Folliculitis

Complex MONDO:0006552 Pathograph 25 dermatitis disorder of pilosebaceous unit

Folliculitis is inflammation of hair follicles with infectious and noninfectious etiologies, typically presenting with follicular papules, papulopustules, and pruritus.

Mappings

Definitions

Inheritance

Genes

Models

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Classifications

Harrison's Chapter

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Subtypes

etiologic

Staphylococcal folliculitis

Superficial bacterial folliculitis in which Staphylococcus aureus is the predominant causative organism.

Show evidence (2 references)

PMID:22639852 SUPPORT Human Clinical

"There are various infectious and non-infectious causes of folliculitis, and the most common causative agent is Staphylococcus aureus."

Supports staphylococcal folliculitis as the most common etiologic subtype.

PMID:15482221 SUPPORT Human Clinical

"S. aureus is one of the most common causes of skin infection, giving rise to folliculitis, furunculosis, carbuncles, ecthyma, impetigo, cellulitis and abscesses."

Independent review evidence supports staphylococcal folliculitis within the common S. aureus skin-infection spectrum.

Malassezia folliculitis

Lipophilic yeast-associated folliculitis presenting with pruritic papules and pustules.

Show evidence (1 reference)

PMID:36912427 SUPPORT Human Clinical

"Malassezia folliculitis appears when the benign colonization of the hair follicles, by the Malassezia yeasts, becomes symptomatic with pruritic papules and pustules."

Supports Malassezia as a clinically distinct etiologic subtype.

Demodex-associated folliculitis

Folliculitis associated with Demodex mite colonization and increased histologic inflammation.

Show evidence (1 reference)

PMID:8989930 SUPPORT Human Clinical

"Demodex mites were found in 42% of follicles with inflammation, but in just 10% of the follicles without inflammation."

Supports a Demodex-associated folliculitis subtype with inflammatory enrichment.

exposure associated

Pseudomonas hot-tub folliculitis

Water-exposure-associated folliculitis caused by Pseudomonas aeruginosa after contaminated hot-tub or spa use.

Show evidence (1 reference)

PMID:6402527 SUPPORT Human Clinical

"Pseudomonas folliculitis resulting from the use of spa pools, whirlpools, and hot tubs is a newly described disease that typically develops 8 to 48 hours after exposure in a contaminated facility."

Defines a distinct exposure-associated pseudomonal subtype.

treatment associated

Gram-negative folliculitis

Folliculitis caused by gram-negative rods, commonly emerging after prolonged broad-spectrum antibiotic therapy in acne/rosacea contexts.

Show evidence (1 reference)

PMID:10321942 SUPPORT Human Clinical

"Gram-negative folliculitis is an infection with gram-negative rods that most often occurs as a complication of prolonged broad-spectrum antibiotic therapy in patients suffering from acne and rosacea."

Supports gram-negative folliculitis as a treatment-associated subtype.

immunologic

HIV-associated eosinophilic folliculitis

Culture-negative chronic pruritic folliculitis with eosinophilic inflammatory pattern in advanced HIV.

Show evidence (1 reference)

PMID:1671328 SUPPORT Human Clinical

"These observations demonstrate that HIV-associated eosinophilic folliculitis is a unique HIV-related cutaneous disorder that is characterized by a culture-negative, chronic, pruritic folliculitis and a characteristic histopathologic picture."

Supports a distinct HIV-associated eosinophilic subtype.

clinical phenotype

Folliculitis decalvans

Chronic neutrophilic scarring folliculitis of the scalp with recurrent inflammation and progressive alopecia.

Show evidence (2 references)

PMID:36716709 SUPPORT Human Clinical

"BACKGROUND: Folliculitis decalvans (FD) is a rare primary neutrophilic scarring alopecia whose etiology has not been completely elucidated yet."

Supports folliculitis decalvans as a clinically distinct scarring subtype.

PMID:18715292 SUPPORT Human Clinical

"Folliculitis decalvans is classified as primary neutrophilic cicatricial alopecia and predominantly occurs in middle-aged adults."

Adds independent subtype-level characterization of FD as primary neutrophilic cicatricial alopecia.

treatment induced

EGFR inhibitor-induced folliculitis

Folliculitis developing during anti-EGFR therapy, including chronic and scarring inflammatory forms in susceptible patients.

Show evidence (1 reference)

clinicaltrials:NCT06818058 SUPPORT Human Clinical

"A Phase II, multicentric, randomized, double-blind, placebo-controlled, parallel- group trial to confirm the good safaty profile and to explore the preventive effect of topically applied TAR-0520 gel on folliculitis developed in metastatic colorectal cancer (mCRC) patients treated with..."

Supports anti-EGFR-therapy-associated folliculitis as a clinically recognized treatment-induced subtype.

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Pathophysiology

Staphylococcus aureus follicular colonization

S. aureus colonization of hair follicles is a common proximal trigger for infectious folliculitis.

hair follicle link

Show evidence (1 reference)

PMID:22639852 SUPPORT Human Clinical

"There are various infectious and non-infectious causes of folliculitis, and the most common causative agent is Staphylococcus aureus."

Supports S. aureus as an upstream and common etiologic mechanism.

Staphylococcal virulence factor activity

S. aureus expresses cytolytic, superantigenic, and immune-evasion factors that enable progression from colonization to tissue-level inflammation.

Show evidence (1 reference)

DOI:10.3390/antibiotics12030557 SUPPORT Human Clinical

"In order to cause skin infections, S. aureus employs a host of virulence factors including cytolytic proteins, superantigenic factors, cell wall-anchored proteins, and molecules used for immune evasion."

Supports a biomolecular virulence stage in staphylococcal folliculitis.

Keratinocyte innate immune activation

Keratinocytes act as early epithelial sentinels and initiate innate immune responses after bacterial challenge.

keratinocyte link

response to bacterium link

Show evidence (1 reference)

DOI:10.3390/antibiotics12030557 SUPPORT Human Clinical

"The immune response to S. aureus SSTIs involves initial responders such as keratinocytes and neutrophils, which are supported by dendritic cells and T-lymphocytes later during infection."

Supports keratinocyte participation as an early cellular event in skin infection pathophysiology.

Neutrophil recruitment and activation

Neutrophils are recruited and activated, amplifying follicular inflammatory injury.

neutrophil link

neutrophil activation link

Show evidence (1 reference)

DOI:10.3390/antibiotics12030557 SUPPORT Human Clinical

"The immune response to S. aureus SSTIs involves initial responders such as keratinocytes and neutrophils, which are supported by dendritic cells and T-lymphocytes later during infection."

Supports neutrophil-centric immune amplification in staphylococcal folliculitis mechanisms.

Acute suppurative follicular inflammation

Follicular inflammation progresses to acute suppuration with histologic evidence of neutrophil-rich tissue injury.

inflammatory response link

Show evidence (1 reference)

PMID:6402527 SUPPORT Human Clinical

"Skin biopsies showed an acute, suppurative folliculitis and dermal abscess formation."

Histopathology confirms the suppurative inflammatory stage.

Non-staphylococcal microbial follicular colonization

Gram-negative bacterial, fungal, parasitic, and viral pathogens can also colonize follicles and converge on inflammatory papulopustular disease.

hair follicle link

Show evidence (1 reference)

PMID:22639852 SUPPORT Human Clinical

"In addition, several Gram-negative bacterial, fungal, parasitic, and viral pathogens can cause follicular papules and pustules."

Supports a pathogen-diverse upstream entry point into folliculitis pathophysiology.

Prolonged broad-spectrum antibiotic exposure in acne or rosacea

Extended broad-spectrum antibiotic exposure can create conditions that favor gram-negative follicular infection.

Show evidence (1 reference)

PMID:10321942 SUPPORT Human Clinical

Supports prolonged antibiotic exposure as an upstream event in gram-negative folliculitis.

Gram-negative follicular overgrowth and infection

Gram-negative organisms including Klebsiella, Escherichia coli, Enterobacter, and Proteus can overgrow and infect follicles.

hair follicle link

Show evidence (1 reference)

PMID:10321942 SUPPORT Human Clinical

"The gram-negative organisms most frequently cultivated from nares, facial skin, and pustules were Klebsiella spp., Escherichia coli, Enterobacter spp., and Proteus spp."

Supports a discrete pathogen-overgrowth stage in gram-negative folliculitis.

Demodex follicular colonization

Demodex mites are present in a subset of follicles and are associated with inflammatory follicular histopathology.

hair follicle link

Show evidence (1 reference)

PMID:8989930 SUPPORT Human Clinical

"Demodex mites were found in 42% of follicles with inflammation, but in just 10% of the follicles without inflammation."

Supports Demodex colonization as a candidate upstream event in follicular inflammation.

Demodex-associated follicular inflammation

Follicles containing Demodex mites frequently show inflammatory changes, supporting a mite-associated inflammatory folliculitis pathway.

Show evidence (1 reference)

PMID:8989930 SUPPORT Human Clinical

"Eighty-three percent of follicles with Demodex showed inflammation."

Supports mite-associated follicular inflammation as a discrete pathophysiologic event.

Malassezia follicular colonization

Malassezia yeast exists as part of the normal follicular mycobiome before symptomatic disease develops.

hair follicle link

Show evidence (1 reference)

PMID:36912427 SUPPORT Human Clinical

"Malassezia is a lipophilic yeast that is a part of the human mycobiome."

Establishes baseline commensal follicular colonization by Malassezia.

Pathogenic Malassezia transition with virulence factor production

Host-agent interactions can drive Malassezia transition from commensal to pathogenic states with production of inflammatory virulence factors.

Show evidence (1 reference)

PMID:35751534 SUPPORT Human Clinical

"However, in certain conditions and individuals, it may transform into a pathogenic yeast with multiple associated dermatological disorders and various clinical manifestations."

Supports commensal-to-pathogenic transition in Malassezia disease biology.

Malassezia-associated follicular inflammation

Symptomatic Malassezia folliculitis manifests as inflammatory pruritic papulopustular follicular lesions.

Show evidence (1 reference)

PMID:36912427 SUPPORT Human Clinical

"Malassezia folliculitis appears when the benign colonization of the hair follicles, by the Malassezia yeasts, becomes symptomatic with pruritic papules and pustules."

Supports symptomatic inflammatory transition in Malassezia folliculitis.

Eosinophilic follicular inflammation in advanced HIV

In advanced HIV infection, a culture-negative eosinophilic folliculitis pattern can occur with chronic pruritic disease.

eosinophil link

Show evidence (1 reference)

PMID:1671328 SUPPORT Human Clinical

Defines an immunologic, eosinophilic folliculitis mechanism distinct from pyogenic bacterial disease.

Folliculitis decalvans follicular dysbiosis

Folliculitis decalvans exhibits a disease-associated shift in follicular bacterial community structure.

hair follicle link

Show evidence (1 reference)

PMID:36716709 SUPPORT Human Clinical

"CONCLUSION: FD hair follicles have a specific heterogenous follicular bacterial microbiota signature."

Supports the presence of subtype-specific follicular dysbiosis in folliculitis decalvans.

Impaired antibacterial cytokine response in folliculitis decalvans

Patients with folliculitis decalvans show reduced cytokine responses to bacterial stimulation.

Show evidence (3 references)

PMID:36716709 SUPPORT Human Clinical

"IL-10, TNF-α, and IL-6 levels were significantly decreased in patients after incubation with various strains of bacteria compared with controls."

Supports impaired antibacterial cytokine signaling as a mechanistic event in folliculitis decalvans.

clinicaltrials:NCT07268534 PARTIAL Human Clinical

"FD is a non-curable disease for which inflammatory pathways involving several cytokines as TNF, IL1β, IL8, TGFβ, IL12 and 23, could also play a role."

Trial rationale provides additional human-clinical support for cytokine pathway involvement in FD pathobiology.

PMID:18715292 SUPPORT Human Clinical

"Staphylococcus aureus and a deficient host immune response seem to play an important role in the development of this disfiguring scalp disease."

Supports host-immune dysfunction as a central mechanistic factor in FD pathogenesis.

Neutrophilic scarring follicular inflammation in folliculitis decalvans

Folliculitis decalvans is characterized by chronic neutrophilic follicular inflammation with scarring progression.

neutrophil link

Show evidence (2 references)

PMID:36716709 SUPPORT Human Clinical

"BACKGROUND: Folliculitis decalvans (FD) is a rare primary neutrophilic scarring alopecia whose etiology has not been completely elucidated yet."

Supports a distinct chronic neutrophilic scarring-inflammatory stage in FD.

PMID:18715292 SUPPORT Human Clinical

"Histology displays a mainly neutrophilic inflammatory infiltrate in early lesions and additionally lymphocytes and plasma cells in advanced lesions."

Adds direct histologic support for neutrophil-dominant early FD inflammation with chronic inflammatory progression.

EGFR pathway disruption in follicular stem-cell niche

EGFR pathway loss removes protective signaling in the follicular stem-cell niche and predisposes to inflammatory tissue injury.

Show evidence (1 reference)

PMID:39521937 SUPPORT Model Organism

"In this study, we demonstrated the protective role of hair follicle-specific epidermal growth factor receptor (EGFR) against scarring hair follicle destruction."

Supports loss of EGFR-mediated follicular protection as an initiating mechanistic event.

JAK-STAT1 pathway hypersensitivity in EGFR-deficient follicles

EGFR-deficient follicular cells develop heightened JAK-STAT1 signaling sensitivity.

Show evidence (1 reference)

PMID:39521937 SUPPORT Model Organism

"Mechanistically, disruption of EGFR signaling generated a cell-intrinsic hypersensitivity within the JAK-STAT1 pathway, which, synergistically with interferon gamma expressing CD8 T-cell and NK-cell-mediated inflammation, compromised the stem cell niche."

Supports JAK-STAT1 hypersensitivity as a distinct biomolecular event.

Interferon-γ CD8 T-cell and NK-cell inflammatory amplification

Interferon-γ-expressing CD8 T cells and NK cells amplify follicular inflammatory injury in EGFR-deficient settings.

Show evidence (1 reference)

PMID:39521937 SUPPORT Model Organism

Supports a lymphoid inflammatory amplification stage in EGFR inhibitor-associated folliculitis biology.

Stem-cell niche compromise and scarring follicle destruction

Compromised follicular stem-cell niche integrity and associated signaling changes culminate in scarring follicular injury.

Show evidence (1 reference)

PMID:39521937 SUPPORT Human Clinical

"Skin biopsies from EGFR inhibitor-treated and cicatricial alopecia patients revealed an active JAK-STAT1 signaling signature along with upregulation of antigen presentation and downregulation of key components of the EGFR pathway."

Supports endpoint follicular destruction biology with clinically relevant human tissue evidence.

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Histopathology

Acute suppurative folliculitis with dermal abscess formation

Biopsy in hot-tub folliculitis demonstrates acute neutrophilic suppurative folliculitis with dermal abscess formation.

Show evidence (1 reference)

PMID:6402527 SUPPORT Human Clinical

"Skin biopsies showed an acute, suppurative folliculitis and dermal abscess formation."

Direct histopathology evidence for suppurative inflammatory follicular injury in pseudomonal folliculitis.

Eosinophilic culture-negative chronic folliculitis pattern

HIV-associated eosinophilic folliculitis shows a characteristic histopathologic pattern with chronic pruritic culture-negative disease.

Show evidence (1 reference)

PMID:1671328 SUPPORT Human Clinical

Supports a distinct eosinophilic histopathologic pattern in HIV-associated folliculitis.

Demodex-associated follicular inflammation on histology

Follicles containing Demodex are frequently inflamed, supporting a mite-associated inflammatory histologic phenotype.

Show evidence (1 reference)

PMID:8989930 SUPPORT Human Clinical

"Eighty-three percent of follicles with Demodex showed inflammation."

Supports Demodex-associated inflammatory histopathologic findings.

Neutrophilic scarring alopecia pattern

Folliculitis decalvans is characterized histopathologically within the primary neutrophilic scarring alopecia spectrum.

Show evidence (2 references)

PMID:36716709 SUPPORT Human Clinical

"BACKGROUND: Folliculitis decalvans (FD) is a rare primary neutrophilic scarring alopecia whose etiology has not been completely elucidated yet."

Supports a chronic neutrophilic scarring histopathology context for folliculitis decalvans.

PMID:18715292 SUPPORT Human Clinical

"Histology displays a mainly neutrophilic inflammatory infiltrate in early lesions and additionally lymphocytes and plasma cells in advanced lesions."

Adds direct histopathology detail supporting mixed-stage inflammatory infiltrates in FD.

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Pathograph

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

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Phenotypes

Immune 1

Pustules Pustule (HP:0200039)

Show evidence (2 references)

PMID:22639852 SUPPORT Human Clinical

"In addition, several Gram-negative bacterial, fungal, parasitic, and viral pathogens can cause follicular papules and pustules."

Supports pustules as a core lesion type across infectious etiologies.

PMID:18715292 SUPPORT Human Clinical

"Clinically, the lesions present with follicular pustules, lack of ostia, diffuse and perifollicular erythema, follicular tufting, and, oftentimes, hemorrhagic crusts and erosions."

Provides subtype-specific clinical evidence for pustules in folliculitis decalvans.

Integument 3

Erythematous papules Erythematous papule (HP:0030350)

Show evidence (1 reference)

PMID:6402527 SUPPORT Human Clinical

"The eruption consists of pruritic papules, papulopustules, nodules, and urticarial lesions on the trunk and extremities."

Directly supports papular morphology and common distribution.

Pruritus Pruritus (HP:0000989)

Show evidence (1 reference)

PMID:6402527 SUPPORT Human Clinical

"The eruption consists of pruritic papules, papulopustules, nodules, and urticarial lesions on the trunk and extremities."

