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Hidradenitis Suppurativa & Follicular Disorders

Name: Hidradenitis Suppurativa & Follicular Disorders
Creator: Veli Bakalov, MD

From plugged follicles to hot-tub pustules: name the cause, pick the fix

Dermatology·Inflammatory Dermatoses·4 min read·9 high-yield points·Reviewed by Veli Bakalov, MD @HemeOncBuddy

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Hidradenitis suppurativa is follicular occlusion and rupture in intertriginous skin, not a primary infection; cultures are often sterile.
Hallmarks: recurrent painful nodules and abscesses, sinus tracts, double-ended comedones and rope-like scars in axillae, groin, inframammary folds and buttocks.
Obesity, smoking and female sex are major risk factors; smoking cessation and weight loss are part of every HS plan.
Hurley I = abscesses without tracts; II = tracts and scars in separated lesions; III = diffuse interconnected tracts.
HS ladder: topical clindamycin → oral tetracyclines or clindamycin-rifampin → adalimumab, secukinumab or bimekizumab; deroof or excise tunnels, because I&D alone recurs.
Biopsy nonhealing areas of long-standing HS for squamous cell carcinoma; watch for anemia and depression.
Hot-tub folliculitis is Pseudomonas under the swimsuit and resolves on its own; itchy monomorphic trunk papules that worsen on antibiotics are Malassezia.
Pseudofolliculitis barbae is a foreign-body reaction to ingrown curly hairs; stop close shaving.
Folliculitis deepens to a furuncle, and coalescing furuncles form a carbuncle; drain them and cover MRSA when systemic signs are present.

Hidradenitis suppurativa: mechanism and presentation

Disease concept. Hidradenitis suppurativa (HS, acne inversa) is a chronic inflammatory disease of hair follicles in intertriginous skin. Infundibular hyperkeratosis plugs the follicle, which dilates and ruptures, spilling keratin and bacteria into the dermis and provoking inflammation driven by TNF-α and IL-17. Bacteria are secondary players, so cultures of lesions are often sterile or grow only skin flora. Onset follows puberty, usually in the 20s.

Clinical picture. Recurrent, deep, painful nodules and abscesses appear in the axillae, groin, inframammary folds, perineum and buttocks. Over time they connect into sinus tracts (tunnels) that drain malodorous discharge and heal with rope-like scars. Double-ended (bridged) comedones are a hallmark. The diagnosis is clinical, resting on typical lesions, typical sites and recurrence; many patients spend years being treated for "recurrent boils" in the same folds.

Risk factors and associations. Obesity, smoking (the strongest modifiable factor), female sex (about 3:1), family history and friction. HS travels with metabolic syndrome, Crohn disease, spondyloarthritis, PCOS, depression and pyoderma gangrenosum, and belongs to the follicular occlusion tetrad with acne conglobata, dissecting cellulitis of the scalp and pilonidal disease.

Staging and treatment

Hurley staging

Stage	Findings	Main approach
Hurley I	Abscesses without sinus tracts or scarring	Topical clindamycin, intralesional steroid, lifestyle
Hurley II	Recurrent abscesses with tracts and scarring; single or widely separated lesions	Oral tetracyclines; deroofing of recurrent tracts
Hurley III	Diffuse or near-diffuse interconnected tracts and abscesses across a region	Biologic therapy plus wide excision

Every patientSmoking cessation, weight loss, loose clothing, chlorhexidine or benzoyl peroxide washes, pain control and screening for depression.
Mild diseaseTopical clindamycin 1%; intralesional triamcinolone rapidly settles a single inflamed nodule.
Moderate diseaseOral doxycycline or minocycline for about 12 weeks; clindamycin plus rifampin is an alternative. Spironolactone or metformin can help selected patients.
Moderate–severe, antibiotic-refractoryAdalimumab (anti-TNF-α), or the IL-17 inhibitors secukinumab or bimekizumab, after screening for tuberculosis and hepatitis B.
Established tunnelsDeroofing removes the roof of a tract and lets the floor heal by secondary intention (Hurley II); wide local excision treats extensive Hurley III disease. Medical therapy continues to limit new lesions.

Incision and drainage relieves an acutely painful, fluctuant abscess but leaves the tract behind, so the lesion returns in the same place. Isotretinoin, so useful in acne vulgaris, works poorly in HS.

Complications. Decades of disease, especially gluteal and perineal HS in men who smoke, can give rise to aggressive squamous cell carcinoma, so biopsy any nonhealing, bleeding or exophytic area. Chronic inflammation also causes anemia and, rarely, AA amyloidosis. Fistulas, genital lymphedema and depression with an increased suicide risk round out the burden.

Folliculitis and its relatives

Folliculitis. Superficial inflammation of hair follicles produces papules and pustules, each centered on a hair, on hair-bearing skin. The setting, itch and distribution point to the cause.

Causes of follicular pustules

Cause	Setting	Lesions	Treatment
Staphylococcus aureus	Shaving, occlusion, sweating, nasal carriage	Tender pustules on beard, thighs, buttocks	Warm compresses; topical mupirocin or clindamycin
Pseudomonas aeruginosa	1–2 days after a poorly chlorinated hot tub, whirlpool or pool	Itchy or tender pustules under the swimsuit; ± otitis externa, malaise	Self-limited in 1–2 weeks; avoid the source; ciprofloxacin only if immunocompromised or severe
Malassezia	Heat, sweat, occlusion, antibiotics, immunosuppression	Intensely itchy, uniform 1–2 mm papules on upper back, chest, shoulders; no comedones	Ketoconazole or selenium sulfide washes; oral fluconazole or itraconazole if extensive
Pseudofolliculitis barbae	Close shaving of tightly curled hair	Papules, pustules, hyperpigmentation, keloidal scars in the beard area	Stop close shaving; laser hair removal, retinoids, low-potency steroids

Malassezia folliculitis. KOH shows round budding yeast. Suspect it whenever "truncal acne" itches, lacks comedones and worsens on antibiotics.

Pseudofolliculitis barbae. Not a primary infection: shaved curly hairs curve back and pierce the skin, provoking a foreign-body reaction, most often in Black men. Growing a beard or using clippers is definitive. If shaving is unavoidable, use a single-blade razor, shave with the grain without stretching the skin, and leave short stubble.

Furuncles and carbuncles. When S. aureus infection extends deeper, a single follicle forms a painful abscess, the furuncle (boil). Coalescing furuncles create a carbuncle, a multiloculated abscess with several draining openings, typically on the nape or upper back and often with fever, especially in people with diabetes. Small furuncles respond to warm compresses; larger furuncles and carbuncles need incision and drainage, with MRSA-active antibiotics (TMP-SMX, doxycycline or clindamycin) for systemic signs or extensive disease. Recurrent furunculosis calls for decolonization with intranasal mupirocin and chlorhexidine washes.