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 easiest to detect at the neckline and behind the ears.
Head lice are extremely contagious. Close contact or sharing personal belongings, such as hats or hairbrushes, puts people at risk. 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 for head lice is recommended for people with an active infestation. All household members and other close contacts should be checked. Anyone who has an active infestation should be treated. All infested people and their bedmates should be treated at the same time.
Centers for Disease Control and Prevention