Head lice: Pediculus humanus capitis, parasitic insects found on the heads of people. Head lice are most often found on the scalp behind the ears and near the neckline at the back of the neck. The lice hold onto the hair with hook-like claws at the end of each of their six legs. Head lice are rarely found on the body, eyelashes, or eyebrows. These insects lay their sticky, white eggs on the hair shaft close to the root, while hatched lice stay mostly on the scalp. Head lice infection is very common and easily acquired by coming in close contact with someone who has head lice, infested clothing, or infested belongings. Preschool and elementary school children and their families are most often infested.
Symptoms include a tickling feeling of something moving in the hair, itching caused by an allergic reaction to the bites, irritability, and sores on the head caused by scratching. Although lice are very small, they can be seen be seen on the scalp when they move. The eggs (nits) are easily seen on hair shafts.
Treatment involves a combination of a topical insecticidal medication and manual removal of all nits with a lice comb or the fingers. Both medication and complete nit removal are necessary to prevent reinfestation. All clothing, bedding, and furniture surfaces must also be washed or sprayed with insecticide. Note that 1% lindane solution (brand name: Kwell) contains gamma benzene, which can be toxic to the brain and has been linked to childhood leukemia. For this reason, these medications are no longer generally recommended for treatment for head lice.