Human Demodexmites (Demodex Folliculorumand Demodex Brevis) and Demodicosis

Demodex mites are obligatory human ectoparasites of the hair follicles and sebaceous glands, typically found on face and scalp. They are the largest and most complex organisms of the skin microflora. In humans only two species: Demodex folliculorum and Demodex brevis have been identified. Infestation with Demodex mites is common. In the adult population, these two Demodex species parasitize the normal skin with a prevalence of 20 - 100% and a usual density <5 mites/ cm2. Their potential as causative agents in the pathogenesis of human skin disorders causes continued speculation. Their interaction with the innate and adaptive immune system is unclear. Demodex mites have been found in skin lesions, but disease by Demodex has not been accepted as an entity. There are convincing reports of blepharitis, folliculitis, rosacea-like (rosaceiform) dermatitis, pityriasis folliculorum, Demodex facial dermatitis, perioral / periorbital dermatitis-like demodicosis, Demodex abscesses and scalp folliculitis (human demodectic alopecia) by Demodex, which respond to agents that reduce Demodex numbers. Some lesions similar to rosacea may also be caused by Demodex. All cutaneous diseases caused by Demodex mites are clubbed under the term demodicosis or demodicidosis. Dermatologists have not been able to reach agreement concerning the pathogenetic potential of the mites. The question whether they are mere commensals coincidentally found in diseased skin or a real cause of human skin disorders remains controversial. With growing interest in the microflora of the human skin and its relevance to cutaneous health and disease, the role of this complex organism needs to be better understood.