Demodex is a genus of tiny parasitic mites that live in or near hair follicles of mammals. About 65 species of Demodex are known; they are among the smallest of arthropods.

Demodex canis lives on the domestic dog. Infestation with Demodex is common and usually does not cause any symptoms, although occasionally some skin diseases can be caused by the mites.

Two species living on humans have been identified: Demodex folliculorum and Demodex brevis, both frequently referred to as eyelash mites. Both species are primarily found in the face, near the nose, the eyelashes and eyebrows, but also occur elsewhere on the body.

In the vast majority of cases, the mites go unobserved, without any adverse symptoms, but in certain cases (usually related to a suppressed immune system, caused by stress or illness) mite populations can dramatically increase, resulting in a condition known as demodicosis or Demodex mite bite, characterised by itching, inflammation and other skin disorders. Blepharitis (inflammation of the eyelids) can also be caused by Demodexmites. There is some evidence linking Demodex mites to some forms of the skin disease rosacea, possibly due to the bacterium Bacillus oleronius found in the mites