive-stricture survivors, expect the caustic-ingestion QoL profile (dysphagia, repeated dilations, nutritional compromise, psychiatric comorbidity given intent). For occupational asthma/ACD, standard ACQ/DLQI-type impacts. State as not-established rather than inventing numbers.

4. Genetic / Molecular Information

For the exposure disease: no causal gene. Genetics enters as susceptibility and as the mechanistic mirror.

Genes

Gene	HGNC	OMIM	Role
ADH5	hgnc:253 (verify)	*103710	GSH-dependent formaldehyde dehydrogenase (= S-nitrosoglutathione reductase, GSNOR). Tier-1 detox.
ALDH2	hgnc:404 (verify)	*100650	Mitochondrial ALDH; tier-2 backup
FANCD2	hgnc:3585 (verify)	*613984	Repairs formaldehyde-induced DNA crosslinks
ADH1B/ADH1C, ALDH1A1	—	—	Minor/contextual aldehyde handling
SPRTN, VCP, POLQ	—	—	DNA-protein-crosslink resolution and tolerance

(Note the lowercase hgnc: prefix — that's your repo's canonical form.)

Key variants

ALDH2 rs671, c.1510G>A, p.Glu504Lys — missense, dominant-negative (the tetramer is poisoned by one bad subunit, so heterozygotes lose most activity). gnomAD: near-absent in European/African populations, very common East Asian. ClinVar: risk factor / established pharmacogenomic variant (nitroglycerin, alcohol).
ADH5 biallelic LoF — reported variants include nonsense, frameshift, and splice-affecting alleles in Japanese AMeD patients. Rare; carrier frequency not well established outside Japan.

VERIFIED quote — PMID:33355142 (Oka 2020): "Collectively, our results suggest that the combined deficiency of formaldehyde clearance mechanisms leads to the complex clinical features due to overload of formaldehyde-induced DNA damage, thereby saturation of DNA repair processes."

⚠️ PARTIAL/UNVERIFIED fragments — PMID:33512438 (Mu A et al., Blood, 2021): patients carry "biallelic variants in ADH5 combined with a heterozygous ALDH22 dominant-negative allele"; disease-model iPSC hematopoietic differentiation showed "drastically defective cell expansion." Re-fetch for verbatim before use. This paper also establishes ADH5 as primary, ALDH2 as backup, and shows partial rescue by the ALDH2 agonist compound C1* — a nice treatments/experimental_models link.

Functional consequence

Both are LOSS_OF_FUNCTION at the variant level → use GeneticContext.functional_impact_category: LOSS_OF_FUNCTION (or DOMINANT_NEGATIVE specifically for ALDH2*2 — that's exactly the finer distinction your schema wants). At the pathway-node level, the state is reduced formaldehyde catabolism → modifier: DECREASED on the GO process node.

Epigenetics

Formaldehyde perturbs one-carbon metabolism, which is the substrate supply line for SAM-dependent methylation — so global/locus-specific DNA methylation changes are mechanistically plausible and have been reported in exposed workers, but I'd call the human epigenomic evidence thin and not yet curatable as a mechanism node.

Chromosomal

No constitutional abnormality. Acquired: elevated sister chromatid exchange in ADH5/ALDH2-deficient patient lymphocytes (and notably not in their fibroblasts — a nice tissue-specificity detail); formaldehyde causes chromosomal aberrations and micronuclei in exposed workers' lymphocytes and buccal cells. Distinguishing feature vs Fanconi anemia: AMeD patients do not show classic DEB/MMC chromosome fragility, which is diagnostically important.

5. Environmental Information

Chemical: CHEBI:16842. ECTO should have an "exposure to formaldehyde" term (and possibly route-specific children) — look it up rather than trusting me on the ID. For dismech, use influences_mechanisms with environmental_effect: TRIGGERS on the exposure→systemic-burden node, exactly the way Arsenic_Poisoning does it.

Exposure limits (curate as notes, they're regulatory not mechanistic):

Standard	Value
OSHA PEL (8-h TWA)	0.75 ppm
OSHA STEL (15-min)	2 ppm
OSHA Action Level	0.5 ppm
NIOSH REL	0.016 ppm TWA / 0.1 ppm ceiling (15-min) — NIOSH treats it as an occupational carcinogen
NIOSH IDLH	20 ppm
ACGIH TLV	0.1 ppm ceiling (verify current)
WHO indoor air guideline	0.1 mg/m³ (~0.08 ppm), 30-min average

Lifestyle: tobacco smoking is a substantial personal formaldehyde source and a confounder in every occupational leukemia analysis. Alcohol matters indirectly — ALDH2*2 carriers get acetaldehyde loading on top of formaldehyde, competing for the same tier-2 enzyme. Dietary formaldehyde exists (naturally in fruits, fish — especially gadoid fish where TMAO breaks down to formaldehyde) but is not a recognized toxicity source at dietary levels.

Infectious agents: N/A.

6. Mechanism / Pathophysiology

This is the section that should drive the pathophysiology: graph. I've written it as four causal chains with suggested biological_scale tags.

