Head lice are caused by which organism and are found primarily on the scalp and in the hair?

• A. Pediculus humanus corporis; body clothing.
• B. Demodex folliculorum; eyelashes.
• C. Pediculus humans capitis; scalp and hair.
• D. Sarcoptes scabiei; skin mites.

Answer: (C)

Head lice on the scalp are caused by Pediculus humanus capitis, the head louse. These parasites reside on the scalp and in the hair, feeding on small amounts of blood from the scalp. They lay eggs (nits) attached to hair shafts near the scalp, which is why you find them specifically in that area. This distinguishes them from other parasites: the body louse (Pediculus humanus corporis) lives on clothing and only comes to the skin to feed, while Demodex folliculorum is a mite that lives in hair follicles around the eyelashes, and Sarcoptes scabiei is the itch mite that burrows into the skin to cause scabies.