Folliculitis occurs due to inflammation of the superficial hair follicle, resulting in follicularly centered papules and pustules.

The etiology of folliculitis can be variable, with bacterial, fungal, viral, parasitic, and noninfectious causes reported. A detailed history of comorbid conditions, exposures, and medications, in conjunction with appropriate ancillary testing, can be helpful.

In immunocompetent patients, bacterial folliculitis may be considered, often due to a predisposing factor that allows for increased bacterial burden on the skin surface. Staphylococcus aureus and Streptococcus species are commonly implicated. These predisposing factors include nasal carriage of S. aureus, occlusion, maceration, hyperhydration, complicating pruritic skin diseases, vigorous application of topical medications, shaving, exposure to oils and certain chemicals, and exposure to heated or contaminated water.

In the genital area, in particular, shaving or other methods of hair removal may result in pseudofolliculitis from ingrown hairs or true bacterial folliculitis. Infection may result due to autoinoculation, contamination of tools, normal skin flora, or colonization of the individual performing the procedure. Pustular folliculitis secondary to Candida spp. (see candidiasis) has also been reported in immunocompetent adults, particularly in skin folds. Viral folliculitis secondary to varicella zoster virus, herpes simplex virus, and molluscum contagiosum have been described.

In immunocompromised patients, folliculitis can occur secondary to etiologies similar to those discussed above. For example, bacterial folliculitis may evolve into furunculosis, or inflammation involving deeper aspects of the pilosebaceous unit, in patients with certain risk factors such as diabetes mellitus, immunosuppression, or human immunodeficiency virus (HIV) infection.