Chain A — Corrosive protein crosslinking (local injury)

Formaldehyde contact with mucosa [MOLECULAR]
  → Schiff-base formation with protein lysine ε-amino and N-terminal amines;
    methylol adducts; methylene (-CH2-) bridge crosslinks [MOLECULAR]
  → protein denaturation/coagulation, loss of native function ("tissue fixation") [MOLECULAR]
  → coagulative necrosis of epithelium and submucosa [TISSUE]
  → mucosal ulceration, hemorrhage, perforation [TISSUE]
  → (weeks) granulation, fibrotic remodeling → stricture / gastric outlet obstruction [TISSUE]

VERIFIED quote — PMID:35394178 (Zhang 2022): "Of late, the mechanism of death from formaldehyde poisoning is that it rapidly causes coagulation of tissue cell protein, which may lose its normal function."

VERIFIED quote — PMID:35394178: "Based on the pathological characteristics of the case, we put forward a new viewpoint on the mechanism of death from formaldehyde poisoning in which formaldehyde causes rapid fixation of blood in the tissue, thus leading to acute circulatory disturbance."

That second one is an interesting and non-consensus claim — intravascular fixation of blood causing acute circulatory failure. Curate it as its own node with supports: PARTIAL and an explicit discussions: entry noting it's a single forensic case's proposed mechanism, not established. Don't launder a hypothesis into settled pathophysiology.

The late stricture arm is a clean candidate for conforms_to: fibrotic_response#....

Chain B — Metabolism to formate → acidosis (systemic injury)

Absorbed formaldehyde [MOLECULAR]
  → spontaneous conjugation with glutathione → S-hydroxymethylglutathione [MOLECULAR]
  → ADH5 (GSH-dependent formaldehyde dehydrogenase) oxidation → S-formylglutathione
    [GO:0046294 formaldehyde catabolic process; GO:0051903 S-(hydroxymethyl)glutathione
     dehydrogenase activity — verify both]
  → esterase hydrolysis → FORMATE [MOLECULAR]
  → formate accumulation exceeding folate-dependent clearance [ORGANISM]
  → (i) high-anion-gap metabolic acidosis [ORGANISM]
    (ii) inhibition of mitochondrial cytochrome c oxidase (complex IV) → histotoxic hypoxia
         → lactate accumulation, compounding the acidosis [CELLULAR]
  → shock, CNS depression, optic neuropathy, multiorgan failure [ORGANISM]

Key kinetic facts for the entry: - Formaldehyde's blood half-life is very short (~1–2 minutes) — it barely exists as formaldehyde once absorbed. This is why blood formaldehyde is useless as a clinical assay and formate is the thing to measure. ⚠️ the specific 1.5-min figure I could not verify in a fetched abstract — treat as UNVERIFIED, source it from ATSDR ToxProfile 111 or IARC Mono 100F. - Endogenous blood formaldehyde in unexposed humans: ~2.61 ± 0.14 µg/g (range 2.05–3.09), i.e. roughly 0.1 mM ⚠️ UNVERIFIED (search summary attributing to IARC Mono 100F / NBK326466). Worth chasing because it's the number that makes the whole "inhalation doesn't raise systemic formaldehyde" argument. - Formate rises fast — reported detectable/high within ~30 min of ingestion. ⚠️ UNVERIFIED. - PMID:7265415 (Eells JT et al., JAMA 1981;246(11):1237-8, "Formaldehyde poisoning. Rapid metabolism to formic acid") is the classic citation for this — but I confirmed it has NO ABSTRACT in PubMed. Per your §4/§6 SOP: you cannot quote it. Cite it in notes, or find a review that states the finding quotably.

Chain C — Genotoxicity → stem cell attrition and carcinogenesis

Formaldehyde (endogenous or exogenous) exceeding ADH5/ALDH2 clearance [MOLECULAR]
  → DNA adducts: N2-hydroxymethyl-deoxyguanosine; dG-dG interstrand crosslinks;
    DNA-PROTEIN CROSSLINKS (DPCs) [MOLECULAR]
  → replication fork stalling and collapse [CELLULAR]
  → engagement of FANCD2 / Fanconi-BRCA interstrand crosslink repair (GO:0036297),
    DPC proteolysis (SPRTN/p97), POLQ-mediated end joining [CELLULAR]
  → when repair capacity is saturated: persistent damage, chromosomal aberration,
    apoptosis of hematopoietic stem cells [CELLULAR]
  → HSC pool depletion → bone marrow failure / aplastic anemia [ORGANISM]
  → surviving damaged clones → clonal evolution → MDS / myeloid leukemia [ORGANISM]

Parallel local arm (inhalation):
  Formaldehyde at portal of entry [MOLECULAR]
  → nasal respiratory epithelial cytotoxicity [CELLULAR]
  → compensatory regenerative cell proliferation + sustained inflammation [TISSUE]
  → fixation of DPC-derived mutations in a proliferating field (incl. p53 mutation)
  → epithelial dysplasia → squamous metaplasia → squamous cell carcinoma [TISSUE]

VERIFIED quote — PMID:26412304 (Pontel LB et al., Mol Cell, 2015): "Endogenous formaldehyde is produced by numerous biochemical pathways fundamental to life, and it can crosslink both DNA and proteins."

