Demodex folliculitis (rosacealike demodicosis or papulopustular demodicosis) is inflammation of the pilosebaceous unit that occurs in the presence of the Demodex mite.

Demodex species are the only parasites considered a normal component of the skin microbiome. While there is no definitive mechanism for the role of the mite in inflammation, it is thought that clinical disease develops when the number of organisms reach a critical threshold, with subsequent dermis infiltration and a vigorous immune reaction. The mite may also be a potential bacterial vector, and the superficial, follicle-based pustules of Demodex folliculitis may be related to infection of the hair follicle.

Clinically, there are facial folliculocentric papules and pustules, although nodulocystic and conglobate (with abscesses) variants have also been described. Crusting may be prominent in long-standing cases. Lesions may be scattered over the face or may be localized to the perioral or periauricular areas. Scalp involvement is rare and is typically seen in males with early-onset baldness: here, perifollicular pustules may be associated with erythema, scales, and hair loss. In immunocompromised individuals (such as patients post-transplant or with human immunodeficiency virus [HIV] disease), involvement may be more widespread. In AIDS, Demodex folliculitis has been reported in the setting of immune reconstitution. An eruption resembling acute graft-versus-host disease has been reported in a few patients who had received hematopoietic stem cell transplants.

While an increase in Demodex mites has been found in some patients with rosacea, a direct causal relationship in these patients has not been established.