Head Lice Fact Sheet
Overview:
The head louse is a parasitic insect that can be found on the head, eyebrows and eyelashes of people. Head lice feed on human blood several times a day and live close to the human scalp.
Three forms of the head louse:
Egg/Nit- Nits are eggs laid by the adult female head louse at the base of the hair shaft nearest the scalp. Nits are firmly attached to the hair shaft and are oval-shaped and very small (about the size of a knot in thread) and hard to see. Nits often appear yellow or white although live nits sometimes appear to be the same color as the hair of the infested person. Nits are often confused with dandruff, scabs or hair spray droplets. Head lice nits usually take about eight to nine days to hatch. Eggs that are likely to hatch are usually located no more than 1/4 inch from the base of the hair shaft. Nits located further than 1/4 inch from the base of hair may very well be already hatched, non-viable nits, or empty nits. This is difficult to determine with the naked eye.
Nymph- A nymph is an immature louse that hatches from the nit. A nymph looks like an adult louse but is smaller. To live, a nymph must feed on blood. Nymphs mature into adults about nine to 12 days after hatching.
Adult- The fully grown and developed 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 look darker in persons with dark hair than in persons with light hair. To survive, adult head lice feed on blood. An adult louse can live about 30 days on a person's head but will die within one or two days if it falls off the person. Adult female head lice are usually larger than males and can lay about six eggs each day.
Signs and Symptoms:
Head lice and their nits are found almost always on the scalp, especially around and behind the ears and near the neckline at the back of the head. Head lice or their nits are sometimes found on the eyelashes or eyebrows but this is uncommon. Head lice hold tightly to hair with hook-like claws at the end of each of their six legs. Nits are cemented firmly to the hair shaft and can be difficult to remove even after hatched.
The signs and symptoms of head lice infestation are:
✔Tickling feeling of something moving in the hair.
✔Itching, caused by an allergic reaction to the bites of the head louse.
✔Irritability and difficulty sleeping due to lice being active in the dark.
✔Sores on the head caused by scratching. These sores can sometimes become infected.
Causes and Transmission:
Head lice move by crawling, they cannot hop or fly. Head lice are spread by direct contact with the hair of an infested person. Anyone who comes in head-to-head contact with someone who already has head lice is at greatest risk. This can happen during play and at sports activities, playgrounds, slumber parties, etc. Personal hygiene or cleanliness in the home or school has nothing to do with getting head lice.
Although uncommon, head lice can be spread by sharing clothing or belongings. This happens when lice crawl, or nits attached to shed hair hatch and get on the shared clothing or belongings. Examples include: Sharing clothing (hats, scarves, coats, sports uniforms) or articles (hair ribbons, barrettes, combs, brushes, towels, stuffed animals) recently worn or used by an infested person and by lying on a bed, couch, pillow or carpet that has recently been in contact with an infested person.
Dogs, cats and other pets do not play a role in the spread of head lice.
Risk Factors:
Head lice are found worldwide. In the United States, infestation with head lice is most common among preschool children attending child care, elementary school children and the household members of infested children, It is estimated that 6 to 12 million infestations occur each year in the United States among children 3 to 11 years of age.
Diagnosis:
Misdiagnosis of head lice infestation is common. The diagnosis of head lice infestation is best made by finding a live nymph or adult louse on the scalp or hair of a person.
Because adult and nymph lice are very small, move quickly and avoid light, they may be difficult to find. Use of a fine toothed louse comb may help in finding live lice.
If crawling lice are not found, finding nits attached firmly within 1/4 inch of the base of the hair shafts suggests, but does not confirm, an infestation. Nits frequently are seen on hair behind the ears and near the back of the neck. Nits that are attached more than 1/4 inch from the base of the hair shaft are almost always already hatched or dead. Head lice and nits can be visible with the naked eye, although use of a magnifying lens may b e necessary to find crawling lice. Nits are often confused with other particles found in hair, such as hair spray droplets, dandruff or dirt particles.
If no nymphs or adults are seen, and the only nits found are more than 1/4 inch from the scalp, then the infestation is probably old and no longer active- and does not need to be treated.
Because adult and nymph lice are very small, move quickly and avoid light, they may be difficult to find. Use of a fine toothed louse comb may help in finding live lice.
If crawling lice are not found, finding nits attached firmly within 1/4 inch of the base of the hair shafts suggests, but does not confirm, an infestation. Nits frequently are seen on hair behind the ears and near the back of the neck. Nits that are attached more than 1/4 inch from the base of the hair shaft are almost always already hatched or dead. Head lice and nits can be visible with the naked eye, although use of a magnifying lens may b e necessary to find crawling lice. Nits are often confused with other particles found in hair, such as hair spray droplets, dandruff or dirt particles.
If no nymphs or adults are seen, and the only nits found are more than 1/4 inch from the scalp, then the infestation is probably old and no longer active- and does not need to be treated.