VERIFIED quote — PMID:26412304: "Adh5(-/-)Fancd2(-/-) mice reveal an essential requirement for these protection mechanisms in hematopoietic stem cells (HSCs), leading to their depletion and precipitating bone marrow failure. More widespread formaldehyde-induced DNA damage also causes karyomegaly and dysfunction of hepatocytes and nephrons."

VERIFIED quote — PMID:26412304: "Formaldehyde is therefore an important source of endogenous DNA damage that is counteracted in mammals by a conserved protection mechanism."

VERIFIED quote — PMID:32686516 (Bernardini L et al., Drug Chem Toxicol, 2022): "Evaluations carried out in experimental studies showed toxic effects on different organs as lung, upper respiratory tract, bone marrow and brain as well as in cells."

Crucial nuance for the carcinogenesis node — the dose-distribution problem. Stable-isotope work (Swenberg and colleagues, ¹³CD₂-formaldehyde) shows exogenous inhaled formaldehyde forms adducts only at the portal of entry, not at distant sites, and that at low exposures >99% of formaldehyde DNA adducts are endogenous. ⚠️ UNVERIFIED (search summary; primary sources include the Chem Res Toxicol nonhuman-primate ¹³CD₂ paper and PMID:30701286). This is the central argument against a systemic mechanism for formaldehyde-induced leukemia, and it makes leukemia the contested endpoint — nasopharyngeal carcinoma is much better mechanistically anchored. Curate this as an explicit competing-hypothesis structure: mechanistic_hypotheses with a CANONICAL local-genotoxicity model and an ALTERNATIVE/contested systemic model, plus a KNOWLEDGE_GAP discussion. Do not present formaldehyde-leukemia as settled.

Chain D — Immune sensitization

Formaldehyde penetrating skin/airway epithelium [MOLECULAR]
  → haptenation: covalent modification of self proteins [MOLECULAR]
  → dendritic cell uptake and presentation of hapten-modified peptide [CELLULAR]
  → hapten-specific T-cell priming (type IV / delayed hypersensitivity) [CELLULAR]
  → on re-exposure: T-cell-mediated dermatitis (ACD) or airway inflammation [TISSUE]
  → allergic contact dermatitis; occupational asthma [ORGANISM]

Chain E — The salvage arm (why this isn't purely destructive)

Formaldehyde detoxification isn't just disposal — the formate produced feeds nucleotide synthesis.

VERIFIED quote — PMID:28813411 (Burgos-Barragan 2017, Nature): "Furthermore, we find that formaldehyde detoxification in human cells generates formate, and thereby promotes nucleotide synthesis. This supply of 1C units is sufficient to sustain the growth of cells that are unable to use serine, which is the predominant source of 1C units."

Curate this as physiologic context (notes or a non-pathological node) — it's why formaldehyde is a normal metabolite whose toxicity is a capacity-overflow phenomenon, which is the entry's whole thesis.

Suggested ontology terms (⚠️ all need OAK verification)

GO (biological process / molecular function): GO:0046294 formaldehyde catabolic process · GO:0051903 S-(hydroxymethyl)glutathione dehydrogenase activity · GO:0004029 aldehyde dehydrogenase (NAD+) activity · GO:0006730 one-carbon metabolic process · GO:0036297 interstrand cross-link repair · GO:0006281 DNA repair · GO:0034599 cellular response to oxidative stress · GO:0006954 inflammatory response · GO:0006915 apoptotic process · GO:0006749 glutathione metabolic process

CL: CL:0000037 hematopoietic stem cell · CL:0002368 respiratory epithelial cell · CL:0000182 hepatocyte · CL:0000584 enterocyte · CL:0000451 dendritic cell · CL:0000625 CD8+ αβ T cell · CL:0000775 neutrophil

GO cellular component: GO:0005739 mitochondrion (formate/complex IV) · GO:0005634 nucleus (DPC/adducts) · GO:0005829 cytosol (ADH5)

7. Anatomical Structures Affected

Portal of entry dominates. This is the single most important anatomical principle for the entry — formaldehyde is so reactive it mostly doesn't get anywhere.

Inhalation route: - Primary: nasal cavity and nasal mucosa (UBERON:0001707 / UBERON:0001826, verify), nasopharynx, larynx, trachea (UBERON:0003126), proximal bronchi - Secondary at high concentration: lung parenchyma / alveoli (UBERON:0002048), conjunctiva and cornea (UBERON:0000970 eye) - Species note: rats concentrate injury in the anterior nasal respiratory and transitional epithelium — because they're obligate nose-breathers with high nasal deposition. Humans are oronasal breathers with different airflow, and human tumors cluster at the nasopharynx. This anatomical mismatch is a real HUMAN_MODEL_MISMATCH candidate.

Ingestion route: - Primary: oropharynx, esophagus (UBERON:0001043), stomach (UBERON:0000945) — stomach worst hit; duodenum - Secondary: liver (UBERON:0002107), kidney (UBERON:0002113, proximal tubule), brain, heart, lung (ARDS)

Chronic/endogenous: - Bone marrow (UBERON:0002371) — HSC niche - Skin (UBERON:0002097) — ACD - Optic nerve (UBERON:0000941, verify) — formate-mediated, shared with methanol

Subcellular: cytosol (ADH5/GSH detox), mitochondrion (ALDH2; formate-inhibited complex IV), nucleus (adducts, DPCs, crosslinks).

