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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Question 1DermatologyMedium
A 24-year-old woman presents with an itchy rash that began 2 days ago. She reports soaking in a friend's backyard whirlpool spa for about an hour over the weekend. Examination shows scattered 2-6 mm erythematous papules and pustules, several centered on hair follicles, concentrated over the trunk and buttocks in the area covered by her swimsuit; her face, palms, and soles are spared. She is afebrile and otherwise well. Which of the following is the most likely diagnosis?
AAllergic contact rash
BMiliaria rubra eruption
CMalassezia folliculitis
DHot tub folliculitis
ECercarial dermatitis
Reveal answer & full explanation
Correct answer: D — Hot tub folliculitis
AAllergic contact rash
BMiliaria rubra eruption
CMalassezia folliculitis
DHot tub folliculitis✓
ECercarial dermatitis
Why Hot tub folliculitis is correct
Pseudomonas aeruginosa thrives in warm, inadequately chlorinated whirlpools and invades hair follicles through macerated skin.
The classic picture is pruritic erythematous follicular papules and pustules appearing 8-48 hours (here 2 days) after immersion, distributed in a swimsuit pattern with sparing of the face, palms, and soles.
It is typically self-limited over 7-14 days; oral ciprofloxacin is reserved for severe, persistent, or immunocompromised cases, and the contaminated water source should be remediated.
Why the others are wrong
Allergic contact rash — A pruritic, scaly eczematous eruption limited to the area of allergen contact, without the follicular papules and pustules seen here.
Malassezia folliculitis — Also causes itchy follicular papules and pustules favored by heat, sweating, and occlusion, but it is a monomorphic, subacute-to-chronic eruption of the upper back, chest, and shoulders that often follows antibiotic or corticosteroid use; an abrupt swimsuit-pattern onset within 2 days of whirlpool exposure points to Pseudomonas.
Miliaria rubra eruption — Heat rash from obstructed eccrine sweat ducts produces pruritic, nonfollicular erythematous papules in occluded, sweaty areas; the follicle-centered pustules and the whirlpool exposure favor Pseudomonas folliculitis.
Cercarial dermatitis — swimmer's itch is also an itchy papular eruption after water exposure, but it follows swimming in natural fresh or salt water (lakes, ponds, or ocean) containing avian schistosome cercariae, not soaking in a heated spa, and it affects exposed skin while sparing areas covered by the swimsuit; follicle-centered pustules confined to the swimsuit area after whirlpool use point to Pseudomonas.
Question 2DermatologyMedium
A 26-year-old man presents with tender bumps along his jawline and submental area that flare 1-2 days after he shaves. He has coarse, tightly curled hair and shaves daily against the grain with a multiblade razor. On exam there are firm, erythematous follicular papules and a few pustules, and several inflamed lesions have a hair at their center. There is no honey-colored crust, and the eruption is confined to the shaved beard region. Which of the following best explains the findings?
AKeratin plugging of sebum-rich follicles with Cutibacterium acnes proliferation
BDermatophyte invasion of beard hair follicles producing a deep inflammatory folliculitis
COvergrowth of Malassezia yeast within sebaceous-rich follicles of the beard area
DIngrown hairs re-entering the skin and inciting a foreign-body inflammatory reaction
EStaphylococcus aureus invasion of the superficial follicular opening after shaving
Reveal answer & full explanation
Correct answer: D — Ingrown hairs re-entering the skin and inciting a foreign-body inflammatory reaction
AKeratin plugging of sebum-rich follicles with Cutibacterium acnes proliferation
BDermatophyte invasion of beard hair follicles producing a deep inflammatory folliculitis
COvergrowth of Malassezia yeast within sebaceous-rich follicles of the beard area
DIngrown hairs re-entering the skin and inciting a foreign-body inflammatory reaction✓
EStaphylococcus aureus invasion of the superficial follicular opening after shaving
Why Ingrown hairs re-entering the skin and inciting a foreign-body inflammatory reaction is correct
This is pseudofolliculitis barbae (PFB), a mechanical, not infectious, process. After close shaving, the cut tip of a curly hair retracts below the surface or curves and re-penetrates adjacent skin, eliciting a foreign-body inflammatory reaction.
The clues are classic: coarse curly hair, daily shaving against the grain with a multiblade razor, papules and pustules limited to the shaved beard, and flares within 1-2 days of each shave.
Because it is not an infection, management is behavioral (stop close shaving, shave with the grain or switch to clippers/single-blade, release ingrown hairs) plus topical retinoids; recalcitrant skin-of-color cases respond to long-pulsed Nd:YAG laser hair removal.
Why the others are wrong
Overgrowth of Malassezia yeast within sebaceous-rich follicles of the beard area — This is Pityrosporum (Malassezia) folliculitis: monomorphic, itchy follicular papules and pustules, usually on the upper trunk and shoulders of young adults and often after heat, occlusion, or antibiotics; it is pruritic rather than tender and does not flare with each shave or depend on tightly curled hair.
Staphylococcus aureus invasion of the superficial follicular opening after shaving — This is true bacterial folliculitis (Bockhart impetigo), which produces pustules with central hairs and often honey-colored crust; the absent crust and the pairing of tightly curled hair with close shaving against the grain point to a mechanical cause, not S. aureus.
Dermatophyte invasion of beard hair follicles producing a deep inflammatory folliculitis — This is tinea barbae, usually acquired from farm animals (zoophilic Trichophyton species); it forms a localized, boggy, kerion-like plaque with pustules and loose, easily plucked hairs, is confirmed by KOH or fungal culture, and does not flare within 1-2 days of each shave.
Keratin plugging of sebum-rich follicles with Cutibacterium acnes proliferation — jawline papules and pustules in a young man can suggest acne vulgaris, but acne is built on comedones and does not flare within 1-2 days of each shave or depend on tightly curled hair; inflamed lesions centered on hairs and confined to the shaved beard point to ingrown hairs rather than C. acnes.
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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
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
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
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)
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)
Ogunbiyi 2019 (CCID) — Ogunbiyi A. Pseudofolliculitis barbae; current treatment options (Clin Cosmet Investig Dermatol 2019;12:241-247)
CDC — CDC. Hot tub rash (Pseudomonas/Folliculitis): healthy swimming guidance (cdc.gov)
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