Infectious Folliculitis

Infectious folliculitis is a common skin condition characterized by the inflammation of hair follicles caused by an infectious agent (bacterial, fungal, viral, or parasitic). Staphylococcus aureus is the most common causative agent. Diagnosis is clinical and presentations include pruritus, follicular pustules, and erythematous papules. Management is usually supportive care but topical or oral antibiotic therapy may be required in severe cases.

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Etiology and Risk Factors

Infectious folliculitis occurs due to inflammation of the superficial or deep portion of the hair follicle caused by an infectious agent (see table below).

Table: Common etiologies, associated risk factors, and examples of pathogens of folliculitis
EtiologyRisk factorsPathogens
Bacterial
  • S. aureus nasal carriers
  • Hyperhidrosis
  • Pruritic skin diseases (e.g., eczema, psoriasis, dermatitis)
  • Long-term use of:
    • Topical corticosteroids
    • Acne antibiotic therapy
  • Shaving against the direction of hair growth
  • Exposure to hot tubs or heated swimming pools
Gram-positive bacteria:
Staphylococcus aureus (most common), both methicillin-sensitive and methicillin-resistant (MRSA) (folliculitis contributes to the increasing prevalence of community-acquired MRSA infections).
Gram-negative bacteria (more common in groin areas):
  • Pseudomonas aeruginosa (“hot tub folliculitis”)
  • Klebsiella
  • Proteus
Fungal
  • Associated with hot, humid climates
  • Immunocompromised status
  • More common in males
  • Increased sweating and sebum production
  • Topical corticosteroid use
  • Immunocompromised status
  • Candida albicans
  • Malassezia species
  • Dermatophytes
Viral
  • Varicella-zoster or herpes virus infection
  • Immunocompromised status
  • Herpes virus
  • Molluscum contagiosum
ParasiticDemodex folliculitisDemodex folliculorum, a parasitic mite

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Clinical Presentation and Diagnosis

Clinical presentation

  • Lesions appear on hair-bearing skin anywhere on the body
  • 2 types of folliculitis: superficial and deep
  • Superficial:
    • Pruritus
    • Follicular pustules
    • Erythematous, tender papules
    • Scarring from prior or recurrent folliculitis eruptions
    • Pseudofolliculitis barbae presents as firm, tender, hyperpigmented papules and pustules, most commonly on the neck and face in men and groin area in women.
  • Deep:
    • Furuncle (“boil”): a purulent nodule arising from folliculitis that affects deeper layers of skin, including subcutaneous tissue
    • Carbuncle: the coalescence of several furuncles into a single mass
    • Furuncles and carbuncles may lead to a skin abscess. 
      • Accumulation of pus and necrotic tissue in the dermis and deeper skin layers
      • Management requires incision and drainage.

Diagnosis

  • Clinical, with no diagnostic tests required
  • However, if the diagnosis is unclear:
    • Gram stain and culture of the pus to identify bacterial pathogen
    • KOH preparation can confirm fungal folliculitis.
    • Viral culture or polymerase chain reaction (PCR) should be used to confirm herpes folliculitis, if suspected.

Management

Management consists mostly of supportive measures:

  • Good skin hygiene
  • Warm compresses
  • Antibacterial soap

Antibiotic therapy is guided by the suspected or known causative organism:

  • Gram-positive bacteria
    • Mild cases: often resolve spontaneously; consider topical mupirocin or topical clindamycin
    • Severe cases: oral antibiotics (cephalexin, dicloxacillin)
    • If MRSA positive, 7–10-day course (occasionally > 2 weeks) of oral trimethoprim/sulfamethoxazole, clindamycin, or doxycycline
  • Gram-negative bacteria
    • Mild cases: often resolve spontaneously
    • Severe cases/immunocompromised patient: oral antibiotics (oral ciprofloxacin or  trimethoprim/sulfamethoxazole)
  • Fungal: requires systemic therapy with oral antifungal agents (itraconazole or fluconazole) 
  • Viral: Herpes infections may require oral acyclovir, famciclovir, or valacyclovir.

Differential Diagnosis

The following conditions can be confused with infectious folliculitis.

Predominantly on face and scalp

  • Acne vulgaris: chronic inflammatory disorder of the pilosebaceous unit that is is self-limiting. Comedones and a lack of pruritus favor acne vulgaris over infectious folliculitis.
  • Rosacea (papulopustular type): inflammatory skin disorder exacerbated by sunlight or alcohol; exhibits pustules, papules, and dilated vessels in an erythematous background
  • Acne keloidalis nuchae: a chronic, scarring folliculitis that primarily affects males of African descent, with papules, pustules, and keloidal nodules on the posterior scalp
  • Pseudofolliculitis barbae (“shaving rash”): inflammation caused by hair penetrating interfollicular skin after shaving (“ingrown hairs”), especially in individuals of African descent; can also occur anywhere hair is shaved or plucked, including axilla, pubic area, and legs 
  • Perioral (periorificial) dermatitis: small erythematous papules around the mouth, nose, or periorbital areas, most commonly in young women
  • Miliaria (“sweat rash”): occurs due to occlusion of eccrine sweat ducts, with extravasation of sweat into dermis causing inflammation; typically seen in body skin folds or areas occluded by clothes or other

Predominantly on trunk or extremities

  • HIV-associated eosinophilic folliculitis: seen in patients with advanced HIV disease, presenting as intense pruritus and recurrent patches of lesions that lead to scarring and hyperpigmentation; uncertain etiology but possibly related to dysregulated immune response to an infectious agent
  • Drug-induced folliculitis: occasionally seen after systemic administration of glucocorticoids, phenytoin, lithium, isoniazid, or cyclosporine
  • Keratosis pilaris: presents with asymptomatic, keratotic follicular papules in children and young adults
  • Prurigo: refers to intensely pruritic papules or nodules (“prurigo nodularis“), often with no known cause. Chronic scratching or rubbing can cause permanent changes to the skin, including hyperkeratosis and hyperpigmentation, and scarring. Associated skin disorders and health conditions include atopic eczema, bullous pemphigoid, allergic reaction to insect bites, iron deficiency, thyroid disease, HIV infection, pregnancy, chronic renal failure, diabetes, and lymphoma.
  • Occupational folliculitis: occurs after chronic exposure to oils (“oil folliculitis”), coal tar, irritants, toxins, or chemicals (e.g., polychlorinated biphenyls [PCBs], dioxins, herbicides). Coal tar is also used therapeutically for eczema and psoriasis.

References

  1. Jackson JD. Infectious folliculitis. Evidence-Based Medicine. UptoDate. Retrieved on August 16, 2020, from https://www.uptodate.com/contents/infectious-folliculitis?search=folliculitis&source=search_result&selectedTitle=1~97&usage_type=default&display_rank=1#H604478874
  2. Oakley A. (2009). Prurigo. DermNet New Zealand (Supported by and contributed to by New Zealand Dermatologists on behalf of the New Zealand Dermatological Society Incorporated). https://dermnetnz.org/topics/prurigo/

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