Folliculitis

Evidence Levels: A Double-blind study B Clinical trial ≥ 20 subjects C Clinical trial < 20 subjects D Series ≥ 5 subjects E Anecdotal case reports

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Folliculitis is defined as inflammation of the pilosebaceous unit, which can occur superficially, presenting as tender, red papules and pustules, or within the dermal portion of the follicle manifesting as abscesses and furuncles. The etiology of folliculitis can stem from both infectious and non-infectious causes. Among infectious etiologies, bacteria are common, including Gram-positive Streptococcus and Staphylococcus aureus , as well as Gram-negative Pseudomonas infections. Viral etiologies include herpes and molluscum, and fungi and yeast folliculitis can be caused by dermatophytes and Pityrosporum , respectively. Less commonly, parasitic folliculitis may be caused by agents such as Demodex , scabies, and larva migrans.

Non-infectious folliculitis can be caused by mechanical factors such as friction, occlusion, and trauma, including epilation and sunshine. Irritant folliculitis is associated with cutting oils and coal tar, while a history of significant sun exposure can trigger actinic folliculitis. Perforating folliculitis is commonly associated with diabetes mellitus and chronic renal failure. Eosinophilic pustular folliculitis can be seen in infants, immunocompromised or HIV patients, or the rarer Ofuji’s subtype. Many other inflammatory diseases are associated with sterile folliculitis, including Behçet disease, reactive arthritis, systemic lupus erythematosus, rheumatoid arthritis, mixed connective tissue disease, inflammatory bowel disease, lymphoproliferative disease, and pregnancy. There is a growing list of medications that can cause folliculitis including lithium, halogens, corticosteroids (both topically and systemically), androgens, ACTH, isoniazid, phenytoin, and sirolimus. Immune-targeted therapy is a category of medications that cause folliculitis as a side effect, including epidermal growth factor receptor (EGFR) inhibitors, tumor necrosis factor-alpha (TNF-α) inhibitors, trastuzumab, sorafenib, vemurafenib, and dabrafenib.

A thorough history and physical examination are crucial to highlight the most likely etiology in each case. Prolonged antibiotic used in acne patients, particularly tetracycline use, is associated with the development of Gram-negative folliculitis, caused by Pseudomonas and other similar bacteria. Exposure to contaminated pools or Jacuzzis are frequent sources of Pseudomonas folliculitis. Pityrosporum folliculitis is seen commonly in young adults as pruritic perifollicular papules on the upper trunk, often in warm climates or seasons.