Dermatology · PANCE / PANRE

Folliculitis (Bacterial, Hot Tub, Pseudofolliculitis Barbae)

Inflammation of the hair follicle from infection, irritation, or ingrown hairs; presents as follicular pustules and papules.

Also known as: folliculitis, hot tub folliculitis, Pseudomonas folliculitis, pseudofolliculitis barbae, razor bumps, barber's itch

Overview

Folliculitis is inflammation of the hair follicle, presenting as follicular-based papules, pustules, and erythema. Subtypes are defined by etiology: bacterial (most commonly Staphylococcus aureus), Gram-negative (Pseudomonas, after spa/hot tub exposure), fungal (Pityrosporum or dermatophyte), viral (HSV, molluscum), eosinophilic (HIV-related), and mechanical/irritant such as pseudofolliculitis barbae (PFB) caused by ingrown hairs after close shaving.

Epidemiology

Bacterial folliculitis is one of the most common skin infections. Hot tub folliculitis follows contaminated water exposure (improperly chlorinated whirlpools, pools, water slides) and may produce outbreaks. Pseudofolliculitis barbae predominantly affects men with coarse, curly hair — up to 45-83% of Black men who shave — and is also seen in women shaving the bikini area or face.

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Risk factors

Bacterial: occlusion, moisture, friction, shaving, MRSA colonization, immunosuppression, diabetes, prolonged broad-spectrum antibiotics (Gram-negative folliculitis in acne patients)
Hot tub: 8-48 hours after immersion in inadequately chlorinated hot tub, whirlpool, or pool
Pseudofolliculitis barbae: close shaving (especially against the grain or with a multiblade razor), curly hair, Pseudofolliculitis barbae is a result of mechanical hair re-entry — not infection
Pityrosporum folliculitis: hot/humid climate, oily skin, recent antibiotics, immunosuppression
Eosinophilic folliculitis: HIV with low CD4 count or post–stem cell transplant

Pathophysiology

Bacterial folliculitis: S. aureus colonization → infection of the superficial follicle (Bockhart impetigo) or deeper (sycosis barbae). Hot tub (Pseudomonas aeruginosa) folliculitis: the organism thrives in warm water with disrupted chlorination; biofilms and macerated skin allow follicular invasion. Pseudofolliculitis barbae: after close shaving the cut hair tip retracts below the skin surface or curves and reenters adjacent skin, eliciting a foreign-body inflammatory response without infection. Pityrosporum folliculitis: overgrowth of Malassezia yeasts within follicles.

Clinical presentation

Symptoms

Itchy or mildly painful follicular papules and pustules
Bacterial: scattered pustules with central hair on the beard, scalp, thighs, buttocks, axillae
Hot tub: pruritic erythematous follicular papules and pustules on areas covered by swimsuit 8-48 hours after exposure; often spares face, hands, and feet
Pseudofolliculitis barbae: tender, ingrown-hair–centered papules and pustules along the shaved beard (especially mandibular and submental), bikini line, or axilla, beginning 1-2 days after shaving

Signs / physical exam

Bacterial: erythematous papules and pustules with central hair shafts; possible crusting
Hot tub: 2-10 mm pruritic erythematous papules and pustules distributed in a swimsuit pattern; may have associated low-grade fever and malaise; usually self-limited
Pseudofolliculitis barbae: visible ingrown hair tips within or adjacent to inflamed papules; post-inflammatory hyperpigmentation and scarring with chronicity
Pityrosporum folliculitis: monomorphic itchy follicular papules and small pustules on the upper trunk and shoulders in adolescents and young adults
Eosinophilic folliculitis (HIV): pruritic urticarial follicular papules on the face, scalp, and upper trunk; high peripheral eosinophilia

Classic findings

Pruritic follicular papules and pustules in a swimsuit distribution 1-2 days after hot tub use (Pseudomonas); persistent shaving bumps with ingrown hair tips at the beard line (PFB).

Differential diagnosis

Acne vulgaris — Comedones in addition to papules/pustules, distribution on face, chest, back; not strictly follicular only
Acne keloidalis nuchae — Persistent follicular papules and pustules on the posterior neck/scalp in men with curly hair; progresses to keloidal plaques and scarring alopecia
Hidradenitis suppurativa — Intertriginous areas, painful nodules, sinus tracts, scars; involves apocrine-bearing skin
Scabies — Burrows, intense itch, web spaces and genitals, household contacts; mite on scraping
Eczema or contact dermatitis — Pruritic, scaly patches without follicular pustules; positive patch test
Tinea barbae or capitis — Boggy plaques (kerion) with broken hairs, lymphadenopathy; KOH positive
Insect bites/papular urticaria — Pruritic papules in exposed sites, often clustered, history of exposure

Diagnostic workup

Diagnostic criteria

Clinical diagnosis based on morphology and exposure history. Culture and Gram stain confirm bacterial etiology; KOH confirms fungal causes.

