Lice are small, grey, flat, wingless insects that live on the surface of the scalp. An adult louse is 2 mm to 4 mm long.
Lice suck blood from the scalp. They survive by staying close to the scalp for food and shelter. Adult lice lay eggs (nits) that stick to the hair shaft.
Head lice do not indicate poor hygiene. Head lice actually prefer clean hair and skin.
Children with head lice usually have fewer than 20 mature head lice. If they are not treated, lice can live 3 to 4 weeks.
An infestation with lice is also called pediculosis. Audio available.