Confirms itch as a frequent symptom in symptomatic follicular eruptions.

Alopecia Alopecia (HP:0001596)

Show evidence (2 references)

PMID:41146582 SUPPORT Human Clinical

"Folliculitis decalvans (FD) and Tufted Hair Folliculitis (THF) present with recurrent episodes of follicular inflammation, pustules and crusting, predominantly of the scalp, leading to scarring alopecia."

Supports alopecia as a clinically important sequela in scarring folliculitis subtypes.

PMID:36716709 SUPPORT Human Clinical

"Folliculitis decalvans (FD) is a rare primary neutrophilic scarring alopecia whose etiology has not been completely elucidated yet."

Provides independent support that scarring alopecia is a defining phenotype of folliculitis decalvans.

Metabolism 1

Low-grade fever Fever (HP:0001945)

Show evidence (1 reference)

PMID:2307901 SUPPORT Human Clinical

"The condition is characterized by painful, papulopustular skin lesions often accompanied by low-grade fever, malaise, and other systemic symptoms."

Supports fever as a contextual phenotype in Pseudomonas-associated folliculitis.

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Treatments

Topical or systemic antibacterial therapy

Action: pharmacotherapy MAXO:0000058

Antibacterial pharmacotherapy is commonly used for presumed bacterial folliculitis.

Show evidence (2 references)

PMID:22639852 SUPPORT Human Clinical

"Therefore, topical and/or systemic antibacterial treatment is recommended, but this involves the risk of being misused for months or even years."

Review supports antibacterial treatment use while cautioning against prolonged empiric misuse.

DOI:10.3390/antibiotics12030557 SUPPORT Human Clinical

"Treatment for S. aureus SSTIs is usually oral therapy, with parenteral therapy reserved for severe presentations; it ranges from cephalosporins and penicillin agents such as oxacillin, which is generally used for methicillin-sensitive S. aureus (MSSA), to vancomycin for methicillin-resistant S...."

Adds contemporary treatment-stratification evidence for staphylococcal folliculitis-spectrum infections.

Topical and systemic antifungal therapy for Malassezia folliculitis

Action: pharmacotherapy MAXO:0000058

Ketoconazole cream and oral itraconazole are both effective options for Malassezia-associated disease.

Show evidence (2 references)

PMID:27581777 SUPPORT Human Clinical

"Treatment consisted of topical application of 2% ketoconazole cream or 100 mg oral itraconazole based on symptom severity and patients' preferences."

Documents real-world topical and oral antifungal regimens.

PMID:27581777 SUPPORT Human Clinical

"The results were "improved" and the treatment was "effective" in all patients."

Supports clinical effectiveness of both antifungal strategies in this cohort.

Combination therapy for folliculitis decalvans/tufted hair folliculitis

Action: pharmacotherapy MAXO:0000058

Combination regimens may provide better and longer responses than antibiotic monotherapy in scarring folliculitis subtypes.

Show evidence (3 references)

PMID:41146582 SUPPORT Human Clinical

"Combination therapy with systemic antibiotics, topical, local and/or other systemic agents may provide the best outcome and longest DoE for FD/THF patients, with a greater role for biologic agents and laser therapy in their management."

Systematic review supports multimodal treatment strategy for chronic scarring folliculitis variants.

PMID:29864465 SUPPORT Human Clinical

"Treatment with rifampicin and clindamycin, tetracyclines, and intralesional steroids was the most effective."

Multicenter long-term follow-up study provides specific evidence for effective combination regimens in folliculitis decalvans.

clinicaltrials:NCT07268534 SUPPORT Human Clinical

"Short-term efficacy rate of antibiotics is around 50-60%, but unfortunately, recurrences/relapses are occurring 5 to 7 months on average after stopping antibiotics, requiring their reintroduction/long-term use and potentially less efficacy/ecological harms."

Supports limitations of antibiotic-only strategies and the need for alternative or adjunctive management approaches in FD.

Adjunctive anti-inflammatory/phototherapy for HIV-associated eosinophilic folliculitis

Action: pharmacotherapy MAXO:0000058

Symptom-directed therapies such as UVB and topical corticosteroids can improve HIV-associated eosinophilic folliculitis.

Show evidence (1 reference)

PMID:1671328 SUPPORT Human Clinical

"A clinical response was noted to astemizole, to ultraviolet light in the B range, and to topical clobetasol propionate."

Supports specific adjunctive therapies in eosinophilic folliculitis context.

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Environmental Factors

Contaminated recreational water exposure

Exposure to inadequately disinfected hot tubs/spa pools can trigger Pseudomonas folliculitis.

Show evidence (1 reference)

PMID:6402527 SUPPORT Human Clinical

"Pseudomonas folliculitis resulting from the use of spa pools, whirlpools, and hot tubs is a newly described disease that typically develops 8 to 48 hours after exposure in a contaminated facility."

Supports contaminated water exposure as an environmental trigger.

Advanced HIV immunosuppression

Low CD4 counts are associated with eosinophilic folliculitis in HIV infection.

Show evidence (1 reference)

PMID:1671328 SUPPORT Human Clinical

"Of special importance, because it is associated with CD4 counts of less than 250 to 300 cells per cubic millimeter, eosinophilic folliculitis appears to be an important clinical marker of HIV infection and, particularly, of patients at increased risk of developing opportunistic infections."

Supports severe HIV-associated immunosuppression as a major risk context.

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Differential Diagnoses

Conditions with similar clinical presentations that must be differentiated from Folliculitis:

Acne MONDO:0011438

Overlapping Features Acne and folliculitis both produce papulopustular lesions but differ in comedones and typical distribution patterns.

Distinguishing Features

Acne typically has comedones and facial/truncal sebaceous distribution.
Folliculitis often has follicle-centered lesions and may be linked to specific infectious exposures.

Show evidence (1 reference)

PMID:12113648 SUPPORT Human Clinical

"Localized pustular eruptions are seen on the hands and feet in adults with pustulosis palmaris et plantaris and acrodermatitis continua (both of which may be variants of psoriasis); on the face in patients with acne vulgaris, rosacea, and perioral dermatitis; and on the trunk and/or extremities..."

The abstract lists acne and folliculitis as overlapping pustular disorders with different common distributions.

Furunculosis MONDO:0100595

Overlapping Features Furunculosis represents deeper suppurative follicular infection than superficial folliculitis.

Distinguishing Features

Furunculosis generally presents as deeper, more painful boils/abscesses.
Folliculitis is usually more superficial and papulopustular.

Show evidence (2 references)

DOI:10.1159/000499184 SUPPORT Human Clinical

"The most frequent <i>S. aureus</i> infections include impetigo, folliculitis, furuncles, furunculosis, abscesses, hidradenitis suppurativa, and mastitis."

Places folliculitis and furunculosis within overlapping staphylococcal skin infection spectrum requiring clinical differentiation.

PMID:15482221 SUPPORT Human Clinical

"S. aureus is one of the most common causes of skin infection, giving rise to folliculitis, furunculosis, carbuncles, ecthyma, impetigo, cellulitis and abscesses."

Provides additional spectrum-based evidence supporting furunculosis as a key differential within staphylococcal follicular infections.

Hidradenitis suppurativa MONDO:0006559

Overlapping Features Hidradenitis has chronic nodules/sinus tracts in intertriginous sites and can mimic recurrent follicular infection.

Distinguishing Features

Typical involvement of apocrine/intertriginous regions with sinus tracts and scarring.
Folliculitis usually involves superficial follicular papules and pustules without chronic sinus formation.

Show evidence (1 reference)

DOI:10.1159/000499184 SUPPORT Human Clinical

"The most frequent <i>S. aureus</i> infections include impetigo, folliculitis, furuncles, furunculosis, abscesses, hidradenitis suppurativa, and mastitis."

Supports hidradenitis suppurativa as a clinically overlapping condition in staphylococcal-spectrum skin disease discussions.

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Related Datasets

Spatial transcriptomics reveals dysfunctional lipid metabolism and abnormal pilosebaceous differentiation in acne vulgaris geo:GSE301280

Spatial transcriptomics dataset in human acne lesions with an associated experimental component showing reduced pustule formation in a mouse model of high-fat-diet-induced folliculitis.

human SPATIAL TRANSCRIPTOMICS n=24

Conditions: healthy skin non-lesional acne skin comedonal acne skin pustular acne skin

Included as a related pilosebaceous inflammation dataset with explicit folliculitis-model context.

Show evidence (2 references)

GEO:GSE301280 SUPPORT Human Clinical

"Here, we performed spatial transcriptomics on healthy, non-lesional, comedonal, and pustular acne skin using a custom panel targeting sebaceous differentiation, lipid metabolism, and retinoid signaling pathways."

Supports this as a human pilosebaceous spatial transcriptomics resource relevant to follicular inflammatory biology.

GEO:GSE301280 SUPPORT Model Organism

"Finally, we demonstrate that an AP-1 inhibitor, T-5224, strongly downregulates FABP5 in human keratinocytes and reduces pustule formation in a mouse model of high fat diet-induced folliculitis."

The same GEO summary includes a linked mouse folliculitis model result, increasing disease relevance.

JAK-STAT1 as therapeutic target for EGFR deficiency-associated inflammation and scarring alopecia (RNA-seq of HFSC) geo:GSE273571

Bulk RNA-seq of mouse hair follicle stem cells from EGFR-deficient versus wild-type conditions in a model used to study chronic folliculitis and scarring alopecia.

house mouse BULK RNA SEQ n=6

Conditions: hair follicle stem cells, EGFR-deficient model hair follicle stem cells, wild type

PMID:39521937

Show evidence (2 references)

GEO:GSE273571 SUPPORT Model Organism

"Mechanistically, disruption of EGFR signalling generated a cell-intrinsic hypersensitivity within the JAK-STAT1 pathway, which, synergistically with interferon gamma expressing CD8 T-cell and NK-cell-mediated inflammation, compromised the stem cell niche."

Supports mechanistic transcriptomic interrogation of EGFR-driven follicular inflammatory injury.

GEO:GSE273571 SUPPORT Model Organism

"Our findings offer molecular insights and present a mechanism-based therapeutic strategy for addressing chronic folliculitis associated with EGFR-inhibitor anti-cancer therapy and cicatricial alopecia."

Explicitly links this dataset context to chronic folliculitis biology.

JAK-STAT1 as therapeutic target for EGFR deficiency-associated inflammation and scarring alopecia (scRNA-seq) geo:GSE273572

Single-cell RNA-seq of EGFR-deficient mouse epidermal context generated to characterize follicular immune-epithelial dysregulation in scarring folliculitis biology.

house mouse SINGLE CELL RNA SEQ n=1

Conditions: EGFR-deficient epidermal context

PMID:39521937

Show evidence (2 references)

GEO:GSE273572 SUPPORT Model Organism

"In this study, we demonstrated the protective role of hair follicle-specific epidermal growth factor receptor (EGFR) against scarring hair follicle destruction."

Supports the dataset's central focus on follicle-protective EGFR signaling in a scarring folliculitis model.

GEO:GSE273572 SUPPORT Model Organism

"Notably, a case study of folliculitis decalvans, characterized by progressive hair loss, scaling and perifollicular erythema, demonstrated successful treatment with JAK1/2 inhibition."

Provides direct folliculitis decalvans clinical linkage for interpretation of model-derived single-cell signatures.

Adverse Events of anti-EGFR Therapy are Triggered by Hair Eruption and Commensal Skin Microbiota geo:GSE119376

Expression profiling of primary human epidermal keratinocytes under EGFR inhibition, describing barrier dysfunction and chronic folliculitis-related inflammatory programs.

human MICROARRAY n=12

Conditions: keratinocytes, EGFR inhibition keratinocytes, control

Show evidence (2 references)

GEO:GSE119376 SUPPORT In Vitro

"In the absence of EGFR, opening of the follicular ostia during hair eruption allows invasion of commensal microbiota aggravating barrier disruption and initiating an additional Th1 and Th17 response."

Supports EGFR-perturbation-associated follicular barrier and immune dysregulation mechanisms.

GEO:GSE119376 SUPPORT In Vitro

"Chronic folliculitis leads to Staphylococcus aureus dominated dysbiosis, further exacerbating inflammation and expanding barrier defects."

Directly supports chronic folliculitis-associated dysbiosis and inflammatory amplification.

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Clinical Trials

NCT06307223 PHASE_IV COMPLETED

Interventional study evaluating topical 30% supramolecular salicylic acid plus active zinc in Malassezia folliculitis, including recurrence-relevant follow-up over 12 weeks.

Target Phenotypes: pustule ↗ pruritus ↗

Show evidence (1 reference)

clinicaltrials:NCT06307223 SUPPORT Human Clinical

"In the present study, investigators evaluated the clinical efficacy of topical application of supramolecular salicylic acid in combination with zinc pyrithione for the treatment and prevention of Malassezia folliculitis recurrence."

Supports direct trial relevance to Malassezia folliculitis treatment and recurrence prevention.

NCT06818058 PHASE_II RECRUITING

Randomized placebo-controlled multicenter phase II trial of topical TAR-0520 gel for prevention of EGFR inhibitor-associated folliculitis in metastatic colorectal cancer.

Target Phenotypes: erythematous papule ↗ pustule ↗

Show evidence (1 reference)

clinicaltrials:NCT06818058 SUPPORT Human Clinical

Supports an ongoing controlled trial focused on prevention of EGFR inhibitor-associated folliculitis.

NCT02157688 NOT_APPLICABLE COMPLETED

Comparative bacteriological study in folliculitis decalvans designed to clarify the role of Staphylococcus aureus in disease pathophysiology.

Target Phenotypes: alopecia ↗ pustule ↗

Show evidence (1 reference)

clinicaltrials:NCT02157688 SUPPORT Human Clinical

"The pathophysiology is poorly understood, Staphylococcus aureus (SA) appears to play a role, never previously studied, and the study will attempt to clarify it."

Supports trial relevance to microbial mechanisms in folliculitis decalvans, a clinically important folliculitis subtype.

NCT07268534 PHASE_II NOT_RECRUITING

Adaptive phase II/III clinical trial evaluating biologic strategies for folliculitis decalvans, motivated by limited durability of antibiotic-only treatment and cytokine-pathway hypotheses.

Target Phenotypes: alopecia ↗ pustule ↗

Show evidence (2 references)

clinicaltrials:NCT07268534 SUPPORT Human Clinical

Supports unmet-need rationale for intervention trials beyond antibiotics in FD.

clinicaltrials:NCT07268534 SUPPORT Human Clinical

"FD is a non-curable disease for which inflammatory pathways involving several cytokines as TNF, IL1β, IL8, TGFβ, IL12 and 23, could also play a role."

Supports cytokine-targeted biologic trial rationale in FD.

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Literature Summaries

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Disease Pathophysiology Research Template

Edison Scientific Literature 30 citations 2026-03-01T18:02:17.542643

Question: You are an expert researcher providing comprehensive, well-cited information.

Provide detailed information focusing on: 1. Key concepts and definitions with current understanding 2. Recent developments and latest research (prioritize 2023-2024 sources) 3. Current applications and real-world implementations 4. Expert opinions and analysis from authoritative sources 5. Relevant statistics and data from recent studies

Format as a comprehensive research report with proper citations. Include URLs and publication dates where available. Always prioritize recent, authoritative sources and provide specific citations for all major claims.

Disease Pathophysiology Research Template

Target Disease

Disease Name: Folliculitis
MONDO ID: (if available)
Category: Complex

Research Objectives

Please provide a comprehensive research report on the pathophysiology of Folliculitis. Focus on the molecular and cellular mechanisms underlying disease progression.

Required Information

1. Core Pathophysiology

What are the primary pathophysiological mechanisms?
What molecular pathways are dysregulated?
What cellular processes are affected?

2. Key Molecular Players

Genes/Proteins: Which genes are causally involved or implicated?
Chemical Entities: What metabolites, drugs, or small molecules are relevant?
Cell Types: Which cell types are primarily affected?
Anatomical Locations: Which tissues/organs are involved?

3. Biological Processes (for GO annotation)

What biological processes (GO terms) are disrupted?
Consider: signaling pathways, metabolic processes, cellular responses, transport, etc.

4. Cellular Components

Where in the cell do key processes occur?
Consider: organelles, membrane compartments, extracellular space, etc.

5. Disease Progression

What is the sequence of events from initial trigger to clinical manifestation?
Are there distinct stages or phases?

6. Phenotypic Manifestations

What are the key clinical phenotypes?
How do they relate to the underlying mechanisms?

Citation Requirements

Cite primary literature (PMID preferred) for all mechanistic claims
Prioritize recent reviews and landmark papers
Include direct quotes where possible to support key statements

Output Format

Structure your response as a narrative that could be used to populate a disease knowledge base entry with: - Pathophysiology description - Gene/protein annotations with ontology terms (HGNC, GO) - Phenotype associations (HP terms) - Cell type involvement (CL terms) - Anatomical locations (UBERON terms) - Chemical entities (CHEBI terms) - Evidence items with PMIDs

Comprehensive Research Report: Folliculitis Pathophysiology (Molecular & Cellular Mechanisms)

Scope note and definition

Folliculitis is a clinicopathologic syndrome defined by inflammation centered on the hair follicle (pilosebaceous unit), presenting as follicular papules and/or pustules. In practice, “folliculitis” includes multiple entities with distinct etiologies and immune programs (e.g., bacterial folliculitis/furunculosis, Malassezia folliculitis, eosinophilic pustular folliculitis/Ofuji disease, and folliculitis decalvans), which share a folliculocentric inflammatory pattern but differ in triggers, dominant effector cells, and risk of scarring.

