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Head Lice Infestation
(Pediculosis)
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.
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