Lateralization: N/A — diffuse/bilateral by exposure geometry.

8. Temporal Development

Arm	Onset	Course
Acute inhalation	Seconds–minutes	Self-limited on removal; RADS/persistent hyperreactivity possible after severe exposure
Acute ingestion	Minutes	Fulminant. Acidosis and shock within hours; death typically within hours to days
Corrosive sequelae	2–8 weeks post-injury	Stricture, gastric outlet obstruction; may need repeated dilation for years
Sensitization (ACD/asthma)	Weeks–months of repeat exposure to induce; minutes–days on re-challenge	Chronic-relapsing, exposure-dependent
Carcinogenesis	Years–decades latency	Progressive
AMeD syndrome	Childhood (growth/development early; marrow failure through childhood)	Progressive; HSCT-requiring

Critical intervention window (acute ingestion): the first hours. Airway protection, bicarbonate, and early hemodialysis for formate. Endoscopy for injury grading is conventionally done within 12–48 hours — early enough to grade, late enough that the injury has declared itself, and before the tissue is friable enough that scoping risks perforation.

Remission: the irritant syndrome resolves with removal. Corrosive damage does not remit — it heals by fibrosis. Sensitization does not remit; it's lifelong immunologic memory.

Nice mechanistic detail on reversibility from the rat bioassay — the non-neoplastic lesions regress after exposure stops, but the carcinomas do not. That's a real, curatable statement about which steps in the chain are reversible:

VERIFIED quote — PMID:6871871 (Kerns WD et al., Cancer Res, 1983): "There was regression of rhinitis, dysplasia, and metaplasia at 27 months (3 months postexposure) in the 14.3- and 5.6-ppm groups of mice and in the 2.0- and 5.6-ppm groups of rats."

9. Inheritance and Population

Epidemiology of poisoning

No reliable prevalence or incidence figures exist for formaldehyde poisoning as such. It is not a reportable condition, poison-center data doesn't break it out cleanly, and the acute literature is case reports. Curate this as NOT_YET_DOCUMENTED / UNKNOWN in the prevalence_class rather than inventing a number. What can be said: - Formalin ingestion is rare in high-income settings (the smell and immediate pain are self-limiting), and disproportionately reported from South and Southeast Asia where formalin is domestically accessible. - Occupational exposure population: on the order of 1–2 million US workers with some formaldehyde exposure ⚠️ UNVERIFIED — source from NIOSH/OSHA regulatory documents.

Corrosive-ingestion outcome benchmarks (⚠️ ALL-CORROSIVE, NOT FORMALIN-SPECIFIC)

Pooled mortality 6.2%, stricture formation 24.7% across 44 studies / >6,000 patients; Grade III injury and intentional ingestion strongly predict both; age >60 an independent mortality risk. ⚠️ UNVERIFIED (search summary of a 2025 Surgery systematic review). If you use these, label them explicitly as caustic-ingestion-general, not formaldehyde-specific — formalin's added systemic formate toxicity means the formaldehyde-specific mortality is almost certainly worse.

Lethal dose

As little as 30 mL (1 oz) of 37% formaldehyde solution has been reported to cause death ⚠️ UNVERIFIED-as-quote (ATSDR MMG for formaldehyde — a citable regulatory document, but it's not a PMID; put it in notes with the URL rather than forcing an evidence: block).

Forensic reference concentrations from a fatal case:

VERIFIED quote — PMID:35394178 (Zhang 2022): "The toxicity test results showed that the concentrations of formaldehyde in the blood and gastric tissue were 36.56 mg/kg and 274.48 mg/kg, respectively, which was consistent with death from formaldehyde poisoning."

For AMeD syndrome

Inheritance: digenic — biallelic ADH5 + ALDH2 rs671. Your CLAUDE.md has a whole section for this: use HP:0010984 Digenic inheritance, bind the term, name both genes in the block description, and cite the digenicity claim separately. This is a textbook exemplar alongside PRPH2-Related_Retinopathy, and it belongs in the Digenic_and_Oligogenic_Disorders grouping.
Reported cases: ~18 patients as of 2024 (13 F, 5 M) ⚠️ from paraphrased fetch — verify.
Population: all reported patients to date are Japanese, which follows directly from ALDH2*2 being effectively an East Asian allele. Not a founder effect in the classical sense — it's a common modifier allele meeting a rare one.
Penetrance/expressivity: variable expressivity is explicit in the 2024 report (mild cases with only growth/developmental findings are missed).

10. Diagnostics

The headline: there is no useful clinical formaldehyde assay.

Blood formaldehyde is metabolized within minutes and there's a substantial endogenous baseline, so a level is neither sensitive nor interpretable in the living patient. Diagnosis is history + syndrome + surrogate labs. (Post-mortem quantification in blood/gastric tissue is meaningful — see the forensic case above.)

