Demodex mites: facts and controversies.

Because Demodex mites are ubiquitous, their potential as human pathogens has often been ignored. This contribution focuses on the growing body of evidence linking Demodex mites with various skin disorders. Histologically, spongiosis and lymphoid inflammation are regularly seen in follicles containing Demodex mites. In animals, they are well established as a cause of mange, and a human counterpart-demodectic alopecia-appears to exist. There is also a statistical association between Demodex mite density and rosacea, facial itching, and chronic blepharitis. Papulovesicular rosacealike lesions and spiny blepharitis often respond to agents that reduce Demodex numbers. Although these observations are not sufficient to fulfill Koch's postulates, Koch's postulates are also not fulfilled for the association between brown recluse spiders and dermal necrosis or the association between streptococci and guttate psoriasis. The evidence linking Demodex mites to human disease has implications regarding treatment.