Head lice are tiny, barely visible insect-like animals (“arthropods”) that may live on the head and cause itching. ("Lice" is plural; the singular is "louse"). Head lice may also live in the eyebrows, eyelashes, and beard, but sometimes infestations in these areas are from a related species called pubic lice.

Causes

Head lice spread by personal contact and by sharing combs, brushes, hats, and other personal items.

Risk Factors

Anyone who comes in close contact (especially head-to-head contact) with someone who already has head lice is at greatest risk. Occasionally, head lice may be acquired from contact with clothing (such as hats, scarves, coats) or other personal items (such as brushes or towels) that belong to an infested person. Preschool and elementary-age children, 3-11, 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. Personal hygiene or cleanliness in the home or school has nothing to do with getting head lice.

Symptoms

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

Diagnosis

An infestation is 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 (and don't see a nymph or adult louse), 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 your health care provider, school nurse, or a professional from the local health department or agricultural extension service.

Treatment

Treating head lice involves removing eggs and killing lice so that they can't continue to lay eggs. Treatment may be difficult because in some regions lice have become resistant to many of the commonly used medications. Some experts recommend that treatment be given only when live adult lice are seen. They are 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.

Methods include:

• Applying over-the-counter shampoo containing the insecticide, permethrin – It is very important to use medications as directed. Retreatment at 7-10 days is usually required to kill any lice that hatch from unremoved eggs.

• Removing lice on the eyelashes, which may be difficult – Tweezers can be used to pick them off. Vaseline may be used to coat the eyelashes and kill the lice.

• Unless instructed otherwise, removing eggs manually with specially designed combs – Eggs stick firmly to hair. Products such as “Clear," which loosen the eggs, may assist in removal.

In areas with high levels of resistance to permethrin, other prescription medications may be used, including malathion and lindane.

Lindane, a second line treatment, should only be prescribed to patients who are unable to take other medications or who have not responded to them. According to the Food and Drug Administration’s warning, lindane can rarely cause serious side effects, including seizure and death. Those especially susceptible are infants, the elderly, children and adults weighing under 110 lbs, and individuals with other skin conditions. Lindane is toxic and should not be overused. Patients are given small amounts (1-2 oz) of the shampoo or lotion and instructed to apply a very thin layer and not to reapply. For more information, visit the Center for Drug Evaluation and Research website.

Prevention

Lice are common, especially in children. While no records are kept for accurate counts, some estimates are that as many as 10-15 million persons annually develop head lice in the United States. To prevent outbreaks of head lice:

• Watch for signs of head lice, such as frequent head scratching.

• Don't share combs, brushes, hats, or other personal items with people who may have lice.

• Avoid close personal contact with people who may have lice.

• If you or your children have head lice, thoroughly wash and dry combs, brushes, hats, clothing, bedding, and stuffed animals, and vacuum carpeting and car seats.

• If your children get head lice, notify their school, camp, daycare provider, and their friends' parents.

• Check all family members for lice and eggs at least once a week.

RESOURCES

Centers for Disease Control and Prevention
http://www.cdc.gov/

Headlice.org
National Pediculosis Association, Inc.
http://www.headlice.org

CANADIAN RESOURCES

Caring for Kids–Canada
http://www.caringforkids.cps.ca

Communicable Disease Control (CDC) Network
Province of Manitoba
http://www.gov.mb.ca/health/publichealth/cdc/index.html

References:

American Academy of Dermatology website. Available at: http://www.aad.org/default.htm.

Lindane shampoo and lindane lotion. Center for Drug Evaluation and Research. US Food and Drug Administration website. Available at: http://www.fda.gov/cder/drug/infopage/lindane/default.htm. Accessed March 12, 2007.

Medication guide lindane (LIHN-dane) lotion USP, 1%. Center for Drug Evaluation and Research. Food and Drug Administration website. Available at: http://www.fda.gov/cder/drug/infopage/lindane/lindaneLotionGuide.htm. Accessed March 12, 2007.

Medication guide lindane (LIHN-dane) shampoo USP, 1%. Center for Drug Evaluation and Research. Food and Drug Administration website. Available at: http://www.fda.gov/cder/drug/infopage/lindane/lindaneShampooGuide.htm. Accessed March 12, 2007.

National Pediculosis Association, Inc. website. Available at: http://www.headlice.org.

Revised lindane lotion label. Center for Drug Evaluation and Research. Food and Drug Administration website. Available at: http://www.fda.gov/cder/foi/label/2003/006309lotionlbl.pdf. Accessed March 12, 2007.

Revised lindane shampoo label. Center for Drug Evaluation and Research. Food and Drug Administration website. Available at: http://www.fda.gov/cder/foi/label/2003/006309shampoolbl.pdf. Accessed March 12, 2007.

Roberts RJ. Clinical practice. Head lice. N Engl J Med. 2002;346(21):1645-1650.