​​​What are head lice?

Head lice are small insects that live on the human scalp, feeding on human blood several times a day. These parasites make small bites in the scalp to suck blood and live off of human hosts. The bites do not hurt, but lice excrete a substance to prevent the blood from clotting, which can cause severe itching and allergic reactions. Without a host to feed on, lice will die within 24 hours.

Who gets head lice?

Head lice are found worldwide and can infest any human. In the United States, infestation with head lice is most common among children 3-11 years old. Lice are most often found on children attending child care, preschool, and elementary school. Lice are also often transferred to the household members of infested children. The Centers for Disease Control and Prevention has estimated that up to 12 million children in the U.S. aged three to twelve are infested with head lice each year.

How do lice get into the hair?

  • Head lice move by crawling; they cannot hop or fly.
  • Head-to-head contact with a person who has head lice is the most common way to transfer lice. Head-to-head contact is common during play at school, at home, at the playground, at camp, at slumber parties, and during sports activities.
  • Head lice may also be spread by sharing clothing items. Lice or eggs may have crawled or fallen onto items such as hats, scarves, coats, sports uniforms, helmets, hair ribbons, barrettes, combs, brushes, towels, stuffed animals, pillows, and bedding--to name a few.
  • Head lice may also be spread on furniture and other household items such as beds, couches, chairs, and pillows.
  • Dogs, cats, and other pets do not play a role in the spread of human lice.

Egg / Nit

Lice eggs are laid by the adult female at the base of the hair shaft nearest the scalp. Lice eggs are firmly attached to the hair shaft by a glue-like substance and are oval-shaped, very small (about the size of a knot in thread), and hard to see. Lice eggs often appear yellow or white. Living lice eggs can appear to be the same color as the hair they are on. After hatching, the empty eggshell is called a nit. Lice eggs and nits are often confused with dandruff or other debris. Lice eggs usually take 8–9 days to hatch. Lice eggs that are likely to hatch are usually located less than ¼ inch (5mm) from the base of the hair shaft.


A nymph is a young louse that has recently hatched from a lice egg. A nymph looks like an adult head louse, only smaller. Nymphs, like adult lice, must feed on human blood to survive. Nymphs mature into adult lice 9–12 days after hatching.


A fully-grown adult louse is about the size of a sesame seed, has six legs, and is tan to grayish-white in color. Adult head lice may appear to be the same color as the hair they live in. To survive, they must feed on human blood. Head lice live about 30 days on a person’s head, but will die within 24 hours if they are removed from a food source, such as when they fall off the head. Adult female head lice are usually larger than males and can lay about 8–10 eggs each day.

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