Laboratory

Arterial blood gas + serum chemistry → anion gap. Severe HAGMA is the diagnostic centerpiece.
Serum formate — the mechanistically correct analyte; available at reference labs, often too slow to guide the first hours.
Serum lactate — elevated; contributes to the gap.
Osmolal gap + serum methanol — because formalin carries methanol. An osmolal gap points at the methanol co-ingestion and changes management (fomepizole).
CBC, coagulation, LFTs, creatinine/BUN, CK, lipase; type and cross.
LOINC terms exist for formate, methanol, anion gap, lactate — worth binding if you populate biochemical.reference_ranges.

Imaging / endoscopy

Upper GI endoscopy within 12–48 h with Zargar grading (0, 1, 2a/2b, 3a/3b) — the single best predictor of stricture and mortality after any corrosive ingestion.
CT abdomen/chest — increasingly preferred for full-thickness necrosis assessment and surgical triage; better specificity than endoscopy for some outcomes.
Upright CXR / CT for perforation, mediastinitis, ARDS.
Contrast swallow at 2–3 weeks for stricture surveillance.

Functional / other

Spirometry ± methacholine challenge, and serial peak-flow with work/off-work comparison, for suspected occupational asthma.
Patch testing (formaldehyde 2% aq. is in most baseline series; also test formaldehyde releasers separately — a negative formaldehyde patch does not exclude releaser allergy).
Nasal endoscopy/cytology in chronically exposed workers.
Histopathology: coagulative necrosis with "fixed" tissue architecture — pathognomonic-feeling in the forensic setting.

Genetic testing (for AMeD, not for poisoning)

ADH5 + ALDH2 sequencing; the ALDH2 rs671 genotype is on most East Asian arrays.
DEB/MMC chromosome breakage testing is NEGATIVE — this is the key discriminator from Fanconi anemia in a child with marrow failure + short stature + ID.
Elevated sister chromatid exchange in lymphocytes (but normal in fibroblasts).
WES/WGS will find it; a Fanconi/IBMFS panel will only find it if ADH5 and ALDH2 are on the panel — many aren't. Worth stating.

Differential diagnosis

Condition	Distinguishing feature
Methanol poisoning	Shares formate/HAGMA/visual loss. Distinguished by absence of corrosive GI injury and by serum methanol/osmolal gap. Frequently co-exists with formalin ingestion.
Ethylene glycol	Oxalate crystalluria, hypocalcemia, renal failure; no corrosive injury
Acid/alkali caustic ingestion	Corrosive injury without the disproportionate systemic acidosis; alkali causes deeper liquefactive esophageal injury
Salicylate, metformin/lactic acidosis, DKA, uremia	HAGMA without corrosive injury
Glutaraldehyde / other aldehyde exposure	Very similar irritant profile; occupational history
AMeD syndrome vs Fanconi anemia	Negative chromosome fragility, no radial ray defects, digenic genotype

Screening

Occupational medical surveillance under the OSHA formaldehyde standard: exposure monitoring, annual respiratory questionnaire, spirometry, physician evaluation for symptomatic workers.
No population screening. No newborn screening for AMeD (and it wouldn't be actionable at birth).

11. Outcome / Prognosis

Acute ingestion: poor. Substantial formalin ingestion is frequently fatal within hours to days from shock + refractory acidosis + multiorgan failure. Survivors of the acute phase face sepsis, prolonged pulmonary complications, and often gastrectomy.

⚠️ UNVERIFIED (search summary of a Springer/Intensive Care Med case series): two patients ingesting formalin with suicidal intent presented with "extensive gastrointestinal corrosive damage, circulatory shock, metabolic acidosis, respiratory insufficiency and impairment of renal function," both required hemodialysis/hemofiltration, one required gastrectomy, and the course was "characterized by sepsis and protracted pulmonary complications." Track down the PMID and re-fetch — this is a good citation if it verifies.

Prognostic factors: volume and concentration ingested; time to presentation; Zargar endoscopic grade (grade 3b is the inflection point); depth of acidosis / formate level; need for vasopressors; age >60; intentional ingestion.

Acute inhalation: generally good with removal from exposure; high-concentration exposure can leave persistent airway hyperreactivity (RADS).

Chronic: occupational asthma and ACD are chronic-relapsing but not life-limiting. Nasopharyngeal carcinoma prognosis follows standard NPC staging. Formaldehyde-attributable leukemia risk remains contested (see §6).

AMeD: progressive marrow failure requiring HSCT in childhood; the mouse model recapitulates a "short life span."

VERIFIED quote — PMID:33355142 (Oka 2020): "Moreover, Adh5-/-Aldh2 E506K/E506K double-deficient mice recapitulated key clinical features of AMeDS, showing short life span, dwarfism, and hematopoietic failure."

Recovery potential by tissue: epithelial irritation → full recovery. Corrosive full-thickness injury → fibrotic, permanent. HSC depletion → not spontaneously recoverable; requires transplant. Interesting mechanistic finding worth its own node: in the mouse model, bone marrow transplant rescued not only hematopoiesis but also nephron function, implying a hematopoietic contribution to the renal phenotype (see the Pontel quote in §6).

12. Treatment

Central fact: no antidote. Everything is supportive plus enhanced elimination. (VERIFIED — see the PMID:10962510 quote in §1.)