Labs

Usually clinical diagnosis
Bacterial culture and Gram stain of pustule contents when atypical, recurrent, severe, or suspected MRSA
KOH preparation and fungal culture if Pityrosporum, tinea, or dermatophyte suspected
HSV PCR or Tzanck if vesicular morphology
HIV test and CD4 in suspected eosinophilic folliculitis
Pseudomonas culture rarely needed but confirms hot tub folliculitis

Imaging

Not routinely required
Ultrasound or imaging if abscess or deeper soft tissue involvement suspected (furuncle, carbuncle)

Diagnostic algorithm

Subtype	Cause	Classic Distribution	First-line Therapy
Bacterial (Bockhart)	S. aureus (incl. MRSA)	Scattered pustules; beard, scalp, thighs	BPO/chlorhexidine wash; topical or oral anti-Staph antibiotics
Hot tub	Pseudomonas aeruginosa	Swimsuit-covered areas; spares face/hands	Self-limited; ciprofloxacin if severe; remediate water
Pseudofolliculitis barbae	Mechanical (ingrown hairs)	Beard, neck, bikini line	Stop close shaving; topical retinoid; laser hair removal
Pityrosporum	Malassezia yeast	Upper back, shoulders, chest	Ketoconazole shampoo + oral antifungal if severe
Gram-negative	Klebsiella, Proteus, Enterobacter	Face, after long-term tetracyclines for acne	Stop tetracycline; isotretinoin or ampicillin/TMP-SMX
Eosinophilic (HIV)	Unknown; immune-driven	Face, scalp, upper trunk	Antiretrovirals; topical steroids; UVB; itraconazole

Folliculitis subtypes — etiology directs therapy.

Treatment

First-line

Bacterial folliculitis: warm compresses; topical antibacterial wash (chlorhexidine 4%, benzoyl peroxide 5-10%); topical antibiotics (mupirocin 2%, clindamycin 1%) for limited disease
Add oral antibiotics for extensive or recurrent disease: cephalexin 500 mg QID, dicloxacillin 500 mg QID; MRSA suspected → TMP-SMX DS BID, doxycycline 100 mg BID, or clindamycin
Decolonization for recurrent S. aureus folliculitis: intranasal mupirocin BID × 5 days + chlorhexidine washes × 5-14 days; treat household contacts and address fomites
Hot tub (Pseudomonas) folliculitis: usually self-limited (7-14 days); supportive care with cool compresses and topical antipruritics; reserve oral ciprofloxacin 500 mg BID × 7-10 days for severe, persistent, or immunocompromised cases; identify and remediate contaminated water source
Pseudofolliculitis barbae: discontinue close shaving and switch to clipper-only or single-blade shaving in the direction of hair growth; pre-shave preparation with warm water and shaving cream; release ingrown hairs with a sterile needle; topical retinoids (tretinoin 0.025-0.05%) or topical eflornithine 13.9% cream BID to slow hair growth; benzoyl peroxide-clindamycin combination for inflamed lesions

Second-line / adjunct

Recalcitrant pseudofolliculitis barbae: long-pulsed Nd:YAG or diode laser hair removal (safe and effective in skin of color); chemical depilatories cautiously due to irritation
Pityrosporum folliculitis: topical antifungals (ketoconazole 2% shampoo, selenium sulfide, ciclopirox); oral itraconazole or fluconazole for severe or refractory cases
Eosinophilic folliculitis in HIV: antiretroviral therapy is the most effective long-term intervention; symptomatic treatment with topical steroids, oral antihistamines, narrowband UVB, or oral itraconazole
Address recurrent disease: evaluate for diabetes, MRSA carriage, biofilm-laden water sources, occlusive clothing, shared razors

Complications

Bacterial: furuncle (boil), carbuncle, abscess, cellulitis, recurrent MRSA infections
Hot tub folliculitis: rarely otitis externa or systemic Pseudomonas infection in immunocompromised hosts
Pseudofolliculitis barbae: post-inflammatory hyperpigmentation, keloid formation, acne keloidalis nuchae, social and occupational impact (notably for military and uniformed services with strict shaving policies)
Eosinophilic folliculitis: chronic pruritus, scarring
Misdiagnosis as 'recurrent acne' delaying appropriate antimicrobial or behavioral therapy

PANCE pearls

Pruritic follicular papules in a swimsuit pattern 1-2 days after hot tub use = Pseudomonas folliculitis; usually self-limited, no antibiotic needed.
Pseudofolliculitis barbae is a mechanical inflammatory disease — not infection. Stop close shaving rather than chasing antibiotics.
Laser hair removal is the most durable solution for pseudofolliculitis barbae in patients with skin of color when long-pulsed Nd:YAG is used.
Recurrent S. aureus folliculitis warrants decolonization with mupirocin and chlorhexidine, plus addressing household contacts and shared fomites.
Itchy, monomorphic follicular papules on the upper back of an adolescent that 'looks like acne but isn't responding' is often Pityrosporum (Malassezia) folliculitis — treat with topical and oral antifungals, not antibiotics.
Severely pruritic follicular eruption in an HIV patient with low CD4 count is eosinophilic folliculitis; antiretroviral therapy is the key intervention.

References

IDSA SSTI 2014 — Stevens DL et al. Practice guidelines for the diagnosis and management of skin and soft tissue infections (Clin Infect Dis 2014)
AAD review — Ogunbiyi A. Pseudofolliculitis barbae; current treatment options (Clin Cosmet Investig Dermatol 2019)
CDC — CDC. Hot tub rash (Pseudomonas/Folliculitis): healthy swimming guidance (cdc.gov)

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