Folliculitis

Overview

Folliculitis is inflammation of the hair follicle - the lesion is always follicle-centred (hair shaft passes through each papule/pustule). Most UK cases are caused by Staphylococcus aureus.

Presentation

•Follicle-centred erythematous papules and pustules - hair shaft visible through lesion

•Pruritus common; may spread with scratching

•Sites - axillae, beard area, scalp, thighs, inguinal regions, trunk (Malassezia)

•Sycosis barbae - deep folliculitis of beard area (S. aureus); risks scarring

•Pseudofolliculitis barbae - NOT infective; curved hairs re-entering skin after shaving; foreign body reaction; does not respond to antibiotics

Investigations

•Clinical diagnosis in most cases - no investigation required

•Skin swab MC&S - recurrent, treatment-resistant, or widespread bacterial folliculitis

•KOH scraping / fungal culture - if Malassezia folliculitis suspected (budding yeast and hyphae)

•HIV test - consider in eosinophilic folliculitis or recurrent severe cases without obvious cause

•Skin biopsy (gold standard) - suspected eosinophilic folliculitis (eosinophilic infiltrate) or to exclude unusual pathology

Differential Diagnosis

•Acne vulgaris - comedones present; restricted to sebaceous-rich sites; folliculitis lacks comedones

•Rosacea - central face erythema/telangiectasia; no follicle-centred pustules

•Keratosis pilaris - follicular plugging; no pus or erythema

•Contact dermatitis - vesicular/eczematous; not follicle-centred

Management

•General measures - avoid shaving affected area; antibacterial wash (e.g. chlorhexidine/Hibiscrub); avoid occlusive clothing and topical steroids on affected area

•First-line (mild-moderate bacterial): topical fusidic acid 2% three times daily for 5-7 days

•Topical mupirocin 2% - alternative if fusidic acid-resistant (reserve given MRSA decolonisation role)

•Second-line (moderate-severe / deep / treatment failure): oral flucloxacillin 500 mg four times daily for 7 days

•Penicillin allergy: clarithromycin or doxycycline (note: prolonged doxycycline may predispose to gram-negative folliculitis)

Complications

•Furuncle (boil) - deep infection of follicle and subcutaneous tissue; direct progression from deep folliculitis

•Carbuncle - coalescence of multiple furuncles; multiple draining sinuses; typically back of neck

•Permanent alopecia - follicular destruction in deep/recurrent scalp folliculitis (e.g. folliculitis decalvans)

•Cellulitis - spread beyond follicle into surrounding dermis

💡
Recurrent folliculitis should prompt investigation for staphylococcal nasal carriage, diabetes mellitus, or immunosuppression - treating the underlying cause is key to prevention.

Key Variants

Folliculitis variants - cause, clue, and treatment
VariantCauseClinical clueTreatment
Bacterial (staph)Staphylococcus aureusFollicle-centred pustules; beard/axillae/thighsTopical fusidic acid; oral flucloxacillin if severe
Hot tubPseudomonas aeruginosaRash 1-4 days post hot tub; trunk/swimwear areasUsually self-resolves 7-10 days; ciprofloxacin if severe/immunocompromised
MalasseziaMalassezia yeast (overgrowth)Pruritic acneiform rash on trunk (not face); no comedones; fails antibioticsTopical ketoconazole wash or clotrimazole; oral itraconazole if refractory
Gram-negativeKlebsiella/Enterobacter after prolonged antibioticsAround nose/mouth after tetracycline use for acneOral isotretinoin (treatment of choice)
EosinophilicSterile; immune dysregulationIntensely pruritic; HIV (CD4 <200); face, trunk, extremitiesPotent topical corticosteroids; antihistamines; optimise ART

Variant	Cause	Clinical clue	Treatment
Bacterial (staph)	Staphylococcus aureus	Follicle-centred pustules; beard/axillae/thighs	Topical fusidic acid; oral flucloxacillin if severe
Hot tub	Pseudomonas aeruginosa	Rash 1-4 days post hot tub; trunk/swimwear areas	Usually self-resolves 7-10 days; ciprofloxacin if severe/immunocompromised
Malassezia	Malassezia yeast (overgrowth)	Pruritic acneiform rash on trunk (not face); no comedones; fails antibiotics	Topical ketoconazole wash or clotrimazole; oral itraconazole if refractory
Gram-negative	Klebsiella/Enterobacter after prolonged antibiotics	Around nose/mouth after tetracycline use for acne	Oral isotretinoin (treatment of choice)
Eosinophilic	Sterile; immune dysregulation	Intensely pruritic; HIV (CD4 <200); face, trunk, extremities	Potent topical corticosteroids; antihistamines; optimise ART

⚠️
Malassezia folliculitis looks like acne on the trunk in a young adult who has recently used antibiotics - antibiotics make it worse. KOH scraping confirms budding yeast. Treat with antifungals, not antibiotics.