Head lice are highly contagious. Direct head-to-head contact with an already infested person is the most common way that the spreading of head lice occurs. They may also be spread through contact with infected clothing, combs, or bedding.
Head lice are quite active and can travel quickly, which explains why they are transmitted so easily. But head lice are not long-distance travelers, and they do not do well away from the host. Although adept at moving from hair to hair, they cannot jump or crawl very far (from the floor to someone's head, for example).
(Click Transmission of Head Lice for more information on how head lice is spread. Click Preventing Head Lice to learn about preventing this.)
The three forms of head lice are:
- The egg (also called a nit)
- The nymph
- The adult.
Nits are head lice eggs. They are very small (about the size of a knot in thread), hard to see, and are often confused for dandruff or hairspray droplets. They are oval and usually yellow to white in color. Nits take about one week to hatch. Once hatched, they are white or clear in color.
The nit hatches into a baby head louse, called a nymph. It looks like an adult head louse, but is smaller. To live, the nymph must feed on blood.
The adult louse is about the size of a sesame seed, has six legs, and is tan to grayish-white in color. Adult lice can live up to 30 days on a person's head. To live, adult lice need to feed on blood. If the louse falls off a person, it dies within two days.
Head lice feed about five times a day. To feed, they pierce the skin with their sharp claws, injecting irritating saliva and then sucking the blood that flows out.