Current understanding: across subtypes, folliculitis emerges when (i) follicular barrier/immune homeostasis is perturbed (e.g., occlusion, altered keratinocyte differentiation, immunosuppression), enabling (ii) microbial overgrowth and/or dysbiosis or noninfectious inflammatory triggers, which then (iii) activate epithelial innate immune programs and (iv) recruit granulocytes (neutrophils or eosinophils) that create pustules and can destroy follicular epithelium. Malassezia folliculitis highlights a type-17 program (IL‑23/IL‑17 axis), eosinophilic pustular folliculitis is typically type-2 skewed (eosinophils, PGD2–CRTH2), and folliculitis decalvans is a neutrophilic scarring alopecia with microbiome/immune dysregulation and frequent Staphylococcus aureus associations. (martinezortega2024malasseziafolliculitispathogenesis pages 4-5, morenoarrones2023folliculitisdecalvanshas pages 8-8, li2023clinicalandpathological pages 5-6, nowaczyk2023egfrinhibitorinducedfolliculitis pages 3-5)

Disease identifiers

A MONDO identifier was not retrieved in the accessible evidence for “folliculitis” as a parent concept in this run.

1) Core pathophysiology

1.1 Bacterial folliculitis and furunculosis (S. aureus-centric)

Trigger/initiating event. Bacterial folliculitis commonly follows microinjury, maceration, friction, shaving, or occlusion that enables follicular invasion by bacteria; deep folliculitis/furunculosis represents follicle rupture with dermal/hypodermal abscess formation.

Microbe and virulence determinants. Staphylococcus aureus employs cytolytic toxins, immune evasion, and abscess-promoting factors in follicular infections. In a highly cited 2023 review, Panton–Valentine leukocidin (PVL) is described as “a cytotoxic virulence factor” with PVL positivity rates of 40–90% in furunculosis. (linz2023clinicalimpactof pages 3-5) S. aureus alpha-hemolysin (Hla) contributes to epithelial injury; Hla “induces keratinocyte necrosis” and is “required for infection in keratinocytes,” and Hla binds ADAM10 and can disrupt epithelial adhesion via E‑cadherin cleavage. (linz2023clinicalimpactof pages 10-11, linz2023clinicalimpactof pages 5-7)

Innate immune recognition and cytokine programs. Cutaneous pattern-recognition receptor (PRR) signaling contributes to early inflammation. The same review notes PRRs “including TLR2 and NOD2,” and that NOD2 loss in models increases bacterial burden and NF‑κB activity. (linz2023clinicalimpactof pages 10-11) The host response is initially neutrophil-dominant with inflammatory mediators (e.g., IL‑6, IL‑1β, chemokines) and later shifts toward IL‑17A/F–associated programs. (linz2023clinicalimpactof pages 10-11)

Cellular processes affected. Key processes include keratinocyte activation, neutrophil recruitment/activation (including neutrophil extracellular traps, NETs), abscess organization, and (in deep disease) tissue destruction and scarring. (linz2023clinicalimpactof pages 10-11, linz2023clinicalimpactof pages 3-5)

Quantitative recent context (SSTIs as a folliculitis-adjacent umbrella). Recurrent SSTIs occur in ~16–19% of patients (most within 3 months) and MRSA SSTI hospitalization rates decreased over time (e.g., 1.72 per 1000 in 2016 to 1.32 per 1000 by 2019 in the US). (linz2023clinicalimpactof pages 1-2)

1.2 Malassezia (Pityrosporum) folliculitis

Trigger/initiating event. Malassezia are lipid-dependent commensal yeasts; disease reflects follicular overgrowth in sebum-rich areas promoted by humidity, occlusion, antibiotic exposure, and immunosuppression. (chalupczak2025malasseziafolliculitisan pages 1-2)

Dysregulated pathways: keratinocyte innate immunity + type 17 axis. A mechanistic review notes that Malassezia can induce keratinocytes to produce cytokines including IL‑1α, IL‑6, IL‑8, IL‑12, TNF‑α, and also IL‑4 and IL‑10 “via Toll-like receptor 2 (TLR2),” with complement activation via classical and alternative pathways. (chalupczak2025malasseziafolliculitisan pages 1-2) In addition, murine epicutaneous infection models report Malassezia “selectively induce interleukin-17 (IL-17) and related cytokines,” and cell profiling found “neutrophils, and Langerhans cells were found to express the highest levels of IL-23 transcripts,” supporting an IL‑23/IL‑17 axis with innate myeloid/antigen-presenting cell involvement. (martinezortega2024malasseziafolliculitispathogenesis pages 4-5)

Cellular processes affected. Follicular plugging/occlusion and folliculocentric inflammation are emphasized, consistent with a sequence of (i) follicular environment changes (lipids, humidity, occlusion) → (ii) yeast proliferation in the follicle → (iii) keratinocyte PRR activation and complement engagement → (iv) recruitment of inflammatory leukocytes (including neutrophils in type-17–skewed responses) → pustule formation. (chalupczak2025malasseziafolliculitisan pages 1-2, martinezortega2024malasseziafolliculitispathogenesis pages 4-5)

Quantitative data (recent cohorts/reviews). A 2023 systematic review aggregating 1,238 immunocompetent patients found mean age ~24.3 years, male predominance ~64%, common sites chest (~70%) and back/shoulders (~69%), and pruritus in ~71.7%. (green2023clinicalcharacteristicsand pages 2-4) Diagnostic performance and treatment outcomes include KOH smear sensitivity/specificity “up to 84.6% and 100%,” and high response rates to antifungals (oral ~92% improvement; topical ~81.6%). (green2023clinicalcharacteristicsand pages 1-2) Another review reports Wood’s lamp “low sensitivity (65.3%) for MF diagnosis.” (martinezortega2024malasseziafolliculitispathogenesis pages 4-5)

1.3 Eosinophilic pustular folliculitis (EPF; Ofuji disease)

Core lesion biology. EPF is characterized histologically by eosinophil-rich folliculocentric inflammation and microabscess formation. In a 10-patient clinicopathologic series (2023), histopathology included “intraepithelial spongiform oedema with eosinophil migration into hair follicles,” and “eosinophilic and neutrophilic abscesses in hair follicles,” with eosinophilic microabscesses around appendages and perivascular regions. (li2023clinicalandpathological pages 1-2)

Mechanistic model (cell trafficking and follicular destruction). The same study frames EPF as eosinophil recruitment into sebaceous follicles, mixing with neutrophils and promoting “fragmentation of follicular epithelium” with “small abscesses” and mucinosis-like changes. (li2023clinicalandpathological pages 5-6)

Type 2–skewed pathways (current literature). A recent review-level summary highlights prostaglandin D2 (PGD2) chemotaxis via CRTH2 (PTGDR2) implicating recruitment of Th2 cells, eosinophils, and basophils. (li2025successfultreatmentof pages 8-8) Additional mechanistic framing supports Th2 cytokines (IL‑4/IL‑5/IL‑13) and eosinophil biology in EPF. (danielson2025dermatologiclesionswith pages 3-4)

Quantitative data (10-case series + image table). In Li et al. 2023, EPF cases spanned ages 22–45 with 5 male/5 female, and pruritus occurred in 7/10. Peripheral eosinophil counts were reported per case (one normal; others elevated). (li2023clinicalandpathological pages 1-2) Table 1 visually summarizes these patient characteristics and eosinophil counts. (li2023clinicalandpathological media 4cdf4055)

1.4 Folliculitis decalvans (FD)

Core lesion biology. FD is a chronic neutrophilic folliculitis of the scalp that leads to scarring alopecia. It is often linked clinically to S. aureus, but emerging data support broader dysbiosis/microbiome heterogeneity.

Microbiome + immune dysfunction concept. A 2023 cross-sectional study using trichoscopy-guided biopsies is explicitly framed as showing a “heterogeneous microbiological signature and impaired immunological response,” and targeted staphylococcal virulence markers (e.g., pvl, mecA) were assessed. (morenoarrones2023folliculitisdecalvanshas pages 2-3)

Immune privilege collapse and lichenoid phase hypothesis. The same FD study proposes that microbiota perturbation could cause “a collapse of follicular immune privilege,” exposing follicular antigens and “triggering a lichenoid response against the hair follicle.” (morenoarrones2023folliculitisdecalvanshas pages 8-8)

Drug-induced implementation: EGFR inhibitor–associated FD. In oncology, EGFR inhibitors can precipitate FD-like scarring folliculitis; the mechanistic framing is that EGFR inhibitor adverse reactions arise from “disturbances in keratinocyte differentiation, cytokine secretion, and neutrophil chemotaxis,” producing sterile folliculitis with frequent secondary bacterial superinfection; S. aureus is “frequently cultured” and its superantigens “may contribute to pathogenesis.” (nowaczyk2023egfrinhibitorinducedfolliculitis pages 1-3, nowaczyk2023egfrinhibitorinducedfolliculitis pages 3-5)

2) Key molecular players (genes/proteins), chemical entities, cell types, and anatomical locations

2.1 Genes/proteins and pathways (HGNC-style names where applicable)

Innate sensors / signaling - TLR2: implicated in Malassezia-induced keratinocyte cytokine responses and in bacterial skin infection PRR recognition. (chalupczak2025malasseziafolliculitisan pages 1-2, linz2023clinicalimpactof pages 10-11) - NOD2: PRR implicated in bacterial skin infection models; loss increases bacterial burden/NF‑κB activity. (linz2023clinicalimpactof pages 10-11) - MYD88 and IL36R (IL1RL2 / IL‑36 receptor axis): cited as mediating “Malassezia-induced IL-17-dependent skin inflammation.” (martinezortega2024malasseziafolliculitispathogenesis pages 6-7)

Cytokines/chemokines (examples strongly represented in evidence) - IL1A, IL6, CXCL8 (IL-8), IL12, TNF: induced in keratinocytes by Malassezia via TLR2 (as described in review evidence). (chalupczak2025malasseziafolliculitisan pages 1-2) - IL23 (IL23A as a component of IL‑23): IL‑23 transcripts highest in neutrophils/Langerhans cells in Malassezia skin model. (martinezortega2024malasseziafolliculitispathogenesis pages 4-5) - IL17 axis (e.g., IL17A/IL17F conceptually): Malassezia “selectively induce IL‑17 and related cytokines.” (martinezortega2024malasseziafolliculitispathogenesis pages 4-5) - IL33: promotes NETs via NADPH oxidase in S. aureus skin infection context. (linz2023clinicalimpactof pages 10-11)

Host targets / epithelial injury - ADAM10: Hla binds ADAM10 and disrupts epithelial adhesion (E‑cadherin cleavage). (linz2023clinicalimpactof pages 5-7) - PTGS2 (COX2) and IL8: protein A can induce keratinocyte proinflammatory genes including COX2 and IL8. (linz2023clinicalimpactof pages 10-11)

Microbial virulence factors - PVL (lukS-PV/lukF-PV; toxin concept): associated with furunculosis; PVL positivity 40–90% in furunculosis. (linz2023clinicalimpactof pages 3-5) - Hla (alpha-hemolysin): keratinocyte necrosis and epithelial disruption. (linz2023clinicalimpactof pages 10-11, linz2023clinicalimpactof pages 5-7) - Protein A (spa; virulence concept): immune evasion and keratinocyte activation. (linz2023clinicalimpactof pages 10-11) - Coagulase (coa) / vWbp: implicated in abscess formation. (linz2023clinicalimpactof pages 10-11)

2.2 Chemical entities (CHEBI-style)

Prostaglandin D2 (PGD2): chemotaxis via CRTH2 described for EPF. (li2025successfultreatmentof pages 8-8)
Indomethacin: commonly effective/first-line in EPF with rapid responses in case series experience. (li2023clinicalandpathological pages 5-6)
Itraconazole, ketoconazole: key antifungals for Malassezia folliculitis; strong response rates across cohorts. (martinezortega2024malasseziafolliculitispathogenesis pages 1-3, green2023clinicalcharacteristicsand pages 2-4)
Tetracyclines/doxycycline: used for FD (including EGFR inhibitor–associated FD) with both antibacterial and anti-inflammatory roles; typical durations 4–16 weeks cited. (nowaczyk2023egfrinhibitorinducedfolliculitis pages 5-5)

2.3 Cell types (CL-style)

Keratinocytes: central epithelial responders producing cytokines after microbial sensing. (chalupczak2025malasseziafolliculitisan pages 1-2, linz2023clinicalimpactof pages 10-11)
Neutrophils: dominant effector cells in bacterial folliculitis/furunculosis and FD; implicated in IL‑23 transcripts in Malassezia model; drive pustules and scarring follicular destruction in FD. (martinezortega2024malasseziafolliculitispathogenesis pages 4-5, nowaczyk2023egfrinhibitorinducedfolliculitis pages 3-5, linz2023clinicalimpactof pages 10-11)
Eosinophils: dominant effector cells in EPF; migrate into follicles and form microabscesses. (li2023clinicalandpathological pages 1-2)
Langerhans cells: implicated as IL‑23 transcript-high cells in Malassezia model; also recognize S. aureus via langerin in SSTI review. (martinezortega2024malasseziafolliculitispathogenesis pages 4-5, linz2023clinicalimpactof pages 10-11)
Plasma cells: part of FD infiltrate in EGFR inhibitor-associated FD histopathology (“rich in neutrophils and plasma cells”). (nowaczyk2023egfrinhibitorinducedfolliculitis pages 3-5)

2.4 Anatomical locations (UBERON-style)

Pilosebaceous unit / hair follicle: primary inflammatory compartment across folliculitis entities. (li2023clinicalandpathological pages 1-2, nowaczyk2023egfrinhibitorinducedfolliculitis pages 3-5)
Sebaceous-rich truncal skin (chest/back/shoulders): common distribution for Malassezia folliculitis. (green2023clinicalcharacteristicsand pages 2-4)
Scalp hair follicles: primary site for FD and EGFR inhibitor-associated FD. (morenoarrones2023folliculitisdecalvanshas pages 2-3, nowaczyk2023egfrinhibitorinducedfolliculitis pages 3-5)

3) Biological processes disrupted (GO-oriented)

Representative processes, with evidence linkage: - Innate immune response / PRR signaling (TLR2, NOD2) (chalupczak2025malasseziafolliculitisan pages 1-2, linz2023clinicalimpactof pages 10-11) - Cytokine-mediated signaling pathways (IL‑1/IL‑6/IL‑8/TNF; IL‑23/IL‑17) (chalupczak2025malasseziafolliculitisan pages 1-2, martinezortega2024malasseziafolliculitispathogenesis pages 4-5, linz2023clinicalimpactof pages 10-11) - Granulocyte chemotaxis and activation: neutrophil chemotaxis in FD (drug-induced model) and bacterial folliculitis; eosinophil migration in EPF. (li2023clinicalandpathological pages 1-2, nowaczyk2023egfrinhibitorinducedfolliculitis pages 1-3, linz2023clinicalimpactof pages 10-11) - Complement activation in Malassezia folliculitis. (chalupczak2025malasseziafolliculitisan pages 1-2) - Epithelial cell death and barrier disruption (keratinocyte necrosis; epithelial adhesion disruption). (linz2023clinicalimpactof pages 5-7)

4) Cellular components (subcellular/compartment focus)

Follicular lumen and follicular epithelium: site of Malassezia overgrowth, follicular plugging, and inflammatory infiltration. (martinezortega2024malasseziafolliculitispathogenesis pages 4-5, li2023clinicalandpathological pages 1-2)
Perifollicular dermis / perivascular spaces: common inflammatory distribution in EPF and FD, including mixed infiltrates and microabscesses. (morenoarrones2023folliculitisdecalvanshas pages 8-8, li2023clinicalandpathological pages 1-2)

5) Disease progression: sequence of events (by subtype)

5.1 Malassezia folliculitis progression (conceptual)

Environmental/host predisposition (humidity, occlusion, antibiotic exposure) promotes yeast overgrowth in sebum-rich follicles. (chalupczak2025malasseziafolliculitisan pages 1-2)
Keratinocytes sense Malassezia via TLR2 and produce inflammatory mediators (IL‑1α, IL‑6, IL‑8, IL‑12, TNF‑α), with complement activation. (chalupczak2025malasseziafolliculitisan pages 1-2)
Type-17–linked inflammation emerges; Malassezia induces IL‑17, with IL‑23 transcripts in neutrophils/Langerhans cells in model systems. (martinezortega2024malasseziafolliculitispathogenesis pages 4-5)
Clinical manifestation: monomorphic pruritic follicular papules/pustules and a chronic-relapsing course. (chalupczak2025malasseziafolliculitisan pages 1-2)

5.2 EPF progression (clinicopathologic)

Triggering antigenic stimuli (often unclear) with preferential involvement of sebaceous areas. (li2023clinicalandpathological pages 2-5)
Eosinophil recruitment into follicles → spongiosis and eosinophil migration into follicular epithelium. (li2023clinicalandpathological pages 1-2)
Formation of eosinophilic (and often mixed eosinophilic/neutrophilic) follicular abscesses with follicular destruction. (li2023clinicalandpathological pages 2-5)
Clinical plaques/pustules; typically heal with post-inflammatory hyperpigmentation without scarring in the case series experience. (li2023clinicalandpathological pages 5-6)

5.3 FD progression (conceptual + drug-induced model)

Microbiome perturbation/dysbiosis may collapse follicular immune privilege → antigen exposure → lichenoid response. (morenoarrones2023folliculitisdecalvanshas pages 8-8)
Neutrophilic perifollicular inflammation leads to follicular destruction and permanent scarring alopecia. (nowaczyk2023egfrinhibitorinducedfolliculitis pages 3-5)
In EGFR inhibitor-associated FD: keratinocyte differentiation defects and neutrophil chemotaxis contribute to sterile folliculitis with frequent S. aureus superinfection, amplifying inflammation. (nowaczyk2023egfrinhibitorinducedfolliculitis pages 1-3, nowaczyk2023egfrinhibitorinducedfolliculitis pages 3-5)

