Which parasite is known to infest hair follicles and meibomian glands?

• A. Giardia
• B. Sarcoptes scabiei
• C. Pediculus capitis
• D. Demodex

Answer: (D)

Demodex mites are tiny skin residents that live specifically in hair follicles and oil glands. On the eyelids, the two species involved are Demodex folliculorum in the lash follicles and Demodex brevis in the meibomian glands. Their presence is linked to lid inflammation and blepharitis, with signs such as itching, lid margin redness, and the characteristic cylindrical dandruff around the base of the lashes. Diagnosis is often made by inspecting epilated lashes under a microscope to visualize the mites. The other organisms listed don’t inhabit pilosebaceous units: Giardia is a gut parasite, Sarcoptes scabiei makes skin burrows in the epidermis causing scabies, and Pediculus capitis (head lice) lives on hair shafts rather than inside follicles or glands.