The most common cause of folliculitis is coagulase-positive Staphylococcus aureus, which is a common and normal skin organism in many people (20% to 30% of adults carry S. aureus in their nose). Predisposing factors for folliculitis include an infected wound elsewhere on the body, poor personal hygiene, debilitation, diabetes mellitus, occlusive cosmetics, tight clothes, friction, incorrect shaving technique, exposure to chemicals (cutting oils), and management of skin lesions with tar or with barrier therapy using a steroid. Folliculitis may be caused by bacteria other than S. aureus, such as Propionibacterium, which causes acne.

Untreated furunculosis may lead to cellulitis, which in turn may progress to septicemia if the infection reaches the dermal vascular plexus. Skin lesions are usually uncomplicated, but seeding of the bloodstream can lead to pneumonia, lung abscess, osteomyelitis, sepsis, endocarditis, arthritis, or meningitis. In severe cases, residual permanent scarring may result.

The patient history recounts predisposing factors. The patient may complain of pain, erythema, and edema of several days’ duration.

In patients with folliculitis, inspection usually reveals pustules on the scalp, arms, and legs in children; on the face in bearded men (sycosis barbae); and on the eyelids (styes) in patients of any age.

The degree of hair follicle involvement in patients with bacterial skin infection ranges from superficial folliculitis (erythema and a pustule in a single follicle) to deep folliculitis (extensive follicle involvement) to furunculosis (red, tender nodules that surround follicles with a single draining point) and, finally, to carbunculosis (deep abscesses that involve several follicles with multiple draining points).