6) Phenotypic manifestations (HP-oriented)

Follicular papules/pustules (common across subtypes) (chalupczak2025malasseziafolliculitisan pages 1-2, li2023clinicalandpathological pages 1-2)
Pruritus (notable in Malassezia folliculitis; common in EPF) (green2023clinicalcharacteristicsand pages 2-4, li2023clinicalandpathological pages 1-2)
Scarring alopecia (FD; deep folliculitis) (nowaczyk2023egfrinhibitorinducedfolliculitis pages 3-5, linz2023clinicalimpactof pages 3-5)

7) Recent developments and latest research emphasis (prioritizing 2023–2024)

7.1 2023–2024 highlights

FD microbiome + immune response framing (2023): FD characterized by “heterogeneous microbiological signature and impaired immunological response,” with a mechanistic hypothesis of immune privilege collapse and lichenoid response. (morenoarrones2023folliculitisdecalvanshas pages 2-3, morenoarrones2023folliculitisdecalvanshas pages 8-8)
Malassezia folliculitis immunology axis (2024): epicutaneous model evidence supports Malassezia-driven IL‑17 responses and IL‑23 production by myeloid/Langerhans subsets, and provides diagnostic quantification (Wood’s lamp sensitivity 65.3%). (martinezortega2024malasseziafolliculitispathogenesis pages 4-5)
EPF clinicopathology (2023): detailed histopathology and patient-level eosinophil counts in a 10-case series provide a contemporary phenotype/biology anchor for EPF. (li2023clinicalandpathological pages 1-2, li2023clinicalandpathological media 4cdf4055)
EGFR inhibitor-associated FD (2023): mechanistic linkage to keratinocyte differentiation/cytokine secretion/neutrophil chemotaxis, with practical prevention/management guidance (pre-emptive tetracyclines/topical steroids). (nowaczyk2023egfrinhibitorinducedfolliculitis pages 1-3, nowaczyk2023egfrinhibitorinducedfolliculitis pages 5-6)

8) Current applications and real-world implementations

8.1 Diagnostic implementation

Malassezia folliculitis: KOH smear and histopathology are widely used. In the 2023 systematic review, KOH sensitivity/specificity reported up to 84.6%/100%. (green2023clinicalcharacteristicsand pages 1-2) Wood’s lamp has 65.3% sensitivity in one report. (martinezortega2024malasseziafolliculitispathogenesis pages 4-5) Misdiagnosis is common: ~40.5% had prior unsuccessful treatments (often acne-directed). (green2023clinicalcharacteristicsand pages 2-4)
EPF: biopsy is central; Table 1 in Li et al. 2023 summarizes clinical features and eosinophil counts for 10 cases. (li2023clinicalandpathological media 4cdf4055)
FD: trichoscopy-guided biopsy and microbiologic evaluation; EGFR inhibitor-associated FD emphasizes trichoscopy as a key noninvasive diagnostic tool and highlights the need to identify/treat superinfection to prevent severe complications in immunocompromised patients. (nowaczyk2023egfrinhibitorinducedfolliculitis pages 3-5)

8.2 Therapeutic implementation (mechanism-aligned)

Malassezia folliculitis: antifungals are highly effective; 2023 aggregated data indicate oral antifungals ~92% success and topical ~81.6%. (green2023clinicalcharacteristicsand pages 1-2)
EPF: indomethacin is commonly effective and described as a preferred/first-line option; in one cohort segment, responses are often within weeks. (li2023clinicalandpathological pages 5-6)
FD (including EGFR inhibitor-associated): systemic tetracyclines and topical steroids/antibiotics are used; tetracyclines “should be continued for 4 up to 16 weeks,” then tapered to anti-inflammatory doses for maintenance. (nowaczyk2023egfrinhibitorinducedfolliculitis pages 5-5)

9) Evidence items with identifiers (PMIDs preferred)

PMIDs were not available in the extracted evidence snippets during this tool run; therefore, below are DOI-based evidence anchors (each is a peer-reviewed article unless otherwise noted): - Linz MS et al. Antibiotics (Mar 2023). DOI: 10.3390/antibiotics12030557. (linz2023clinicalimpactof pages 1-2) - Moreno-Arrones OM et al. Dermatology (Jan 2023). DOI: 10.1159/000529301. (morenoarrones2023folliculitisdecalvanshas pages 2-3) - Nowaczyk J et al. Anti-Cancer Drugs (Jan 2023). DOI: 10.1097/CAD.0000000000001494. (nowaczyk2023egfrinhibitorinducedfolliculitis pages 1-3) - Green M et al. Archives of Dermatological Research (Dec 2023). DOI: 10.1007/s00403-022-02506-0. (green2023clinicalcharacteristicsand pages 2-4) - Li Y et al. Clinical, Cosmetic and Investigational Dermatology (Sep 2023). DOI: 10.2147/CCID.S427718. (li2023clinicalandpathological pages 1-2) - Martínez-Ortega JI et al. Cureus (Nov 2024). DOI: 10.7759/cureus.73429. (martinezortega2024malasseziafolliculitispathogenesis pages 4-5)

10) Key direct-quote excerpts supporting major mechanistic claims

Malassezia folliculitis model evidence: Malassezia spp. “selectively induce interleukin-17 (IL-17) and related cytokines,” and “neutrophils, and Langerhans cells were found to express the highest levels of IL-23 transcripts.” (martinezortega2024malasseziafolliculitispathogenesis pages 4-5)
FD immune-privilege hypothesis: microbiota perturbation may cause “a collapse of follicular immune privilege,” exposing follicular antigens and “triggering a lichenoid response against the hair follicle.” (morenoarrones2023folliculitisdecalvanshas pages 8-8)
EGFR inhibitor-associated FD mechanism: adverse reactions originate from “disturbances in keratinocyte differentiation, cytokine secretion, and neutrophil chemotaxis.” (nowaczyk2023egfrinhibitorinducedfolliculitis pages 1-3)
Furunculosis PVL association: PVL reported positive in 40–90% of furunculosis. (linz2023clinicalimpactof pages 3-5)

Conclusion

Folliculitis comprises mechanistically distinct folliculocentric inflammatory disorders unified by follicular barrier disruption and innate immune activation. Recent 2023–2024 literature emphasizes (i) microbiome heterogeneity and impaired immunity in folliculitis decalvans with a proposed immune-privilege collapse/lichenoid phase; (ii) Malassezia-driven keratinocyte innate activation coupled to an IL‑23/IL‑17 (type-17) axis involving neutrophils and Langerhans cells; and (iii) eosinophilic pustular folliculitis as an eosinophil-dominant, often type-2–skewed disorder with characteristic follicular eosinophilic microabscesses and clinically meaningful response to indomethacin. (morenoarrones2023folliculitisdecalvanshas pages 2-3, martinezortega2024malasseziafolliculitispathogenesis pages 4-5, li2023clinicalandpathological pages 1-2, nowaczyk2023egfrinhibitorinducedfolliculitis pages 3-5)

References

(martinezortega2024malasseziafolliculitispathogenesis pages 4-5): Jesús Iván Martínez-Ortega, Jacqueline E Mut Quej, and Samantha Franco González. Malassezia folliculitis: pathogenesis and diagnostic challenges. Cureus, Nov 2024. URL: https://doi.org/10.7759/cureus.73429, doi:10.7759/cureus.73429. This article has 8 citations.
(morenoarrones2023folliculitisdecalvanshas pages 8-8): Oscar M. Moreno-Arrones, Carlota Garcia-Hoz, Rosa del Campo, Garbiñe Roy, David Saceda-Corralo, Juan Jimenez-Cauhe, Manuel Ponce-Alonso, Sergio Serrano-Villar, Pedro Jaen, John Paoli, and Sergio Vano-Galvan. Folliculitis decalvans has a heterogeneous microbiological signature and impaired immunological response. Dermatology, 239:454-461, Jan 2023. URL: https://doi.org/10.1159/000529301, doi:10.1159/000529301. This article has 14 citations and is from a peer-reviewed journal.
(li2023clinicalandpathological pages 5-6): Yuan Li, Gaihe Chen, Xin Zhou, Xiaole Zheng, Ming Zhang, Xiaojuan Yao, Jiejie Lu, and Xiaohuan Hu. Clinical and pathological analysis of 10 cases of eosinophilic pustular folliculitis. Clinical, Cosmetic and Investigational Dermatology, 16:2467-2472, Sep 2023. URL: https://doi.org/10.2147/ccid.s427718, doi:10.2147/ccid.s427718. This article has 4 citations and is from a peer-reviewed journal.
(nowaczyk2023egfrinhibitorinducedfolliculitis pages 3-5): Joanna Nowaczyk, Kamil Fret, Grazyna Kaminska-Winciorek, Lidia Rudnicka, and Joanna Czuwara. Egfr inhibitor-induced folliculitis decalvans: a case series and management guidelines. Anti-Cancer Drugs, 34:942-948, Jan 2023. URL: https://doi.org/10.1097/cad.0000000000001494, doi:10.1097/cad.0000000000001494. This article has 9 citations and is from a peer-reviewed journal.
(linz2023clinicalimpactof pages 3-5): Matthew S. Linz, Arun Mattappallil, Diana Finkel, and Dane Parker. Clinical impact of staphylococcus aureus skin and soft tissue infections. Antibiotics, 12:557, Mar 2023. URL: https://doi.org/10.3390/antibiotics12030557, doi:10.3390/antibiotics12030557. This article has 279 citations.
(linz2023clinicalimpactof pages 10-11): Matthew S. Linz, Arun Mattappallil, Diana Finkel, and Dane Parker. Clinical impact of staphylococcus aureus skin and soft tissue infections. Antibiotics, 12:557, Mar 2023. URL: https://doi.org/10.3390/antibiotics12030557, doi:10.3390/antibiotics12030557. This article has 279 citations.
(linz2023clinicalimpactof pages 5-7): Matthew S. Linz, Arun Mattappallil, Diana Finkel, and Dane Parker. Clinical impact of staphylococcus aureus skin and soft tissue infections. Antibiotics, 12:557, Mar 2023. URL: https://doi.org/10.3390/antibiotics12030557, doi:10.3390/antibiotics12030557. This article has 279 citations.
(linz2023clinicalimpactof pages 1-2): Matthew S. Linz, Arun Mattappallil, Diana Finkel, and Dane Parker. Clinical impact of staphylococcus aureus skin and soft tissue infections. Antibiotics, 12:557, Mar 2023. URL: https://doi.org/10.3390/antibiotics12030557, doi:10.3390/antibiotics12030557. This article has 279 citations.
(chalupczak2025malasseziafolliculitisan pages 1-2): Natalia V. Chalupczak and Shari R. Lipner. Malassezia folliculitis: an underdiagnosed mimicker of acneiform eruptions. Journal of Fungi, 11:662, Sep 2025. URL: https://doi.org/10.3390/jof11090662, doi:10.3390/jof11090662. This article has 2 citations.
(green2023clinicalcharacteristicsand pages 2-4): Maxwell Green, Aileen M. Feschuk, Nadia Kashetsky, and Howard I. Maibach. Clinical characteristics and treatment outcomes of pityrosporum folliculitis in immunocompetent patients. Archives of Dermatological Research, 315:1-13, Dec 2023. URL: https://doi.org/10.1007/s00403-022-02506-0, doi:10.1007/s00403-022-02506-0. This article has 13 citations and is from a peer-reviewed journal.
(green2023clinicalcharacteristicsand pages 1-2): Maxwell Green, Aileen M. Feschuk, Nadia Kashetsky, and Howard I. Maibach. Clinical characteristics and treatment outcomes of pityrosporum folliculitis in immunocompetent patients. Archives of Dermatological Research, 315:1-13, Dec 2023. URL: https://doi.org/10.1007/s00403-022-02506-0, doi:10.1007/s00403-022-02506-0. This article has 13 citations and is from a peer-reviewed journal.
(li2023clinicalandpathological pages 1-2): Yuan Li, Gaihe Chen, Xin Zhou, Xiaole Zheng, Ming Zhang, Xiaojuan Yao, Jiejie Lu, and Xiaohuan Hu. Clinical and pathological analysis of 10 cases of eosinophilic pustular folliculitis. Clinical, Cosmetic and Investigational Dermatology, 16:2467-2472, Sep 2023. URL: https://doi.org/10.2147/ccid.s427718, doi:10.2147/ccid.s427718. This article has 4 citations and is from a peer-reviewed journal.
(li2025successfultreatmentof pages 8-8): Wanni Li, Xiaohuan Hu, Yuan Li, and Gaihe Chen. Successful treatment of eosinophilic pustular folliculitis with secondary follicular mucin deposition using indomethacin: an atypical case and literature review. Clinical, Cosmetic and Investigational Dermatology, 18:1063-1070, May 2025. URL: https://doi.org/10.2147/ccid.s520968, doi:10.2147/ccid.s520968. This article has 0 citations and is from a peer-reviewed journal.
(danielson2025dermatologiclesionswith pages 3-4): David T. Danielson, Ian Lagerstrom, Zachary Wary, Aaron Auerbach, and David S. Cassarino. Dermatologic lesions with eosinophilia in the head and neck. Head and Neck Pathology, Feb 2025. URL: https://doi.org/10.1007/s12105-025-01757-3, doi:10.1007/s12105-025-01757-3. This article has 1 citations and is from a peer-reviewed journal.
(li2023clinicalandpathological media 4cdf4055): Yuan Li, Gaihe Chen, Xin Zhou, Xiaole Zheng, Ming Zhang, Xiaojuan Yao, Jiejie Lu, and Xiaohuan Hu. Clinical and pathological analysis of 10 cases of eosinophilic pustular folliculitis. Clinical, Cosmetic and Investigational Dermatology, 16:2467-2472, Sep 2023. URL: https://doi.org/10.2147/ccid.s427718, doi:10.2147/ccid.s427718. This article has 4 citations and is from a peer-reviewed journal.
(morenoarrones2023folliculitisdecalvanshas pages 2-3): Oscar M. Moreno-Arrones, Carlota Garcia-Hoz, Rosa del Campo, Garbiñe Roy, David Saceda-Corralo, Juan Jimenez-Cauhe, Manuel Ponce-Alonso, Sergio Serrano-Villar, Pedro Jaen, John Paoli, and Sergio Vano-Galvan. Folliculitis decalvans has a heterogeneous microbiological signature and impaired immunological response. Dermatology, 239:454-461, Jan 2023. URL: https://doi.org/10.1159/000529301, doi:10.1159/000529301. This article has 14 citations and is from a peer-reviewed journal.
(nowaczyk2023egfrinhibitorinducedfolliculitis pages 1-3): Joanna Nowaczyk, Kamil Fret, Grazyna Kaminska-Winciorek, Lidia Rudnicka, and Joanna Czuwara. Egfr inhibitor-induced folliculitis decalvans: a case series and management guidelines. Anti-Cancer Drugs, 34:942-948, Jan 2023. URL: https://doi.org/10.1097/cad.0000000000001494, doi:10.1097/cad.0000000000001494. This article has 9 citations and is from a peer-reviewed journal.
(martinezortega2024malasseziafolliculitispathogenesis pages 6-7): Jesús Iván Martínez-Ortega, Jacqueline E Mut Quej, and Samantha Franco González. Malassezia folliculitis: pathogenesis and diagnostic challenges. Cureus, Nov 2024. URL: https://doi.org/10.7759/cureus.73429, doi:10.7759/cureus.73429. This article has 8 citations.
(martinezortega2024malasseziafolliculitispathogenesis pages 1-3): Jesús Iván Martínez-Ortega, Jacqueline E Mut Quej, and Samantha Franco González. Malassezia folliculitis: pathogenesis and diagnostic challenges. Cureus, Nov 2024. URL: https://doi.org/10.7759/cureus.73429, doi:10.7759/cureus.73429. This article has 8 citations.
(nowaczyk2023egfrinhibitorinducedfolliculitis pages 5-5): Joanna Nowaczyk, Kamil Fret, Grazyna Kaminska-Winciorek, Lidia Rudnicka, and Joanna Czuwara. Egfr inhibitor-induced folliculitis decalvans: a case series and management guidelines. Anti-Cancer Drugs, 34:942-948, Jan 2023. URL: https://doi.org/10.1097/cad.0000000000001494, doi:10.1097/cad.0000000000001494. This article has 9 citations and is from a peer-reviewed journal.
(li2023clinicalandpathological pages 2-5): Yuan Li, Gaihe Chen, Xin Zhou, Xiaole Zheng, Ming Zhang, Xiaojuan Yao, Jiejie Lu, and Xiaohuan Hu. Clinical and pathological analysis of 10 cases of eosinophilic pustular folliculitis. Clinical, Cosmetic and Investigational Dermatology, 16:2467-2472, Sep 2023. URL: https://doi.org/10.2147/ccid.s427718, doi:10.2147/ccid.s427718. This article has 4 citations and is from a peer-reviewed journal.
(nowaczyk2023egfrinhibitorinducedfolliculitis pages 5-6): Joanna Nowaczyk, Kamil Fret, Grazyna Kaminska-Winciorek, Lidia Rudnicka, and Joanna Czuwara. Egfr inhibitor-induced folliculitis decalvans: a case series and management guidelines. Anti-Cancer Drugs, 34:942-948, Jan 2023. URL: https://doi.org/10.1097/cad.0000000000001494, doi:10.1097/cad.0000000000001494. This article has 9 citations and is from a peer-reviewed journal.