Acute ingestion

Intervention	Detail	Suggested NCIT
Airway protection	Early intubation — laryngeal edema and aspiration risk	NCIT:C49236 Therapeutic Procedure (verify)
Do NOT induce emesis; do NOT attempt chemical neutralization	Re-exposes the esophagus; neutralization is exothermic	—
Activated charcoal	Recommended in ATSDR MMG, though binding of formaldehyde is poor and it obscures endoscopy — contested, curate as such	NCIT:C15986 Pharmacotherapy
Careful gastric lavage/NG suction	Only with a protected airway; contested given perforation risk
IV sodium bicarbonate	For acidosis; ATSDR: adult 1 ampule, pediatric 1 mEq/kg	NCIT:C15986 + CHEBI:32139 sodium bicarbonate (verify)
Aggressive IV fluid resuscitation, vasopressors	Distributive/hypovolemic shock	NCIT:C15747 Supportive Care
Hemodialysis	The key intervention — clears formate and methanol and corrects acidosis. Low threshold.	NCIT — look up "Hemodialysis" (verify)
Folinic acid (leucovorin)	~1 mg/kg IV q4h; accelerates formate → CO₂ via 10-formyl-THF dehydrogenase, the rate-limiting elimination step	NCIT:C15986 + CHEBI folinic acid (verify)
Fomepizole or ethanol	ONLY if significant methanol co-ingestion (serum methanol >20 mg/dL or elevated osmolal gap). Does not treat formaldehyde itself — formaldehyde is already past the ADH step. This distinction matters and is easy to get wrong.	NCIT:C15986
PPI, nutritional support (NJ/TPN)	Mucosal protection, gut rest	NCIT:C15433 Nutritional Support
Surgery	Emergency gastrectomy/esophagectomy for full-thickness necrosis or perforation	NCIT:C15329 Surgical Procedure
Endoscopic balloon dilation	For strictures at 3+ weeks; often serial	NCIT — verify

Acute inhalation

Remove from exposure; humidified oxygen; bronchodilators (β₂-agonists) for bronchospasm; monitor for delayed pulmonary edema for 24–48 h; corticosteroids are used but the evidence is weak — curate as contested. Copious irrigation for eye/skin, ophthalmology referral for corneal injury.

Chronic

ACD: exposure avoidance/substitution (patient-specific allergen lists), topical corticosteroids, emollients
Occupational asthma: removal from exposure is the definitive treatment; ICS/LABA otherwise
Nasopharyngeal carcinoma: standard oncologic management (out of scope for this entry)

AMeD syndrome

Allogeneic HSCT — the definitive therapy for marrow failure. NCIT:C15431 (hematopoietic cell transplantation) → therapeutic_modality: CELL_THERAPY per your mechanical backfill table.
Investigational: ALDH2 agonists (compound C1; Alda-1 is the better-known congener). Partial rescue of hematopoietic expansion in patient-derived iPSC models — a pharmacologic chaperone/activator strategy for the dominant-negative enzyme. therapeutic_modality: SMALL_MOLECULE, preclinical only. Good target_mechanisms link back to the formaldehyde-clearance node with ACTIVATES.
Counsel against alcohol in ALDH2*2 carriers generally (competing substrate load).

Pharmacogenomics

ALDH2 rs671 is an established PGx variant (nitroglycerin bioactivation, alcohol) — relevant context but not a formaldehyde-poisoning treatment decision node today.

Clinical trials

No trials of formaldehyde-poisoning treatment exist or plausibly could. There are ALDH2-activator trials in other indications and general caustic-injury trials. Search ClinicalTrials.gov for "ALDH2" if you want a clinical_trials: block; don't force one for the poisoning itself.

13. Prevention

Primary (this is where nearly all the real-world benefit sits): - Substitution — formaldehyde-free resins, glutaraldehyde-free/formalin-free fixatives where feasible - Engineering controls — local exhaust ventilation at gross-dissection and embalming stations; enclosed processes - Product regulation — TSCA Title VI / CARB ATCM Phase 2 composite-wood emission limits; EU restrictions; FDA action on formaldehyde-releasing hair-smoothing products - Indoor air — WHO 0.1 mg/m³ 30-min guideline; ventilation in new construction; low-emission product selection - Storage/labeling — the fatal case above hinged on formalin in "a transparent plastic bottle." Never decant into food/beverage containers. This is a cheap, high-yield public-health message. - Smoking cessation (personal exposure reduction) - PPE, respiratory protection, training under the OSHA formaldehyde standard (29 CFR 1910.1048)

Secondary: occupational medical surveillance (symptom questionnaire, spirometry); patch testing in workers with suspected ACD; no validated cancer screening for formaldehyde-exposed workers.

Tertiary: post-ingestion stricture surveillance and dilation; complete allergen avoidance after sensitization; job modification/removal for occupational asthma; long-term nutrition and psychiatric follow-up after intentional ingestion.

Genetic counseling: relevant only for AMeD — recurrence risk is complicated by digenicity (an ADH5 carrier couple's risk is conditioned on the ALDH2 genotype segregating too). Worth an explicit note; standard AR recurrence arithmetic doesn't apply cleanly.

Immunization / prophylaxis: N/A.

