Demodex blepharitis is a chronic inflammatory condition of the eyelids caused by an infestation of Demodex mites, primarily Demodex folliculorum and Demodex brevis. These 2 species differ in their preferred sites of colonization: D folliculorum resides at the base of the eyelashes, leading to anterior Demodex blepharitis, while D brevis inhabits the meibomian glands, contributing to posterior Demodex blepharitis.

Demodex mites are the most prevalent microscopic ectoparasites found in human skin. Their infestation rate increases with age, affecting 84% of individuals by age 60 and 100% of those older than 70. Additionally, patients with rosacea tend to harbor greater densities of Demodex mites and have a higher likelihood of developing blepharitis.

The clinical manifestations of inflammation and scaling of the eyelid margins stem from mechanical damage as well as an inflammatory response to mite-associated bacteria and waste products. Symptoms may include itching, burning, or a foreign body sensation.