Demodex folliculorum

Definition

A microscopic parasitic mite (Arachnida: Trombidiformes: Demodecidae) that resides exclusively in human hair follicles, particularly those of the face where sebaceous glands are concentrated. Adults are elongated and worm-like, measuring approximately 0.3–0.4 mm, with short legs clustered near the anterior end. The species is generally regarded as a commensal of humans, but high population densities can trigger inflammatory skin conditions collectively termed demodicosis, including blepharitis of the eyelid margins.

Etymology

Latin Demodex, from Greek dēmos 'fat, tallow' + dēxein 'to bite'; folliculorum, genitive plural of folliculus 'small sac, follicle', referring to its habitat in hair follicles.

Example

In veterinary and medical entomology, D. folliculorum serves as a model for studying host-specific ectoparasite evolution; its congener D. brevis inhabits sebaceous glands rather than follicles, allowing comparative studies of microhabitat specialization within the same host.

Related Terms

• Demodex brevis
• demodicosis
• commensalism
• Ectoparasite
• Trombidiformes
• blepharitis
• sebaceous gland

Usage Notes

Specialists distinguish D. folliculorum from D. brevis by microhabitat (follicle vs. sebaceous gland) and morphological details; the two species are often reported together in human skin biopsies. The term 'folliculorum' is sometimes misspelled 'folliculorum' in older literature; authority is conventionally cited as (Simon, 1842). Population density assessment requires standardized skin-surface biopsy or lash sampling techniques, as casual observation is insufficient for clinical diagnosis.