Folliculitis (plural: folliculitides) is an inflammation of the hair follicle, which is usually infective and due to bacteria, most commonly Staphylococcus aureus. 

Epidemiology

Folliculitis is more common in men ¹.

Risk factors

• shaving
• hot tubs, especially Pseudomonas aeruginosa
• hot climates, especially Malassezia spp.
• fungal folliculitis
  • HIV/immunocompromised

Clinical presentation

Diagnosis is usually clinical with a characteristic appearance of acutely superficially-inflamed hair follicles with small perifollicular papules/pustules with a red base ¹. Occasionally microbiological cultures +/- cytology/histology is required for definitive diagnosis ¹.

Pathology

Folliculitis is an inflammation of the hair follicles.

The related entity, pseudofolliculitis barbae, is a chronic inflammatory response due to shaving ¹.

Etiology

Commonest cause of folliculitis is infection, usually Staphylococcus aureus ¹. Noxious chemicals or trauma much less commonly may cause folliculitis.

• infections
  • bacterial
    • Staphylococcus aureus
    • Streptococcus spp.
    • Pseudomonas aeruginosa: "hot tub folliculitis"
    • Gram-negative folliculitis ⁵, usually chronic antibiotic usage e.g. Escherichia, Klebsiella, Serratia, Proteus, Morganella
  • fungal
    • Malassezia: commonest fungal cause
    • Candida
  • viral
    • herpetic sycosis (usually HSV-1) ⁷
• chemicals
• trauma including shaving, waxing ³, contact sports ⁴
• post-hair transplant: "sterile folliculitis" +/- superinfection ²

Radiographic features

Imaging is not routinely used for the assessment of folliculitis. However, sometimes patients are referred for the soft tissue ultrasound of inflamed skin lesions, and therefore an appreciation of the entity is helpful. Rarely a folliculitis may become complicated by a deeper process e.g. skin abscess.

A study assessed the utility of high-frequency ultrasound for the evaluation of dermatoses of the vulva and showed that lesions such as folliculitis have characteristic appearances ⁶.

Treatment and prognosis

The treatment of folliculitis rests upon antimicrobial therapy.

• bacterial folliculitis
  • initially topical agents, e.g. fusidic acid, benzoyl peroxide, are advised
  • if the response is unsatisfactory then a week's course of oral antibiotics follows, e.g. cephalosporins or flucloxacillin
• pseudomonas folliculitis is usually self-limiting, occasionally an agent such as oral ciprofloxacin might be necessary
• fungal folliculitis: antifungals, e.g. itraconazole, are required
• pseudofolliculitis barbae: commonly settles if shaving of the inflamed area is avoided for ≥4 weeks

Complications

If left untreated or suboptimally-treated then there is a risk of folliculitis progressing to become a furuncle, carbuncle and/or abscess ⁸.

Occasionally, sepsis +/- systemic septic foci (e.g. endocarditis) may result ⁸.