14. Other Species / Natural Disease

Species (NCBITaxon): Rattus norvegicus (10116), Mus musculus (10090), Macaca spp. / Macaca fascicularis (9541), Equus caballus (9796), Canis lupus familiaris (9615), Gallus gallus (9031, DT40 cells), Danio rerio (7955), Homo sapiens (9606).

Species sensitivity is dramatically different and this matters for translation. From the Kerns bioassay: 103 rats developed nasal SCC at 14.3 ppm versus 2 male mice at the same concentration. Mice reflexively reduce their minute ventilation on formaldehyde exposure — they literally breathe less of it — which is a dosimetry difference, not a mechanism difference.

VERIFIED quote — PMID:6871871 (Kerns 1983): "Squamous cell carcinomas were observed in the nasal cavities of 103 rats (52 females and 51 males) and 2 male mice exposed to 14.3 ppm and in 2 rats (one male and one female) exposed to 5.6 ppm of formaldehyde gas."

VERIFIED quote — PMID:6871871: "Significant formaldehyde-induced lesions were restricted to the nasal cavity and proximal trachea. The distribution and severity of these lesions were concentration dependent."

That "restricted to the nasal cavity and proximal trachea" line is the strongest available support for the portal-of-entry principle, and it's verified — use it.

Natural/veterinary disease: Formalin is widely used in aquaculture as a parasiticide, so overdose toxicity in fish is a real veterinary entity. A published case of formalin intoxication in a 13-year-old Thoroughbred gelding (survived) exists in Equine Veterinary Journal 2024 ⚠️ UNVERIFIED — find the PMID; it would make a nice evidence_source: MODEL_ORGANISM item per your veterinary edge-case rule. Formaldehyde is also used in agricultural fumigation and feed preservation, so livestock exposure occurs.

OMIA: I found no naturally occurring Mendelian ADH5/ALDH2 clearance disorder catalogued in animals. Worth an explicit "not found" rather than silence.

Comparative/evolutionary: ADH5/GSNOR is deeply conserved — bacteria through mammals. Pontel's framing ("counteracted in mammals by a conserved protection mechanism") captures it. That conservation is itself an argument that endogenous formaldehyde has been a persistent selective pressure for a very long time; the drain evolved because the sink was always filling.

Zoonotic potential: N/A — it's a chemical.

15. Model Organisms

Genetic models (the crown jewels of this entry)

Model	Genotype	Phenotype recapitulated	Fidelity
`Adh5^-/-` mouse	Single tier-1 KO	Accumulates formaldehyde-DNA adducts; relatively mild alone	MODERATE — establishes the adduct claim
`Adh5^-/-Fancd2^-/-` mouse	Clearance + repair double KO	HSC depletion → bone marrow failure; hepatocyte and nephron karyomegaly and dysfunction; all animals eventually develop fatal malignancies. BMT rescued hematopoiesis and nephron function.	HIGH for the genotoxic arm
`Adh5^-/-Aldh2^E506K/E506K` mouse	The AMeD genocopy (E506K = mouse equivalent of human E504K)	Short lifespan, dwarfism, hematopoietic failure	HIGH for AMeD
`Aldh2^-/-Adh5^-/-` mouse (Dingler 2020)	Two-clearance-system KO	Greatly shortened lifespan, leukemia ⚠️ UNVERIFIED — PMID:33147438, fetch the abstract	—
Patient-derived iPSC (Mu 2021)	`ADH5^-/-` + `ALDH2*2`	Defective hematopoietic expansion, increased DNA damage; partial rescue by ALDH2 agonist C1	HIGH — human genetic background
Chicken DT40	`ADH5`/FA-pathway mutants	Formaldehyde hypersensitivity; used in Burgos-Barragan's folate work	MODERATE (IN_VITRO)

For dismech: these belong in animal_models: (not experimental_models:) with modeled_mechanisms links. The Adh5^-/-Fancd2^-/- mouse is a RECAPITULATES link to the HSC-depletion node with two or three good readouts. The iPSC model goes in experimental_models: with a RESCUES link for the C1 arm — that's a textbook use of the RESCUES relationship.

Induced/exposure models

F344 rat inhalation bioassay (the Kerns design: 0 / 2.0 / 5.6 / 14.3 ppm, 6 h/day, 5 d/wk, 24 months) — the canonical carcinogenicity model
B6C3F1 mouse inhalation (much less sensitive)
Nonhuman primate ¹³CD₂-formaldehyde inhalation — the definitive exogenous-vs-endogenous adduct discrimination
Rat/mouse oral gavage formalin models for corrosive injury
In vitro: A549, BEAS-2B, primary nasal epithelial cells, CD34+ HSPCs, lymphoblastoid lines

Model limitations — curate these, don't hide them

Rodent nasal dosimetry ≠ human. Obligate nose-breathing rats vs oronasal humans; tumor site differs (rat nasal cavity vs human nasopharynx). → HUMAN_MODEL_MISMATCH.
No animal model reproduces formaldehyde-induced leukemia by inhalation. The leukemia signal is epidemiologic; the mouse leukemia comes from genetic clearance failure (endogenous formaldehyde), not inhalation. Conflating those two is the single most common error in this literature. → HUMAN_MODEL_MISMATCH + KNOWLEDGE_GAP.
Rat tumors occur only at frankly cytotoxic concentrations, well above human occupational exposure — the low-dose extrapolation is genuinely contested.
Genetic KO models model the endogenous disease; they establish mechanism plausibility for the exposure disease but are not exposure models.
No good animal model of the acute corrosive ingestion syndrome.

