Foliculitis

Hair follicles serve as a portal for a number of bacteria, though S. aureus is the most common cause of localized folliculitis. Sebaceous glands empty into hair follicles and ducts and, if blocked, form sebaceous cysts, which may resemble staphylococcal abscesses or may become secondarily infected. Infection of sweat glands (hidradenitis suppurativa) can also mimic infection of hair follicles, particularly in the axillae. Chronic folliculitis is uncommon except in acne vulgaris, where constituents of the normal flora (e.g., Propionibacterium acnes) may play a role.

Diffuse folliculitis occurs in two settings. "Hot-tub folliculitis" is caused by Pseudomonas aeruginosa in waters that are insufficiently chlorinated and maintained at temperatures between 37 and 40°C. Infection is usually self-limited, though bacteremia and shock have been reported. Swimmer's itch occurs when a skin surface is exposed to water infested with freshwater avian schistosomes. Warm water temperatures and alkaline pH are suitable for mollusks that serve as intermediate hosts between birds and humans. Free-swimming schistosomal cercariae readily penetrate human hair follicles or pores but quickly die and elicit a brisk allergic reaction causing intense itching and erythema.