{ }

Source YAML

click to show

name: Folliculitis
creation_date: '2026-03-01T22:48:38Z'
updated_date: '2026-03-02T19:29:56Z'
category: Complex
description: >-
  Folliculitis is inflammation of hair follicles with infectious and noninfectious
  etiologies, typically presenting with follicular papules, papulopustules, and
  pruritus.
disease_term:
  preferred_term: folliculitis
  term:
    id: MONDO:0006552
    label: folliculitis
classifications:
  harrisons_chapter:
  - classification_value: skin disorder
    evidence:
    - reference: PMID:22639852
      reference_title: "First step in the differential diagnosis of folliculitis: cytology."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Folliculitis is a superficial inflammation of the hair follicles, and can be observed in individuals of any age or race."
      explanation: Supports classification as a skin disorder affecting hair follicles and appendages.
parents:
- dermatitis
- disorder of pilosebaceous unit
has_subtypes:
- name: Staphylococcal folliculitis
  classification: etiologic
  description: Superficial bacterial folliculitis in which Staphylococcus aureus is the predominant causative organism.
  evidence:
  - reference: PMID:22639852
    reference_title: "First step in the differential diagnosis of folliculitis: cytology."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "There are various infectious and non-infectious causes of folliculitis, and the most common causative agent is Staphylococcus aureus."
    explanation: Supports staphylococcal folliculitis as the most common etiologic subtype.
  - reference: PMID:15482221
    reference_title: "Treatment of staphylococcal scalded skin syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "S. aureus is one of the most common causes of skin infection, giving rise to folliculitis, furunculosis, carbuncles, ecthyma, impetigo, cellulitis and abscesses."
    explanation: Independent review evidence supports staphylococcal folliculitis within the common S. aureus skin-infection spectrum.
- name: Pseudomonas hot-tub folliculitis
  classification: exposure_associated
  description: Water-exposure-associated folliculitis caused by Pseudomonas aeruginosa after contaminated hot-tub or spa use.
  evidence:
  - reference: PMID:6402527
    reference_title: "Hot tub dermatitis: a familial outbreak of Pseudomonas folliculitis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Pseudomonas folliculitis resulting from the use of spa pools, whirlpools, and hot tubs is a newly described disease that typically develops 8 to 48 hours after exposure in a contaminated facility."
    explanation: Defines a distinct exposure-associated pseudomonal subtype.
- name: Malassezia folliculitis
  classification: etiologic
  description: Lipophilic yeast-associated folliculitis presenting with pruritic papules and pustules.
  evidence:
  - reference: PMID:36912427
    reference_title: "Position statement: Recommendations on the diagnosis and treatment of Malassezia folliculitis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Malassezia folliculitis appears when the benign colonization of the hair follicles, by the Malassezia yeasts, becomes symptomatic with pruritic papules and pustules."
    explanation: Supports Malassezia as a clinically distinct etiologic subtype.
- name: Demodex-associated folliculitis
  classification: etiologic
  description: Folliculitis associated with Demodex mite colonization and increased histologic inflammation.
  evidence:
  - reference: PMID:8989930
    reference_title: "Demodex-associated folliculitis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Demodex mites were found in 42% of follicles with inflammation, but in just 10% of the follicles without inflammation."
    explanation: Supports a Demodex-associated folliculitis subtype with inflammatory enrichment.
- name: Gram-negative folliculitis
  classification: treatment_associated
  description: Folliculitis caused by gram-negative rods, commonly emerging after prolonged broad-spectrum antibiotic therapy in acne/rosacea contexts.
  evidence:
  - reference: PMID:10321942
    reference_title: "Bacteriologic and immunologic aspects of gram-negative folliculitis: a study of 46 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Gram-negative folliculitis is an infection with gram-negative rods that most often occurs as a complication of prolonged broad-spectrum antibiotic therapy in patients suffering from acne and rosacea."
    explanation: Supports gram-negative folliculitis as a treatment-associated subtype.
- name: HIV-associated eosinophilic folliculitis
  classification: immunologic
  description: Culture-negative chronic pruritic folliculitis with eosinophilic inflammatory pattern in advanced HIV.
  evidence:
  - reference: PMID:1671328
    reference_title: "Human immunodeficiency virus-associated eosinophilic folliculitis. A unique dermatosis associated with advanced human immunodeficiency virus infection."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These observations demonstrate that HIV-associated eosinophilic folliculitis is a unique HIV-related cutaneous disorder that is characterized by a culture-negative, chronic, pruritic folliculitis and a characteristic histopathologic picture."
    explanation: Supports a distinct HIV-associated eosinophilic subtype.
- name: Folliculitis decalvans
  classification: clinical_phenotype
  description: Chronic neutrophilic scarring folliculitis of the scalp with recurrent inflammation and progressive alopecia.
  evidence:
  - reference: PMID:36716709
    reference_title: "Folliculitis Decalvans Has a Heterogeneous Microbiological Signature and Impaired Immunological Response."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "BACKGROUND: Folliculitis decalvans (FD) is a rare primary neutrophilic scarring alopecia whose etiology has not been completely elucidated yet."
    explanation: Supports folliculitis decalvans as a clinically distinct scarring subtype.
  - reference: PMID:18715292
    reference_title: "Folliculitis decalvans."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Folliculitis decalvans is classified as primary neutrophilic cicatricial alopecia and predominantly occurs in middle-aged adults."
    explanation: Adds independent subtype-level characterization of FD as primary neutrophilic cicatricial alopecia.
- name: EGFR inhibitor-induced folliculitis
  classification: treatment_induced
  description: Folliculitis developing during anti-EGFR therapy, including chronic and scarring inflammatory forms in susceptible patients.
  evidence:
  - reference: clinicaltrials:NCT06818058
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A Phase II, multicentric, randomized, double-blind, placebo-controlled, parallel- group trial to confirm the good safaty profile and to explore the preventive effect of topically applied TAR-0520 gel on folliculitis developed in metastatic colorectal cancer (mCRC) patients treated with monoclonal anti-EGFR antibodies."
    explanation: Supports anti-EGFR-therapy-associated folliculitis as a clinically recognized treatment-induced subtype.
infectious_agent:
- name: Staphylococcus aureus
  infectious_agent_term:
    preferred_term: Staphylococcus aureus
    term:
      id: NCBITaxon:1280
      label: Staphylococcus aureus
  description: Most common microbial cause of infectious folliculitis.
  evidence:
  - reference: PMID:22639852
    reference_title: "First step in the differential diagnosis of folliculitis: cytology."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "There are various infectious and non-infectious causes of folliculitis, and the most common causative agent is Staphylococcus aureus."
    explanation: The review identifies S. aureus as the most common causative pathogen.
  - reference: PMID:15482221
    reference_title: "Treatment of staphylococcal scalded skin syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "S. aureus is one of the most common causes of skin infection, giving rise to folliculitis, furunculosis, carbuncles, ecthyma, impetigo, cellulitis and abscesses."
    explanation: Additional clinical review evidence supports S. aureus as a major folliculitis pathogen.
- name: Pseudomonas aeruginosa
  infectious_agent_term:
    preferred_term: Pseudomonas aeruginosa
    term:
      id: NCBITaxon:287
      label: Pseudomonas aeruginosa
  description: Water-associated pathogen causing hot-tub folliculitis outbreaks.
  evidence:
  - reference: PMID:6402527
    reference_title: "Hot tub dermatitis: a familial outbreak of Pseudomonas folliculitis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A family of three and a neighbor developed Pseudomonas folliculitis after using a home hot tub from which P. aeruginosa was cultured."
    explanation: Human outbreak evidence supports P. aeruginosa as an etiologic agent in exposure-associated folliculitis.
  - reference: PMID:3955486
    reference_title: "Nosocomial outbreak of Pseudomonas aeruginosa folliculitis associated with a physiotherapy pool."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Outbreaks of community-acquired Pseudomonas aeruginosa folliculitis have recently been described in association with health spa whirlpools."
    explanation: Independent outbreak evidence supports P. aeruginosa as a recurrent etiologic pathogen in water-associated folliculitis.
- name: Malassezia
  infectious_agent_term:
    preferred_term: Malassezia
    term:
      id: NCBITaxon:55193
      label: Malassezia
  description: Lipophilic yeast associated with symptomatic follicular eruption.
  evidence:
  - reference: PMID:36912427
    reference_title: "Position statement: Recommendations on the diagnosis and treatment of Malassezia folliculitis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Malassezia folliculitis appears when the benign colonization of the hair follicles, by the Malassezia yeasts, becomes symptomatic with pruritic papules and pustules."
    explanation: Position statement directly describes Malassezia-associated folliculitis mechanism and clinical morphology.
- name: Demodex mites
  infectious_agent_term:
    preferred_term: Demodex
    term:
      id: NCBITaxon:188544
      label: Demodex
  description: Demodex mites are associated with inflammatory follicular histopathology.
  evidence:
  - reference: PMID:8989930
    reference_title: "Demodex-associated folliculitis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Demodex mites were found in 42% of follicles with inflammation, but in just 10% of the follicles without inflammation."
    explanation: Supports association between Demodex mites and human follicular inflammation.
prevalence:
- population: General population
  notes: True incidence is likely underestimated due to under-presentation for care.
  evidence:
  - reference: PMID:22639852
    reference_title: "First step in the differential diagnosis of folliculitis: cytology."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The incidence of folliculitis is unknown because most patients only consult a doctor in cases of increasing lesions."
    explanation: Review explicitly states incidence is unknown and likely underestimated.
progression:
- phase: Exposure-to-eruption interval in hot-tub folliculitis
  incubation_days: "0.3-2"
  notes: Fractional-day encoding (0.3-2) represents an approximately 8-48 hour onset window after contaminated water exposure.
  evidence:
  - reference: PMID:6402527
    reference_title: "Hot tub dermatitis: a familial outbreak of Pseudomonas folliculitis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Pseudomonas folliculitis resulting from the use of spa pools, whirlpools, and hot tubs is a newly described disease that typically develops 8 to 48 hours after exposure in a contaminated facility."
    explanation: Defines the incubation window for water-exposure-associated folliculitis.
  - reference: PMID:6828809
    reference_title: "Pseudomonas folliculitis: an outbreak and review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Thirty-seven (62%) of 60 members who used the swimming pool on these two days developed a papulopustular rash within eight hours to five days after swimming in the pool."
    explanation: Adds cohort-level timing evidence and supports a broader post-exposure onset window in outbreak settings.
- phase: Uncomplicated hot-tub folliculitis recovery
  duration_days: "7-10"
  notes: Many uncomplicated cases are self-limited if re-exposure is avoided.
  evidence:
  - reference: PMID:6402527
    reference_title: "Hot tub dermatitis: a familial outbreak of Pseudomonas folliculitis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Although the eruption usually resolves spontaneously within 7 to 10 days, proper maintenance of equipment and adequate disinfectant levels are necessary to prevent its recurrence."
    explanation: Describes expected spontaneous resolution timeline and recurrence prevention.
- phase: Antifungal treatment response in Malassezia folliculitis
  duration_days: "14-27"
  notes: Mean improvement time is shorter with oral itraconazole than topical ketoconazole in one cohort.
  evidence:
  - reference: PMID:27581777
    reference_title: "Treatment Outcomes for Malassezia Folliculitis in theDermatology Department of a University Hospital in Japan."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The mean period required for improvement was 27±16 days in 37 patients receiving the topical antifungal agent and 14±4 days in the 7 patients receiving the systemic antifungal agent."
    explanation: Provides quantitative treatment-response timing for a major folliculitis subtype.
- phase: Depth progression in staphylococcal folliculocentric infection
  notes: Staphylococcal follicular infection can remain superficial or progress to deeper furunculosis/carbuncle involvement.
  evidence:
  - reference: PMID:11980459
    reference_title: "Skin and soft tissue infection."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Folliculitis, furunculosis and carbuncle are folliculocentric infections caused by S. aureus involving the variable depth and extent of the follicle(s) and surrounding tissue."
    explanation: Supports depth-wise clinical progression within the staphylococcal folliculocentric infection spectrum.
  - reference: PMID:15482221
    reference_title: "Treatment of staphylococcal scalded skin syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "S. aureus is one of the most common causes of skin infection, giving rise to folliculitis, furunculosis, carbuncles, ecthyma, impetigo, cellulitis and abscesses."
    explanation: Independent support for the progression continuum from folliculitis to deeper staphylococcal infections.
- phase: Post-antibiotic emergence of gram-negative folliculitis
  notes: Gram-negative folliculitis commonly emerges after prolonged broad-spectrum antibiotic exposure in acne or rosacea.
  evidence:
  - reference: PMID:10321942
    reference_title: "Bacteriologic and immunologic aspects of gram-negative folliculitis: a study of 46 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Gram-negative folliculitis is an infection with gram-negative rods that most often occurs as a complication of prolonged broad-spectrum antibiotic therapy in patients suffering from acne and rosacea."
    explanation: Supports an antibiotic-associated progression pattern for gram-negative folliculitis.
- phase: Sustained remission after targeted treatment of gram-negative folliculitis
  duration: 4-48 months without recurrence after stopping effective systemic therapy in one follow-up cohort.
  evidence:
  - reference: PMID:6333214
    reference_title: "Gram-negative folliculitis. Follow-up observations in 20 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The systemic antibiotic therapy was discontinued after varying periods and the infection remained clear without further treatment for four to 48 months."
    explanation: Provides follow-up evidence for longer-term post-treatment course in gram-negative folliculitis.
pathophysiology:
- name: Staphylococcus aureus follicular colonization
  description: >
    S. aureus colonization of hair follicles is a common proximal trigger for
    infectious folliculitis.
  locations:
  - preferred_term: hair follicle
    term:
      id: UBERON:0002073
      label: hair follicle
  downstream:
  - target: Staphylococcal virulence factor activity
    description: Colonization permits expression of bacterial factors that promote tissue invasion and immune modulation.
    evidence:
    - reference: PMID:22639852
      reference_title: "First step in the differential diagnosis of folliculitis: cytology."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "There are various infectious and non-infectious causes of folliculitis, and the most common causative agent is Staphylococcus aureus."
      explanation: Supports frequent S. aureus follicular involvement as an upstream event in infectious folliculitis.
  evidence:
  - reference: PMID:22639852
    reference_title: "First step in the differential diagnosis of folliculitis: cytology."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "There are various infectious and non-infectious causes of folliculitis, and the most common causative agent is Staphylococcus aureus."
    explanation: Supports S. aureus as an upstream and common etiologic mechanism.
- name: Staphylococcal virulence factor activity
  description: >
    S. aureus expresses cytolytic, superantigenic, and immune-evasion factors
    that enable progression from colonization to tissue-level inflammation.
  downstream:
  - target: Keratinocyte innate immune activation
    description: Virulence factors trigger early host epithelial danger responses.
    evidence:
    - reference: DOI:10.3390/antibiotics12030557
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "In order to cause skin infections, S. aureus employs a host of virulence factors including cytolytic proteins, superantigenic factors, cell wall-anchored proteins, and molecules used for immune evasion."
      explanation: Provides molecular-level support for a discrete virulence-factor stage between colonization and host inflammation.
  evidence:
  - reference: DOI:10.3390/antibiotics12030557
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In order to cause skin infections, S. aureus employs a host of virulence factors including cytolytic proteins, superantigenic factors, cell wall-anchored proteins, and molecules used for immune evasion."
    explanation: Supports a biomolecular virulence stage in staphylococcal folliculitis.
- name: Keratinocyte innate immune activation
  description: >
    Keratinocytes act as early epithelial sentinels and initiate innate immune
    responses after bacterial challenge.
  cell_types:
  - preferred_term: keratinocyte
    term:
      id: CL:0000312
      label: keratinocyte
  biological_processes:
  - preferred_term: response to bacterium
    term:
      id: GO:0009617
      label: response to bacterium
  downstream:
  - target: Neutrophil recruitment and activation
    description: Early epithelial immune activation precedes and supports neutrophil-dominant inflammatory influx.
    evidence:
    - reference: DOI:10.3390/antibiotics12030557
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The immune response to S. aureus SSTIs involves initial responders such as keratinocytes and neutrophils, which are supported by dendritic cells and T-lymphocytes later during infection."
      explanation: Supports a sequential cellular response beginning with keratinocyte involvement and progressing to neutrophilic inflammation.
  evidence:
  - reference: DOI:10.3390/antibiotics12030557
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The immune response to S. aureus SSTIs involves initial responders such as keratinocytes and neutrophils, which are supported by dendritic cells and T-lymphocytes later during infection."
    explanation: Supports keratinocyte participation as an early cellular event in skin infection pathophysiology.
- name: Neutrophil recruitment and activation
  description: >
    Neutrophils are recruited and activated, amplifying follicular inflammatory
    injury.
  cell_types:
  - preferred_term: neutrophil
    term:
      id: CL:0000775
      label: neutrophil
  biological_processes:
  - preferred_term: neutrophil activation
    term:
      id: GO:0042119
      label: neutrophil activation
  downstream:
  - target: Acute suppurative follicular inflammation
    description: Activated neutrophils drive suppurative follicular pathology.
    evidence:
    - reference: DOI:10.3390/antibiotics12030557