Resources: MGI (Adh5, Aldh2, Fancd2 alleles), IMPC, Alliance of Genome Resources, JAX/IMSR strain repositories, RGD, Cellosaurus (DT40), ZFIN.

Curation notes for the dismech entry

A few things specific to your pipeline, since that's the point of this:

Module conformance candidates. This entry can plausibly declare parallel conforms_to against several existing modules — worth checking each rather than building a from-scratch graph: - fibrotic_response — the late stricture/gastric-outlet-obstruction arm - genome_instability_mutation — the DPC/adduct → mutator-phenotype arm (this looks like a strong fit) - myelosuppression — HSC depletion → cytopenias, though that module is framed for cytotoxic therapy, so read it before wiring - tumor_promoting_inflammation — the chronic nasal inflammation + regenerative proliferation → SCC route - drug_induced_nephrotoxicity — probably NOT; the renal injury here is genotoxic/karyomegalic rather than the dose-dependent ATN pattern that module models

A new module might be warranted: reactive aldehyde clearance failure — ADH5/ALDH2 two-tier clearance → aldehyde accumulation → DNA/protein crosslinks → repair saturation → stem cell attrition. That pattern recurs across formaldehyde, acetaldehyde/alcohol, and Fanconi anemia, so it has the recurrence property a module needs. Worth raising with Harry before building.

Evidence discipline flags: - PMID:7265415 has NO ABSTRACT. Do not quote it. Cite in notes only. - The Zhang forensic "blood fixation" mechanism is one case's hypothesis — supports: PARTIAL plus a discussions: entry, not a confident causal node. - The formaldehyde→leukemia link needs mechanistic_hypotheses with competing groups, not a single asserted chain. - Rodent quotes are evidence_source: MODEL_ORGANISM and must not be the sole support for a human phenotype. - Everything I marked ⚠️ UNVERIFIED needs just fetch-reference + just count-verified-snippets before it goes near a PR.

Verified-quote inventory (safe to curate, subject to your own cache check): PMID:10962510 · PMID:35394178 · PMID:32686516 · PMID:26412304 · PMID:6871871 · PMID:28813411 · PMID:33355142.

Needs fetching: PMID:38614309 (paraphrased) · PMID:33512438 (fragments only) · PMID:33147438 (not fetched) · PMID:30701286 (not fetched) · the equine formalin case · the ICM formalin case series · the corrosive-ingestion meta-analysis.

Sources

Reference Validation

Checked with linkml-reference-validator 0.2.1.

Outcome	Count
References checked	20
Resolved	20
Unresolved (possible confabulation)	0
Unverifiable	0

All extracted references resolved successfully.

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Mappings

Definitions

Subtypes

Mechanistic Hypotheses

Discussions and Knowledge Gaps

Pathophysiology

Pathograph

Phenotypes

Genetic Associations

Medical Actions

Environmental Factors

Biochemical Markers

Diagnosis

Prevalence

Differential Diagnoses

Experimental Models

Animal Models

Source YAML

References & Deep Research

Deep Research

Formaldehyde Poisoning — Research Report

0. Framing: this is three diseases wearing one coat

1. Disease Information

Overview

Identifiers

Synonyms

Data provenance character

2. Etiology

Primary causal factor

Environmental / exposure risk factors

Genetic risk factors — this is the good part

Protective factors

Gene–environment interaction

3. Phenotypes

A. Acute inhalation (irritant syndrome) — onset minutes, course acute/self-limited if exposure ends

B. Acute ingestion (corrosive + systemic) — onset minutes to hours, severe, often fatal

C. Chronic exposure

D. Inherited clearance failure (AMeD syndrome) — separate entity, childhood onset

Quality of life

4. Genetic / Molecular Information

Genes

Key variants

Functional consequence

Epigenetics

Chromosomal

5. Environmental Information

6. Mechanism / Pathophysiology

Chain A — Corrosive protein crosslinking (local injury)

Chain B — Metabolism to formate → acidosis (systemic injury)

Chain C — Genotoxicity → stem cell attrition and carcinogenesis

Chain D — Immune sensitization

Chain E — The salvage arm (why this isn't purely destructive)

Suggested ontology terms (⚠️ all need OAK verification)

7. Anatomical Structures Affected

8. Temporal Development

9. Inheritance and Population

Epidemiology of poisoning

Corrosive-ingestion outcome benchmarks (⚠️ ALL-CORROSIVE, NOT FORMALIN-SPECIFIC)

Lethal dose

For AMeD syndrome

10. Diagnostics

The headline: there is no useful clinical formaldehyde assay.

Laboratory

Imaging / endoscopy

Functional / other

Genetic testing (for AMeD, not for poisoning)

Differential diagnosis

Screening

11. Outcome / Prognosis

12. Treatment

Acute ingestion

Acute inhalation

Chronic

AMeD syndrome

Pharmacogenomics

Clinical trials

13. Prevention

14. Other Species / Natural Disease