What are head lice?

Also called Pediculus humanus capitis (peh-DICK-you-lus HUE-man-us CAP-ih-TUS), head lice are parasitic insects found on the heads of people. Having head lice is very common. However, there are no reliable data on how many people get head lice in the United States each year.
Who is at risk for getting head lice?

Anyone who comes in close contact with someone who already has head lice, contaminated clothing, and other belongings. Preschool and elementary-age children, 3-10, and their families
are infested most often. Girls get head lice more often than boys, women more than men. In the United States, African-Americans rarely get head lice.

What do head lice look like?

There are three forms of lice: the nit, the nymph, and the adult.

Nit: Nits are head lice eggs. They are hard to see and are often confused for dandruff or hair spray droplets. Nits are found firmly attached to the hair shaft. They are oval and usually yellow
to white. Nits take about 1 week to hatch.

Nymph: The nit hatches into a baby louse called a nymph. It looks like an adult head louse, but is smaller. Nymphs mature into adults about 7 days after hatching. To live, the nymph must
feed on blood.

Adult: The adult louse is about the size of a sesame seed, has six legs, and is tan to greyish-white. In persons with dark hair, the adult louse will look darker. Females lay nits; they are usually larger than males. 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 2 days.

Where are head lice most commonly found?

On the scalp behind the ears and near the neckline at the back of the neck. Head lice hold on to hair with hook-like claws found at the end of each of their six legs. Head lice are rarely found on
the body, eyelashes, or eyebrows.
What are the signs and symptoms of head lice infestation?

* Tickling feeling of something moving in the hair.
* Itching, caused by the an allergic reaction to the bites.
* Irritability.
* Sores on the head caused by scratching. These sores can sometimes become infected.

How did my child get head lice?

* By contact with an already infested person. Contact is common during play at school and at home (slumber parties, sports activities, at camp, on a playground).
* By wearing infested clothing, such as hats, scarves, coats, sports uniforms, or hair ribbons.
* By using infested combs, brushes, or towels.
* By lying on a bed, couch, pillow, carpet, or stuffed animal that has recently been in contact with an infested person.

How is head lice infestation diagnosed?

By looking closely through the hair and scalp for nits, nymphs, or adults. Finding a nymph or adult may be difficult; there are usually few of them and they can move quickly from searching
fingers. If crawling lice are not seen, finding nits within a 1/4 inch of the scalp confirms that a person is infested and should be treated. If you only find nits more than 1/4 inch from the scalp, the infestation is probably an old one and does not need to be treated. If you are not sure if a person has head lice, the diagnosis should be made by a health care provider, school nurse, or a professional from the local health department or agricultural extension service.

This fact sheet is for information only and is not meant to be used for self-diagnosis or as a substitute for consultation with a health care provider. If you have any questions about the disease described above or think that you may have a parasitic infection, consult a health care provider.

© 2003