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The immune response to S. aureus SSTIs involves initial responders such as keratinocytes and neutrophils, which are supported by dendritic cells and T-lymphocytes later during infection."
      explanation: Supports neutrophils as key cellular effectors linking upstream microbial events to acute suppurative inflammation.
  evidence:
  - reference: DOI:10.3390/antibiotics12030557
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The immune response to S. aureus SSTIs involves initial responders such as keratinocytes and neutrophils, which are supported by dendritic cells and T-lymphocytes later during infection."
    explanation: Supports neutrophil-centric immune amplification in staphylococcal folliculitis mechanisms.
- name: Acute suppurative follicular inflammation
  description: >
    Follicular inflammation progresses to acute suppuration with histologic
    evidence of neutrophil-rich tissue injury.
  biological_processes:
  - preferred_term: inflammatory response
    term:
      id: GO:0006954
      label: inflammatory response
  downstream:
  - target: Erythematous papules
    description: Suppurative follicular inflammation produces papular lesions.
    evidence:
    - reference: PMID:6402527
      reference_title: "Hot tub dermatitis: a familial outbreak of Pseudomonas folliculitis."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The eruption consists of pruritic papules, papulopustules, nodules, and urticarial lesions on the trunk and extremities."
      explanation: Supports papules as a direct downstream clinical manifestation.
  - target: Pustules
    description: Purulent follicular lesions emerge with ongoing suppurative inflammation.
    evidence:
    - reference: PMID:6402527
      reference_title: "Hot tub dermatitis: a familial outbreak of Pseudomonas folliculitis."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The eruption consists of pruritic papules, papulopustules, nodules, and urticarial lesions on the trunk and extremities."
      explanation: Supports pustules as a direct clinical output of acute suppurative follicular inflammation.
  - target: Pruritus
    description: Inflammatory follicular lesions frequently produce itch.
    evidence:
    - reference: PMID:6402527
      reference_title: "Hot tub dermatitis: a familial outbreak of Pseudomonas folliculitis."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The eruption consists of pruritic papules, papulopustules, nodules, and urticarial lesions on the trunk and extremities."
      explanation: Supports itch as a downstream symptom of inflammatory follicular lesions.
  evidence:
  - reference: PMID:6402527
    reference_title: "Hot tub dermatitis: a familial outbreak of Pseudomonas folliculitis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Skin biopsies showed an acute, suppurative folliculitis and dermal abscess formation."
    explanation: Histopathology confirms the suppurative inflammatory stage.
- name: Non-staphylococcal microbial follicular colonization
  description: >
    Gram-negative bacterial, fungal, parasitic, and viral pathogens can also
    colonize follicles and converge on inflammatory papulopustular disease.
  locations:
  - preferred_term: hair follicle
    term:
      id: UBERON:0002073
      label: hair follicle
  downstream:
  - target: Acute suppurative follicular inflammation
    description: Diverse folliculotropic pathogens can trigger convergent inflammatory pathways.
    evidence:
    - reference: PMID:22639852
      reference_title: "First step in the differential diagnosis of folliculitis: cytology."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "In addition, several Gram-negative bacterial, fungal, parasitic, and viral pathogens can cause follicular papules and pustules."
      explanation: Supports multi-pathogen convergence on inflammatory follicular disease.
  evidence:
  - reference: PMID:22639852
    reference_title: "First step in the differential diagnosis of folliculitis: cytology."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In addition, several Gram-negative bacterial, fungal, parasitic, and viral pathogens can cause follicular papules and pustules."
    explanation: Supports a pathogen-diverse upstream entry point into folliculitis pathophysiology.
- name: Prolonged broad-spectrum antibiotic exposure in acne or rosacea
  description: >
    Extended broad-spectrum antibiotic exposure can create conditions that favor
    gram-negative follicular infection.
  downstream:
  - target: Gram-negative follicular overgrowth and infection
    description: Antibiotic pressure can precede overgrowth of gram-negative folliculotropic organisms.
    evidence:
    - reference: PMID:10321942
      reference_title: "Bacteriologic and immunologic aspects of gram-negative folliculitis: a study of 46 patients."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Gram-negative folliculitis is an infection with gram-negative rods that most often occurs as a complication of prolonged broad-spectrum antibiotic therapy in patients suffering from acne and rosacea."
      explanation: Supports antibiotic-associated emergence of gram-negative folliculitis as a distinct mechanistic step.
  evidence:
  - reference: PMID:10321942
    reference_title: "Bacteriologic and immunologic aspects of gram-negative folliculitis: a study of 46 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Gram-negative folliculitis is an infection with gram-negative rods that most often occurs as a complication of prolonged broad-spectrum antibiotic therapy in patients suffering from acne and rosacea."
    explanation: Supports prolonged antibiotic exposure as an upstream event in gram-negative folliculitis.
- name: Gram-negative follicular overgrowth and infection
  description: >
    Gram-negative organisms including Klebsiella, Escherichia coli,
    Enterobacter, and Proteus can overgrow and infect follicles.
  locations:
  - preferred_term: hair follicle
    term:
      id: UBERON:0002073
      label: hair follicle
  downstream:
  - target: Acute suppurative follicular inflammation
    description: Gram-negative follicular infection converges on suppurative follicular inflammation.
    evidence:
    - reference: PMID:10321942
      reference_title: "Bacteriologic and immunologic aspects of gram-negative folliculitis: a study of 46 patients."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The gram-negative organisms most frequently cultivated from nares, facial skin, and pustules were Klebsiella spp., Escherichia coli, Enterobacter spp., and Proteus spp."
      explanation: Supports pathogen-specific follicular infection in gram-negative folliculitis.
  evidence:
  - reference: PMID:10321942
    reference_title: "Bacteriologic and immunologic aspects of gram-negative folliculitis: a study of 46 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The gram-negative organisms most frequently cultivated from nares, facial skin, and pustules were Klebsiella spp., Escherichia coli, Enterobacter spp., and Proteus spp."
    explanation: Supports a discrete pathogen-overgrowth stage in gram-negative folliculitis.
- name: Demodex follicular colonization
  description: >
    Demodex mites are present in a subset of follicles and are associated with
    inflammatory follicular histopathology.
  locations:
  - preferred_term: hair follicle
    term:
      id: UBERON:0002073
      label: hair follicle
  downstream:
  - target: Demodex-associated follicular inflammation
    description: Colonized follicles show higher rates of histologic inflammation.
    evidence:
    - reference: PMID:8989930
      reference_title: "Demodex-associated folliculitis."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Demodex mites were found in 42% of follicles with inflammation, but in just 10% of the follicles without inflammation."
      explanation: Supports a quantitative association between Demodex presence and follicular inflammation.
  evidence:
  - reference: PMID:8989930
    reference_title: "Demodex-associated folliculitis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Demodex mites were found in 42% of follicles with inflammation, but in just 10% of the follicles without inflammation."
    explanation: Supports Demodex colonization as a candidate upstream event in follicular inflammation.
- name: Demodex-associated follicular inflammation
  description: >
    Follicles containing Demodex mites frequently show inflammatory changes,
    supporting a mite-associated inflammatory folliculitis pathway.
  evidence:
  - reference: PMID:8989930
    reference_title: "Demodex-associated folliculitis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Eighty-three percent of follicles with Demodex showed inflammation."
    explanation: Supports mite-associated follicular inflammation as a discrete pathophysiologic event.
- name: Malassezia follicular colonization
  description: >
    Malassezia yeast exists as part of the normal follicular mycobiome before
    symptomatic disease develops.
  locations:
  - preferred_term: hair follicle
    term:
      id: UBERON:0002073
      label: hair follicle
  downstream:
  - target: Pathogenic Malassezia transition with virulence factor production
    description: Commensal colonization can shift toward pathogenic behavior under permissive host-agent conditions.
    evidence:
    - reference: PMID:36912427
      reference_title: "Position statement: Recommendations on the diagnosis and treatment of Malassezia folliculitis."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Malassezia is a lipophilic yeast that is a part of the human mycobiome."
      explanation: Supports a commensal baseline state preceding symptomatic Malassezia folliculitis.
  evidence:
  - reference: PMID:36912427
    reference_title: "Position statement: Recommendations on the diagnosis and treatment of Malassezia folliculitis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Malassezia is a lipophilic yeast that is a part of the human mycobiome."
    explanation: Establishes baseline commensal follicular colonization by Malassezia.
- name: Pathogenic Malassezia transition with virulence factor production
  description: >
    Host-agent interactions can drive Malassezia transition from commensal to
    pathogenic states with production of inflammatory virulence factors.
  downstream:
  - target: Malassezia-associated follicular inflammation
    description: Virulence factor production promotes symptomatic follicular inflammatory disease.
    evidence:
    - reference: PMID:35751534
      reference_title: "Malassezia virulence factors and their role in dermatological disorders."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "This phenomenon is influenced by a unique host-agent interaction that triggers the production of several virulence factors, such as indoles, reactive oxygen species, azelaic acid, hyphae formation, and biofilm formation."
      explanation: Supports a biomolecular transition stage characterized by virulence factor induction.
  evidence:
  - reference: PMID:35751534
    reference_title: "Malassezia virulence factors and their role in dermatological disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "However, in certain conditions and individuals, it may transform into a pathogenic yeast with multiple associated dermatological disorders and various clinical manifestations."
    explanation: Supports commensal-to-pathogenic transition in Malassezia disease biology.
- name: Malassezia-associated follicular inflammation
  description: >
    Symptomatic Malassezia folliculitis manifests as inflammatory pruritic
    papulopustular follicular lesions.
  downstream:
  - target: Pustules
    description: Malassezia-driven inflammation contributes to follicular pustule formation.
    evidence:
    - reference: PMID:36912427
      reference_title: "Position statement: Recommendations on the diagnosis and treatment of Malassezia folliculitis."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Malassezia folliculitis appears when the benign colonization of the hair follicles, by the Malassezia yeasts, becomes symptomatic with pruritic papules and pustules."
      explanation: Supports pustule formation downstream of symptomatic Malassezia follicular inflammation.
  - target: Pruritus
    description: Malassezia-associated inflammatory lesions are characteristically pruritic.
    evidence:
    - reference: PMID:36912427
      reference_title: "Position statement: Recommendations on the diagnosis and treatment of Malassezia folliculitis."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Malassezia folliculitis appears when the benign colonization of the hair follicles, by the Malassezia yeasts, becomes symptomatic with pruritic papules and pustules."
      explanation: Supports itch as a downstream manifestation of Malassezia follicular inflammation.
  evidence:
  - reference: PMID:36912427
    reference_title: "Position statement: Recommendations on the diagnosis and treatment of Malassezia folliculitis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Malassezia folliculitis appears when the benign colonization of the hair follicles, by the Malassezia yeasts, becomes symptomatic with pruritic papules and pustules."
    explanation: Supports symptomatic inflammatory transition in Malassezia folliculitis.
- name: Eosinophilic follicular inflammation in advanced HIV
  description: >
    In advanced HIV infection, a culture-negative eosinophilic folliculitis
    pattern can occur with chronic pruritic disease.
  cell_types:
  - preferred_term: eosinophil
    term:
      id: CL:0000771
      label: eosinophil
  downstream:
  - target: Pruritus
    description: Eosinophilic inflammatory lesions are strongly pruritic.
    evidence:
    - reference: PMID:1671328
      reference_title: "Human immunodeficiency virus-associated eosinophilic folliculitis. A unique dermatosis associated with advanced human immunodeficiency virus infection."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "These observations demonstrate that HIV-associated eosinophilic folliculitis is a unique HIV-related cutaneous disorder that is characterized by a culture-negative, chronic, pruritic folliculitis and a characteristic histopathologic picture."
      explanation: Supports pruritus as a downstream hallmark of eosinophilic follicular inflammation.
  evidence:
  - reference: PMID:1671328
    reference_title: "Human immunodeficiency virus-associated eosinophilic folliculitis. A unique dermatosis associated with advanced human immunodeficiency virus infection."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These observations demonstrate that HIV-associated eosinophilic folliculitis is a unique HIV-related cutaneous disorder that is characterized by a culture-negative, chronic, pruritic folliculitis and a characteristic histopathologic picture."
    explanation: Defines an immunologic, eosinophilic folliculitis mechanism distinct from pyogenic bacterial disease.
- name: Folliculitis decalvans follicular dysbiosis
  description: >
    Folliculitis decalvans exhibits a disease-associated shift in follicular
    bacterial community structure.
  subtypes:
  - Folliculitis decalvans
  locations:
  - preferred_term: hair follicle
    term:
      id: UBERON:0002073
      label: hair follicle
  downstream:
  - target: Impaired antibacterial cytokine response in folliculitis decalvans
    description: Dysbiotic follicular microbiota is associated with abnormal host immune response profiles.
    evidence:
    - reference: PMID:36716709
      reference_title: "Folliculitis Decalvans Has a Heterogeneous Microbiological Signature and Impaired Immunological Response."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "β-diversity analysis showed statistically significant differences regarding bacteria comparing follicular microbiota of healthy and FD-affected hairs."
      explanation: Supports a discrete microbiome-disruption stage in folliculitis decalvans pathogenesis.
  evidence:
  - reference: PMID:36716709
    reference_title: "Folliculitis Decalvans Has a Heterogeneous Microbiological Signature and Impaired Immunological Response."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "CONCLUSION: FD hair follicles have a specific heterogenous follicular bacterial microbiota signature."
    explanation: Supports the presence of subtype-specific follicular dysbiosis in folliculitis decalvans.
- name: Impaired antibacterial cytokine response in folliculitis decalvans
  description: >
    Patients with folliculitis decalvans show reduced cytokine responses to
    bacterial stimulation.
  subtypes:
  - Folliculitis decalvans
  downstream:
  - target: Neutrophilic scarring follicular inflammation in folliculitis decalvans
    description: Aberrant immune response contributes to persistent neutrophilic inflammatory disease with scarring outcomes.
    evidence:
    - reference: PMID:36716709
      reference_title: "Folliculitis Decalvans Has a Heterogeneous Microbiological Signature and Impaired Immunological Response."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "IL-10, TNF-α, and IL-6 levels were significantly decreased in patients after incubation with various strains of bacteria compared with controls."
      explanation: Supports a molecular immune-dysregulation stage downstream of dysbiosis and upstream of chronic inflammatory damage.
  evidence:
  - reference: PMID:36716709
    reference_title: "Folliculitis Decalvans Has a Heterogeneous Microbiological Signature and Impaired Immunological Response."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "IL-10, TNF-α, and IL-6 levels were significantly decreased in patients after incubation with various strains of bacteria compared with controls."
    explanation: Supports impaired antibacterial cytokine signaling as a mechanistic event in folliculitis decalvans.
  - reference: clinicaltrials:NCT07268534
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "FD is a non-curable disease for which inflammatory pathways involving several cytokines as TNF, IL1β, IL8, TGFβ, IL12 and 23, could also play a role."
    explanation: Trial rationale provides additional human-clinical support for cytokine pathway involvement in FD pathobiology.
  - reference: PMID:18715292
    reference_title: "Folliculitis decalvans."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Staphylococcus aureus and a deficient host immune response seem to play an important role in the development of this disfiguring scalp disease."
    explanation: Supports host-immune dysfunction as a central mechanistic factor in FD pathogenesis.
- name: Neutrophilic scarring follicular inflammation in folliculitis decalvans
  description: >
    Folliculitis decalvans is characterized by chronic neutrophilic follicular
    inflammation with scarring progression.
  subtypes:
  - Folliculitis decalvans
  cell_types:
  - preferred_term: neutrophil
    term:
      id: CL:0000775
      label: neutrophil
  downstream:
  - target: Alopecia
    description: Progressive scarring follicular inflammation causes permanent hair loss.
    evidence:
    - reference: PMID:36716709
      reference_title: "Folliculitis Decalvans Has a Heterogeneous Microbiological Signature and Impaired Immunological Response."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "BACKGROUND: Folliculitis decalvans (FD) is a rare primary neutrophilic scarring alopecia whose etiology has not been completely elucidated yet."
      explanation: Supports downstream linkage from neutrophilic scarring inflammation to alopecia in FD.
  evidence:
  - reference: PMID:36716709
    reference_title: "Folliculitis Decalvans Has a Heterogeneous Microbiological Signature and Impaired Immunological Response."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "BACKGROUND: Folliculitis decalvans (FD) is a rare primary neutrophilic scarring alopecia whose etiology has not been completely elucidated yet."
    explanation: Supports a distinct chronic neutrophilic scarring-inflammatory stage in FD.
  - reference: PMID:18715292
    reference_title: "Folliculitis decalvans."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Histology displays a mainly neutrophilic inflammatory infiltrate in early lesions and additionally lymphocytes and plasma cells in advanced lesions."
    explanation: Adds direct histologic support for neutrophil-dominant early FD inflammation with chronic inflammatory progression.
- name: EGFR pathway disruption in follicular stem-cell niche
  description: >
    EGFR pathway loss removes protective signaling in the follicular stem-cell
    niche and predisposes to inflammatory tissue injury.
  subtypes:
  - EGFR inhibitor-induced folliculitis decalvans
  downstream:
  - target: JAK-STAT1 pathway hypersensitivity in EGFR-deficient follicles
