Head lice are parasitic wingless insects. They live on people's heads and feed on their blood. An adult louse is about the size of a sesame seed. The eggs, called nits, are even smaller - about the size of a knot in thread. Lice and nits are found on or near the scalp, most often at the neckline and behind the ears.
Lice spread by close person-to-person contact. It is possible, but not common, to get lice by sharing personal belongings such as hats or hairbrushes. Children ages 3-11 and their families get head lice most often. Personal hygiene has nothing to do with getting head lice. Head lice do not spread disease.
Treatment is recommended for people who have an active infestation of head lice. All household members and other close contacts should be checked and treated if necessary. Some experts also recommend treating anyone who shares a bed with an infested person. It is important to treat everyone at the same time.
Centers for Disease Control and Prevention