    description: EGFR pathway disruption triggers cell-intrinsic hypersensitivity to inflammatory signaling.
    evidence:
    - reference: PMID:39521937
      reference_title: "JAK-STAT1 as therapeutic target for EGFR deficiency-associated inflammation and scarring alopecia."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "In this study, we demonstrated the protective role of hair follicle-specific epidermal growth factor receptor (EGFR) against scarring hair follicle destruction."
      explanation: Supports a discrete upstream event where EGFR signaling protects against scarring follicular injury.
  evidence:
  - reference: PMID:39521937
    reference_title: "JAK-STAT1 as therapeutic target for EGFR deficiency-associated inflammation and scarring alopecia."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In this study, we demonstrated the protective role of hair follicle-specific epidermal growth factor receptor (EGFR) against scarring hair follicle destruction."
    explanation: Supports loss of EGFR-mediated follicular protection as an initiating mechanistic event.
- name: JAK-STAT1 pathway hypersensitivity in EGFR-deficient follicles
  description: >
    EGFR-deficient follicular cells develop heightened JAK-STAT1 signaling
    sensitivity.
  subtypes:
  - EGFR inhibitor-induced folliculitis decalvans
  downstream:
  - target: Interferon-γ CD8 T-cell and NK-cell inflammatory amplification
    description: Heightened JAK-STAT1 signaling synergizes with interferon-γ-driven lymphoid inflammation.
    evidence:
    - reference: PMID:39521937
      reference_title: "JAK-STAT1 as therapeutic target for EGFR deficiency-associated inflammation and scarring alopecia."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Mechanistically, disruption of EGFR signaling generated a cell-intrinsic hypersensitivity within the JAK-STAT1 pathway, which, synergistically with interferon gamma expressing CD8 T-cell and NK-cell-mediated inflammation, compromised the stem cell niche."
      explanation: Supports a specific intracellular signaling step linking EGFR loss to amplified immune-mediated follicular injury.
  evidence:
  - reference: PMID:39521937
    reference_title: "JAK-STAT1 as therapeutic target for EGFR deficiency-associated inflammation and scarring alopecia."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Mechanistically, disruption of EGFR signaling generated a cell-intrinsic hypersensitivity within the JAK-STAT1 pathway, which, synergistically with interferon gamma expressing CD8 T-cell and NK-cell-mediated inflammation, compromised the stem cell niche."
    explanation: Supports JAK-STAT1 hypersensitivity as a distinct biomolecular event.
- name: Interferon-γ CD8 T-cell and NK-cell inflammatory amplification
  description: >
    Interferon-γ-expressing CD8 T cells and NK cells amplify follicular
    inflammatory injury in EGFR-deficient settings.
  subtypes:
  - EGFR inhibitor-induced folliculitis decalvans
  downstream:
  - target: Stem-cell niche compromise and scarring follicle destruction
    description: Inflammatory amplification damages the follicular stem-cell niche and drives scarring destruction.
    evidence:
    - reference: PMID:39521937
      reference_title: "JAK-STAT1 as therapeutic target for EGFR deficiency-associated inflammation and scarring alopecia."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Mechanistically, disruption of EGFR signaling generated a cell-intrinsic hypersensitivity within the JAK-STAT1 pathway, which, synergistically with interferon gamma expressing CD8 T-cell and NK-cell-mediated inflammation, compromised the stem cell niche."
      explanation: Supports immune-cell-mediated amplification as an intermediate causal step before structural follicular destruction.
  evidence:
  - reference: PMID:39521937
    reference_title: "JAK-STAT1 as therapeutic target for EGFR deficiency-associated inflammation and scarring alopecia."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Mechanistically, disruption of EGFR signaling generated a cell-intrinsic hypersensitivity within the JAK-STAT1 pathway, which, synergistically with interferon gamma expressing CD8 T-cell and NK-cell-mediated inflammation, compromised the stem cell niche."
    explanation: Supports a lymphoid inflammatory amplification stage in EGFR inhibitor-associated folliculitis biology.
- name: Stem-cell niche compromise and scarring follicle destruction
  description: >
    Compromised follicular stem-cell niche integrity and associated signaling
    changes culminate in scarring follicular injury.
  subtypes:
  - EGFR inhibitor-induced folliculitis decalvans
  downstream:
  - target: Alopecia
    description: Scarring follicular destruction leads to permanent hair loss phenotypes.
    evidence:
    - reference: PMID:39521937
      reference_title: "JAK-STAT1 as therapeutic target for EGFR deficiency-associated inflammation and scarring alopecia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Skin biopsies from EGFR inhibitor-treated and cicatricial alopecia patients revealed an active JAK-STAT1 signaling signature along with upregulation of antigen presentation and downregulation of key components of the EGFR pathway."
      explanation: Human biopsy evidence supports terminal scarring-destruction biology linked to alopecia.
  evidence:
  - reference: PMID:39521937
    reference_title: "JAK-STAT1 as therapeutic target for EGFR deficiency-associated inflammation and scarring alopecia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Skin biopsies from EGFR inhibitor-treated and cicatricial alopecia patients revealed an active JAK-STAT1 signaling signature along with upregulation of antigen presentation and downregulation of key components of the EGFR pathway."
    explanation: Supports endpoint follicular destruction biology with clinically relevant human tissue evidence.
phenotypes:
- name: Erythematous papules
  description: Papular follicular eruption on hair-bearing skin, especially trunk and extremities in some subtypes.
  phenotype_term:
    preferred_term: erythematous papule
    term:
      id: HP:0030350
      label: Erythematous papule
  evidence:
  - reference: PMID:6402527
    reference_title: "Hot tub dermatitis: a familial outbreak of Pseudomonas folliculitis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The eruption consists of pruritic papules, papulopustules, nodules, and urticarial lesions on the trunk and extremities."
    explanation: Directly supports papular morphology and common distribution.
- name: Pustules
  description: Follicular pustules are common in infectious and yeast-associated forms.
  phenotype_term:
    preferred_term: pustule
    term:
      id: HP:0200039
      label: Pustule
  evidence:
  - reference: PMID:22639852
    reference_title: "First step in the differential diagnosis of folliculitis: cytology."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In addition, several Gram-negative bacterial, fungal, parasitic, and viral pathogens can cause follicular papules and pustules."
    explanation: Supports pustules as a core lesion type across infectious etiologies.
  - reference: PMID:18715292
    reference_title: "Folliculitis decalvans."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Clinically, the lesions present with follicular pustules, lack of ostia, diffuse and perifollicular erythema, follicular tufting, and, oftentimes, hemorrhagic crusts and erosions."
    explanation: Provides subtype-specific clinical evidence for pustules in folliculitis decalvans.
- name: Pruritus
  description: Itching is common and can be severe in eosinophilic and Malassezia-associated variants.
  phenotype_term:
    preferred_term: pruritus
    term:
      id: HP:0000989
      label: Pruritus
  evidence:
  - reference: PMID:6402527
    reference_title: "Hot tub dermatitis: a familial outbreak of Pseudomonas folliculitis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The eruption consists of pruritic papules, papulopustules, nodules, and urticarial lesions on the trunk and extremities."
    explanation: Confirms itch as a frequent symptom in symptomatic follicular eruptions.
- name: Low-grade fever
  description: Some cases of hot-tub folliculitis include mild constitutional symptoms.
  phenotype_term:
    preferred_term: fever
    term:
      id: HP:0001945
      label: Fever
  evidence:
  - reference: PMID:2307901
    reference_title: "Hot tub (Pseudomonas) folliculitis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The condition is characterized by painful, papulopustular skin lesions often accompanied by low-grade fever, malaise, and other systemic symptoms."
    explanation: Supports fever as a contextual phenotype in Pseudomonas-associated folliculitis.
- name: Alopecia
  description: Scarring alopecia can occur in chronic folliculitis decalvans/tufted hair folliculitis.
  subtype: Folliculitis decalvans
  phenotype_term:
    preferred_term: alopecia
    term:
      id: HP:0001596
      label: Alopecia
  evidence:
  - reference: PMID:41146582
    reference_title: "Management of Folliculitis Decalvans: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Folliculitis decalvans (FD) and Tufted Hair Folliculitis (THF) present with recurrent episodes of follicular inflammation, pustules and crusting, predominantly of the scalp, leading to scarring alopecia."
    explanation: Supports alopecia as a clinically important sequela in scarring folliculitis subtypes.
  - reference: PMID:36716709
    reference_title: "Folliculitis Decalvans Has a Heterogeneous Microbiological Signature and Impaired Immunological Response."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Folliculitis decalvans (FD) is a rare primary neutrophilic scarring alopecia whose etiology has not been completely elucidated yet."
    explanation: Provides independent support that scarring alopecia is a defining phenotype of folliculitis decalvans.
histopathology:
- name: Acute suppurative folliculitis with dermal abscess formation
  description: Biopsy in hot-tub folliculitis demonstrates acute neutrophilic suppurative folliculitis with dermal abscess formation.
  subtype: Pseudomonas hot-tub folliculitis
  evidence:
  - reference: PMID:6402527
    reference_title: "Hot tub dermatitis: a familial outbreak of Pseudomonas folliculitis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Skin biopsies showed an acute, suppurative folliculitis and dermal abscess formation."
    explanation: Direct histopathology evidence for suppurative inflammatory follicular injury in pseudomonal folliculitis.
- name: Eosinophilic culture-negative chronic folliculitis pattern
  description: HIV-associated eosinophilic folliculitis shows a characteristic histopathologic pattern with chronic pruritic culture-negative disease.
  subtype: HIV-associated eosinophilic folliculitis
  evidence:
  - reference: PMID:1671328
    reference_title: "Human immunodeficiency virus-associated eosinophilic folliculitis. A unique dermatosis associated with advanced human immunodeficiency virus infection."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These observations demonstrate that HIV-associated eosinophilic folliculitis is a unique HIV-related cutaneous disorder that is characterized by a culture-negative, chronic, pruritic folliculitis and a characteristic histopathologic picture."
    explanation: Supports a distinct eosinophilic histopathologic pattern in HIV-associated folliculitis.
- name: Demodex-associated follicular inflammation on histology
  description: Follicles containing Demodex are frequently inflamed, supporting a mite-associated inflammatory histologic phenotype.
  subtype: Demodex-associated folliculitis
  evidence:
  - reference: PMID:8989930
    reference_title: "Demodex-associated folliculitis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Eighty-three percent of follicles with Demodex showed inflammation."
    explanation: Supports Demodex-associated inflammatory histopathologic findings.
- name: Neutrophilic scarring alopecia pattern
  description: Folliculitis decalvans is characterized histopathologically within the primary neutrophilic scarring alopecia spectrum.
  subtype: Folliculitis decalvans
  evidence:
  - reference: PMID:36716709
    reference_title: "Folliculitis Decalvans Has a Heterogeneous Microbiological Signature and Impaired Immunological Response."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "BACKGROUND: Folliculitis decalvans (FD) is a rare primary neutrophilic scarring alopecia whose etiology has not been completely elucidated yet."
    explanation: Supports a chronic neutrophilic scarring histopathology context for folliculitis decalvans.
  - reference: PMID:18715292
    reference_title: "Folliculitis decalvans."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Histology displays a mainly neutrophilic inflammatory infiltrate in early lesions and additionally lymphocytes and plasma cells in advanced lesions."
    explanation: Adds direct histopathology detail supporting mixed-stage inflammatory infiltrates in FD.
biochemical: []
genetic: []
environmental:
- name: Contaminated recreational water exposure
  description: Exposure to inadequately disinfected hot tubs/spa pools can trigger Pseudomonas folliculitis.
  effect: Triggers acute exposure-associated folliculitis
  evidence:
  - reference: PMID:6402527
    reference_title: "Hot tub dermatitis: a familial outbreak of Pseudomonas folliculitis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Pseudomonas folliculitis resulting from the use of spa pools, whirlpools, and hot tubs is a newly described disease that typically develops 8 to 48 hours after exposure in a contaminated facility."
    explanation: Supports contaminated water exposure as an environmental trigger.
- name: Advanced HIV immunosuppression
  description: Low CD4 counts are associated with eosinophilic folliculitis in HIV infection.
  effect: Predisposes to chronic eosinophilic folliculitis phenotype
  evidence:
  - reference: PMID:1671328
    reference_title: "Human immunodeficiency virus-associated eosinophilic folliculitis. A unique dermatosis associated with advanced human immunodeficiency virus infection."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Of special importance, because it is associated with CD4 counts of less than 250 to 300 cells per cubic millimeter, eosinophilic folliculitis appears to be an important clinical marker of HIV infection and, particularly, of patients at increased risk of developing opportunistic infections."
    explanation: Supports severe HIV-associated immunosuppression as a major risk context.
treatments:
- name: Topical or systemic antibacterial therapy
  description: Antibacterial pharmacotherapy is commonly used for presumed bacterial folliculitis.
  treatment_term:
    preferred_term: pharmacotherapy
    term:
      id: MAXO:0000058
      label: pharmacotherapy
    qualifiers:
    - predicate:
        preferred_term: therapeutic procedure
        term:
          id: NCIT:C49236
          label: Therapeutic Procedure
      value:
        preferred_term: topical route of administration
        term:
          id: NCIT:C38304
          label: Topical Route of Administration
    - predicate:
        preferred_term: therapeutic procedure
        term:
          id: NCIT:C49236
          label: Therapeutic Procedure
      value:
        preferred_term: oral route of administration
        term:
          id: NCIT:C38288
          label: Oral Route of Administration
    - predicate:
        preferred_term: specify therapeutic agent
        term:
          id: NCIT:C157096
          label: Specify Therapeutic Agent
      value:
        preferred_term: antibiotic
        term:
          id: NCIT:C258
          label: Antibiotic
  evidence:
  - reference: PMID:22639852
    reference_title: "First step in the differential diagnosis of folliculitis: cytology."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Therefore, topical and/or systemic antibacterial treatment is recommended, but this involves the risk of being misused for months or even years."
    explanation: Review supports antibacterial treatment use while cautioning against prolonged empiric misuse.
  - reference: DOI:10.3390/antibiotics12030557
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Treatment for S. aureus SSTIs is usually oral therapy, with parenteral therapy reserved for severe presentations; it ranges from cephalosporins and penicillin agents such as oxacillin, which is generally used for methicillin-sensitive S. aureus (MSSA), to vancomycin for methicillin-resistant S. aureus (MRSA)."
    explanation: Adds contemporary treatment-stratification evidence for staphylococcal folliculitis-spectrum infections.
- name: Topical and systemic antifungal therapy for Malassezia folliculitis
  description: Ketoconazole cream and oral itraconazole are both effective options for Malassezia-associated disease.
  treatment_term:
    preferred_term: pharmacotherapy
    term:
      id: MAXO:0000058
      label: pharmacotherapy
    qualifiers:
    - predicate:
        preferred_term: therapeutic procedure
        term:
          id: NCIT:C49236
          label: Therapeutic Procedure
      value:
        preferred_term: topical route of administration
        term:
          id: NCIT:C38304
          label: Topical Route of Administration
    - predicate:
        preferred_term: therapeutic procedure
        term:
          id: NCIT:C49236
          label: Therapeutic Procedure
      value:
        preferred_term: oral route of administration
        term:
          id: NCIT:C38288
          label: Oral Route of Administration
    - predicate:
        preferred_term: specify therapeutic agent
        term:
          id: NCIT:C157096
          label: Specify Therapeutic Agent
      value:
        preferred_term: antifungal agent
        term:
          id: NCIT:C514
          label: Antifungal Agent
  evidence:
  - reference: PMID:27581777
    reference_title: "Treatment Outcomes for Malassezia Folliculitis in theDermatology Department of a University Hospital in Japan."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Treatment consisted of topical application of 2% ketoconazole cream or 100 mg oral itraconazole based on symptom severity and patients' preferences."
    explanation: Documents real-world topical and oral antifungal regimens.
  - reference: PMID:27581777
    reference_title: "Treatment Outcomes for Malassezia Folliculitis in theDermatology Department of a University Hospital in Japan."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The results were \"improved\" and the treatment was \"effective\" in all patients."
    explanation: Supports clinical effectiveness of both antifungal strategies in this cohort.
- name: Combination therapy for folliculitis decalvans/tufted hair folliculitis
  description: Combination regimens may provide better and longer responses than antibiotic monotherapy in scarring folliculitis subtypes.
  context: Folliculitis decalvans / tufted hair folliculitis
  treatment_term:
    preferred_term: pharmacotherapy
    term:
      id: MAXO:0000058
      label: pharmacotherapy
    qualifiers:
    - predicate:
        preferred_term: therapeutic procedure
        term:
          id: NCIT:C49236
          label: Therapeutic Procedure
      value:
        preferred_term: systemic therapy
        term:
          id: NCIT:C15698
          label: Systemic Therapy
    - predicate:
        preferred_term: specify therapeutic agent
        term:
          id: NCIT:C157096
          label: Specify Therapeutic Agent
      value:
        preferred_term: anti-infective agent
        term:
          id: NCIT:C254
          label: Anti-Infective Agent
  evidence:
  - reference: PMID:41146582
    reference_title: "Management of Folliculitis Decalvans: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Combination therapy with systemic antibiotics, topical, local and/or other systemic agents may provide the best outcome and longest DoE for FD/THF patients, with a greater role for biologic agents and laser therapy in their management."
    explanation: Systematic review supports multimodal treatment strategy for chronic scarring folliculitis variants.
  - reference: PMID:29864465
    reference_title: "Folliculitis decalvans: Effectiveness of therapies and prognostic factors in a multicenter series of 60 patients with long-term follow-up."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Treatment with rifampicin and clindamycin, tetracyclines, and intralesional steroids was the most effective."
    explanation: Multicenter long-term follow-up study provides specific evidence for effective combination regimens in folliculitis decalvans.
  - reference: clinicaltrials:NCT07268534
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Short-term efficacy rate of antibiotics is around 50-60%, but unfortunately, recurrences/relapses are occurring 5 to 7 months on average after stopping antibiotics, requiring their reintroduction/long-term use and potentially less efficacy/ecological harms."
    explanation: Supports limitations of antibiotic-only strategies and the need for alternative or adjunctive management approaches in FD.
- name: Adjunctive anti-inflammatory/phototherapy for HIV-associated eosinophilic folliculitis
  description: Symptom-directed therapies such as UVB and topical corticosteroids can improve HIV-associated eosinophilic folliculitis.
  context: HIV-associated eosinophilic folliculitis
  treatment_term:
    preferred_term: pharmacotherapy
    term:
      id: MAXO:0000058
      label: pharmacotherapy
    qualifiers:
    - predicate:
        preferred_term: therapeutic procedure
        term:
          id: NCIT:C49236
          label: Therapeutic Procedure
      value:
        preferred_term: phototherapy
        term:
          id: NCIT:C15301
          label: Phototherapy
    - predicate:
        preferred_term: specify therapeutic agent
        term:
          id: NCIT:C157096
          label: Specify Therapeutic Agent
      value:
        preferred_term: clobetasol
        term:
          id: NCIT:C65339
          label: Clobetasol
  evidence:
  - reference: PMID:1671328
    reference_title: "Human immunodeficiency virus-associated eosinophilic folliculitis. A unique dermatosis associated with advanced human immunodeficiency virus infection."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A clinical response was noted to astemizole, to ultraviolet light in the B range, and to topical clobetasol propionate."
    explanation: Supports specific adjunctive therapies in eosinophilic folliculitis context.
transmission:
- name: Waterborne exposure in contaminated hot-tub settings
  description: Outbreak-associated folliculitis can follow exposure to contaminated spa water.
  effect: Causes clustered Pseudomonas folliculitis cases after shared exposure
  evidence:
  - reference: PMID:6402527
    reference_title: "Hot tub dermatitis: a familial outbreak of Pseudomonas folliculitis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A family of three and a neighbor developed Pseudomonas folliculitis after using a home hot tub from which P. aeruginosa was cultured."
    explanation: Demonstrates clustered exposure-associated transmission dynamics.
  - reference: PMID:3955486
    reference_title: "Nosocomial outbreak of Pseudomonas aeruginosa folliculitis associated with a physiotherapy pool."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "After hyperchlorination and structural repairs to the pool, no further cases were identified among pool users."
    explanation: Supports contaminated-water transmission by showing outbreak termination after decontamination and source control.
diagnosis:
- name: Cytologic evaluation of follicular lesions
  description: Cytology is a practical first diagnostic step to distinguish infectious causes of folliculitis.
  diagnosis_term:
    preferred_term: diagnostic procedure
    term:
      id: MAXO:0000003
      label: diagnostic procedure
    qualifiers:
    - predicate:
        preferred_term: diagnostic procedure
        term:
          id: NCIT:C18020
          label: Diagnostic Procedure
      value:
        preferred_term: cytology
        term:
          id: NCIT:C16491
          label: Cytology
  evidence:
  - reference: PMID:22639852
    reference_title: "First step in the differential diagnosis of folliculitis: cytology."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cytology, a simple, rapid, inexpensive, and repeatable diagnostic method, can reveal various bacterial, fungal, viral, and parasitic pathogens."
    explanation: Supports cytology as a first-line etiologic diagnostic method.
- name: Direct microscopy for Malassezia folliculitis
  description: Diagnostic confirmation can include quantification of yeast forms in follicular samples.
  diagnosis_term:
    preferred_term: diagnostic procedure
    term:
      id: MAXO:0000003
      label: diagnostic procedure
    qualifiers:
    - predicate:
        preferred_term: diagnostic procedure
        term:
          id: NCIT:C18020
          label: Diagnostic Procedure
      value:
        preferred_term: microscopy
        term:
          id: NCIT:C16853
          label: Microscopy
  evidence:
  - reference: PMID:27581777
    reference_title: "Treatment Outcomes for Malassezia Folliculitis in theDermatology Department of a University Hospital in Japan."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The diagnosis of Malassezia folliculitis was established on the basis of characteristic clinical features and direct microscopic findings (10 or more yeast-like fungi per follicle)."
    explanation: Provides a specific microscopy-based diagnostic threshold.
  - reference: PMID:35249719
    reference_title: "Dermoscopy as an Auxiliary Tool in the Assessment of Malassezia Folliculitis: An Observational Study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Ten percent potassium hydroxide examination is usually performed to confirm the diagnosis."
    explanation: Adds independent support for KOH microscopy as a practical confirmatory diagnostic approach.
- name: Clinical suspicion for acneiform mimics
  description: Persistent monomorphic pruritic acneiform eruptions should trigger evaluation for Malassezia folliculitis.
  diagnosis_term:
    preferred_term: diagnostic procedure
    term:
      id: MAXO:0000003
      label: diagnostic procedure
    qualifiers:
    - predicate:
        preferred_term: diagnostic procedure
        term:
          id: NCIT:C18020
          label: Diagnostic Procedure
      value:
        preferred_term: clinical evaluation
        term:
          id: NCIT:C124351
          label: Clinical Evaluation
  evidence:
  - reference: DOI:10.3390/jof11090662
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A high index of clinical suspicion is critical in patients with recalcitrant acneiform eruptions."
    explanation: Supports a practical diagnostic heuristic to reduce misclassification as acne vulgaris.
- name: Source and pathogen confirmation in hot-tub folliculitis
  description: Culture from suspected exposure sources supports etiologic confirmation in outbreaks.
  diagnosis_term:
    preferred_term: diagnostic procedure
    term:
      id: MAXO:0000003
      label: diagnostic procedure
    qualifiers:
    - predicate:
        preferred_term: diagnostic procedure
        term:
          id: NCIT:C18020
          label: Diagnostic Procedure
      value:
        preferred_term: microbial culture procedure
        term:
          id: NCIT:C25300
          label: Microbial Culture Procedure
  evidence:
  - reference: PMID:6402527
    reference_title: "Hot tub dermatitis: a familial outbreak of Pseudomonas folliculitis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A family of three and a neighbor developed Pseudomonas folliculitis after using a home hot tub from which P. aeruginosa was cultured."
    explanation: Supports microbiological source confirmation during outbreak investigation.
  - reference: PMID:3955486
    reference_title: "Nosocomial outbreak of Pseudomonas aeruginosa folliculitis associated with a physiotherapy pool."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "P. aeruginosa, serotype O:10, was isolated from three physiotherapists, the patient with an infected surgical wound and the pool."
    explanation: Supports diagnostic source tracing by matching patient and environmental isolates during an outbreak.
clinical_trials:
- name: NCT06307223
  phase: PHASE_IV
  status: COMPLETED
  description: >-
    Interventional study evaluating topical 30% supramolecular salicylic acid
    plus active zinc in Malassezia folliculitis, including recurrence-relevant
    follow-up over 12 weeks.
  target_phenotypes:
  - preferred_term: pustule
    term:
      id: HP:0200039
      label: Pustule
  - preferred_term: pruritus
    term:
      id: HP:0000989
      label: Pruritus
  evidence:
  - reference: clinicaltrials:NCT06307223
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In the present study, investigators evaluated the clinical efficacy of topical application of supramolecular salicylic acid in combination with zinc pyrithione for the treatment and prevention of Malassezia folliculitis recurrence."
    explanation: Supports direct trial relevance to Malassezia folliculitis treatment and recurrence prevention.
- name: NCT06818058
  phase: PHASE_II
  status: RECRUITING
  description: >-
    Randomized placebo-controlled multicenter phase II trial of topical
    TAR-0520 gel for prevention of EGFR inhibitor-associated folliculitis in
    metastatic colorectal cancer.
  target_phenotypes:
  - preferred_term: erythematous papule
    term:
      id: HP:0030350
      label: Erythematous papule
  - preferred_term: pustule
    term:
      id: HP:0200039
      label: Pustule
  evidence:
  - reference: clinicaltrials:NCT06818058
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A Phase II, multicentric, randomized, double-blind, placebo-controlled, parallel- group trial to confirm the good safaty profile and to explore the preventive effect of topically applied TAR-0520 gel on folliculitis developed in metastatic colorectal cancer (mCRC) patients treated with monoclonal anti-EGFR antibodies."
    explanation: Supports an ongoing controlled trial focused on prevention of EGFR inhibitor-associated folliculitis.
- name: NCT02157688
  phase: NOT_APPLICABLE
  status: COMPLETED
  description: >-
    Comparative bacteriological study in folliculitis decalvans designed to
    clarify the role of Staphylococcus aureus in disease pathophysiology.
  target_phenotypes:
  - preferred_term: alopecia
    term:
      id: HP:0001596
      label: Alopecia
  - preferred_term: pustule
    term:
      id: HP:0200039
      label: Pustule
  evidence:
  - reference: clinicaltrials:NCT02157688
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The pathophysiology is poorly understood, Staphylococcus aureus (SA) appears to play a role, never previously studied, and the study will attempt to clarify it."
    explanation: Supports trial relevance to microbial mechanisms in folliculitis decalvans, a clinically important folliculitis subtype.
- name: NCT07268534
  phase: PHASE_II
  status: NOT_RECRUITING
  description: >-
    Adaptive phase II/III clinical trial evaluating biologic strategies for
    folliculitis decalvans, motivated by limited durability of antibiotic-only
    treatment and cytokine-pathway hypotheses.
  target_phenotypes:
  - preferred_term: alopecia
    term:
      id: HP:0001596
      label: Alopecia
  - preferred_term: pustule
    term:
      id: HP:0200039
      label: Pustule
  evidence:
  - reference: clinicaltrials:NCT07268534
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Short-term efficacy rate of antibiotics is around 50-60%, but unfortunately, recurrences/relapses are occurring 5 to 7 months on average after stopping antibiotics, requiring their reintroduction/long-term use and potentially less efficacy/ecological harms."
    explanation: Supports unmet-need rationale for intervention trials beyond antibiotics in FD.
  - reference: clinicaltrials:NCT07268534
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "FD is a non-curable disease for which inflammatory pathways involving several cytokines as TNF, IL1β, IL8, TGFβ, IL12 and 23, could also play a role."
    explanation: Supports cytokine-targeted biologic trial rationale in FD.
  notes: ClinicalTrials.gov status is "not yet recruiting"; mapped to schema enum NOT_RECRUITING.
differential_diagnoses:
- name: Acne
  disease_term:
    preferred_term: acne
    term:
      id: MONDO:0011438
      label: acne
  description: Acne and folliculitis both produce papulopustular lesions but differ in comedones and typical distribution patterns.
  distinguishing_features:
  - Acne typically has comedones and facial/truncal sebaceous distribution.
  - Folliculitis often has follicle-centered lesions and may be linked to specific infectious exposures.
  evidence:
  - reference: PMID:12113648
    reference_title: "Pustular skin disorders: diagnosis and treatment."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Localized pustular eruptions are seen on the hands and feet in adults with pustulosis palmaris et plantaris and acrodermatitis continua (both of which may be variants of psoriasis); on the face in patients with acne vulgaris, rosacea, and perioral dermatitis; and on the trunk and/or extremities in patients with folliculitis."
    explanation: The abstract lists acne and folliculitis as overlapping pustular disorders with different common distributions.
- name: Furunculosis
  disease_term:
    preferred_term: furunculosis
    term:
      id: MONDO:0100595
      label: furunculosis
  description: Furunculosis represents deeper suppurative follicular infection than superficial folliculitis.
  distinguishing_features:
  - Furunculosis generally presents as deeper, more painful boils/abscesses.
  - Folliculitis is usually more superficial and papulopustular.
  evidence:
  - reference: DOI:10.1159/000499184
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The most frequent <i>S. aureus</i> infections include impetigo, folliculitis, furuncles, furunculosis, abscesses, hidradenitis suppurativa, and mastitis."
    explanation: Places folliculitis and furunculosis within overlapping staphylococcal skin infection spectrum requiring clinical differentiation.
  - reference: PMID:15482221
    reference_title: "Treatment of staphylococcal scalded skin syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "S. aureus is one of the most common causes of skin infection, giving rise to folliculitis, furunculosis, carbuncles, ecthyma, impetigo, cellulitis and abscesses."
    explanation: Provides additional spectrum-based evidence supporting furunculosis as a key differential within staphylococcal follicular infections.
- name: Hidradenitis suppurativa
  disease_term:
    preferred_term: hidradenitis suppurativa
    term:
      id: MONDO:0006559
      label: hidradenitis suppurativa
  description: Hidradenitis has chronic nodules/sinus tracts in intertriginous sites and can mimic recurrent follicular infection.
  distinguishing_features:
  - Typical involvement of apocrine/intertriginous regions with sinus tracts and scarring.
  - Folliculitis usually involves superficial follicular papules and pustules without chronic sinus formation.
  evidence:
  - reference: DOI:10.1159/000499184
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The most frequent <i>S. aureus</i> infections include impetigo, folliculitis, furuncles, furunculosis, abscesses, hidradenitis suppurativa, and mastitis."
    explanation: Supports hidradenitis suppurativa as a clinically overlapping condition in staphylococcal-spectrum skin disease discussions.
datasets:
- accession: geo:GSE301280
  title: Spatial transcriptomics reveals dysfunctional lipid metabolism and abnormal pilosebaceous differentiation in acne vulgaris
  description: >-
    Spatial transcriptomics dataset in human acne lesions with an associated
    experimental component showing reduced pustule formation in a mouse model of
    high-fat-diet-induced folliculitis.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  data_type: SPATIAL_TRANSCRIPTOMICS
  sample_count: 24
  conditions:
  - healthy skin
  - non-lesional acne skin
  - comedonal acne skin
  - pustular acne skin
  evidence:
  - reference: GEO:GSE301280
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here, we performed spatial transcriptomics on healthy, non-lesional, comedonal, and pustular acne skin using a custom panel targeting sebaceous differentiation, lipid metabolism, and retinoid signaling pathways."
    explanation: Supports this as a human pilosebaceous spatial transcriptomics resource relevant to follicular inflammatory biology.
  - reference: GEO:GSE301280
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Finally, we demonstrate that an AP-1 inhibitor, T-5224, strongly downregulates FABP5 in human keratinocytes and reduces pustule formation in a mouse model of high fat diet-induced folliculitis."
    explanation: The same GEO summary includes a linked mouse folliculitis model result, increasing disease relevance.
  notes: Included as a related pilosebaceous inflammation dataset with explicit folliculitis-model context.
- accession: geo:GSE273571
  title: JAK-STAT1 as therapeutic target for EGFR deficiency-associated inflammation and scarring alopecia (RNA-seq of HFSC)
  description: >-
    Bulk RNA-seq of mouse hair follicle stem cells from EGFR-deficient versus
    wild-type conditions in a model used to study chronic folliculitis and
    scarring alopecia.
  organism:
    preferred_term: house mouse
    term:
      id: NCBITaxon:10090
      label: Mus musculus
  data_type: BULK_RNA_SEQ
  sample_count: 6
  conditions:
  - hair follicle stem cells, EGFR-deficient model
  - hair follicle stem cells, wild type
  publication: PMID:39521937
  evidence:
  - reference: GEO:GSE273571
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Mechanistically, disruption of EGFR signalling generated a cell-intrinsic hypersensitivity within the JAK-STAT1 pathway, which, synergistically with interferon gamma expressing CD8 T-cell and NK-cell-mediated inflammation, compromised the stem cell niche."
    explanation: Supports mechanistic transcriptomic interrogation of EGFR-driven follicular inflammatory injury.
  - reference: GEO:GSE273571
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Our findings offer molecular insights and present a mechanism-based therapeutic strategy for addressing chronic folliculitis associated with EGFR-inhibitor anti-cancer therapy and cicatricial alopecia."
    explanation: Explicitly links this dataset context to chronic folliculitis biology.
- accession: geo:GSE273572
  title: JAK-STAT1 as therapeutic target for EGFR deficiency-associated inflammation and scarring alopecia (scRNA-seq)
  description: >-
    Single-cell RNA-seq of EGFR-deficient mouse epidermal context generated to
    characterize follicular immune-epithelial dysregulation in scarring
    folliculitis biology.
  organism:
    preferred_term: house mouse
    term:
      id: NCBITaxon:10090
      label: Mus musculus
  data_type: SINGLE_CELL_RNA_SEQ
  sample_count: 1
  conditions:
  - EGFR-deficient epidermal context
  publication: PMID:39521937
  evidence:
  - reference: GEO:GSE273572
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In this study, we demonstrated the protective role of hair follicle-specific epidermal growth factor receptor (EGFR) against scarring hair follicle destruction."
    explanation: Supports the dataset's central focus on follicle-protective EGFR signaling in a scarring folliculitis model.
  - reference: GEO:GSE273572
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Notably, a case study of folliculitis decalvans, characterized by progressive hair loss, scaling and perifollicular erythema, demonstrated successful treatment with JAK1/2 inhibition."
    explanation: Provides direct folliculitis decalvans clinical linkage for interpretation of model-derived single-cell signatures.
- accession: geo:GSE119376
  title: Adverse Events of anti-EGFR Therapy are Triggered by Hair Eruption and Commensal Skin Microbiota
  description: >-
    Expression profiling of primary human epidermal keratinocytes under EGFR
    inhibition, describing barrier dysfunction and chronic folliculitis-related
    inflammatory programs.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  data_type: MICROARRAY
  sample_count: 12
  conditions:
  - keratinocytes, EGFR inhibition
  - keratinocytes, control
  evidence:
  - reference: GEO:GSE119376
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "In the absence of EGFR, opening of the follicular ostia during hair eruption allows invasion of commensal microbiota aggravating barrier disruption and initiating an additional Th1 and Th17 response."
    explanation: Supports EGFR-perturbation-associated follicular barrier and immune dysregulation mechanisms.
  - reference: GEO:GSE119376
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Chronic folliculitis leads to Staphylococcus aureus dominated dysbiosis, further exacerbating inflammation and expanding barrier defects."
    explanation: Directly supports chronic folliculitis-associated dysbiosis and inflammatory amplification.