What are head lice?

Quick Answer
Head lice are tiny, barely visible insectlike animals (arthropods) that may live on the scalp and causeitching. (The term “lice” is plural; the singular is “louse.”) Head lice may also live in the eyebrows and eyelashes and in beards. Infestations in these areas sometimes are from a related species called pubic lice.
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Definition

Head lice are tiny, barely visible insectlike animals (arthropods) that may live on the scalp and cause itching. (The term “lice” is plural; the singular is “louse.”) Head lice may also live in the eyebrows and eyelashes and in beards. Infestations in these areas sometimes are from a related species called pubic lice.

Causes

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

Risk Factors

Risk factors for head lice include sharing hair-grooming items, hats, and other personal items, and having personal contact with people who may have lice. Children are at higher risk for head lice.

Symptoms

Symptoms for head lice include extreme itchiness, skin breaks and possible infection (caused by scratching), swollen lymph nodes, and bacterial infection (if scratching causes open areas on the scalp). Some persons with head lice do not have symptoms.

Screening and Diagnosis

A doctor will ask about symptoms and medical history and will perform a physical exam that includes looking at the head and scalp for lice and lice eggs (called nits). One should not self-diagnose or self-treat head lice. Some treatments can cause irritation and should be used only by people who have the infestation.

Treatment and Therapy

Treating head lice involves removing eggs and killing lice so that they cannot 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.

Treatment includes applying over-the-counter shampoo containing the insecticide permethrin. One should use medications as directed. Re-treatment at seven to ten days is usually required to kill any lice that hatch from remaining (unremoved) eggs.

Another treatment method is removing lice that are on the eyelashes, which may be difficult. Tweezers can be used to pick them off, and petroleum jelly (such as Vaseline) may be used to coat the eyelashes and kill the lice.

Unless instructed otherwise, one should remove eggs manually with specially designed combs. Eggs stick firmly to hair. Products such as Clear, which loosen the eggs, may assist in removal.

Most cases of head lice can be treated with over-the-counter preparations. However, there is increasing resistance to permethrin and pyrethrin in the United States. Malathion, which is available with a doctor’s prescription, has become a first-line treatment because it kills both the lice and their eggs. In certain cases, a doctor may prescribe lindane, a neurotoxic that carries a U.S. Food and Drug Administration (FDA) warning. Malathion should be prescribed only to persons who are unable to take other medications or who have not responded to them. According to the FDA, lindane rarely causes serious side effects (such as seizure and death). Those especially susceptible are infants, the elderly, children and adults weighing less than 110 pounds, and persons with other skin conditions. Lindane is toxic and should not be overused.

Prevention and Outcomes

Lice are common, especially in children. While no records are kept for accurate counts, some estimates show that as many as ten to fifteen million persons annually develop head lice in the United States. To prevent outbreaks of head lice, one should watch for signs of the disease, such as frequent head scratching. One should not share combs, brushes, hats, or other personal items with people who may have lice, and should avoid close contact with people who may have lice.

All family members should be checked for lice and eggs a minimum of once each week. One should thoroughly wash and dry combs, brushes, hats, clothing, bedding, and stuffed animals in the home, and should vacuum carpeting and car seats. The parents or guardians of children with head lice should notify the child’s school, camp, day-care provider, and friends’ parents.

Bibliography

Ashford, R. W., and W. Crewe. The Parasites of “Homo sapiens”: An Annotated Checklist of the Protozoa, Helminths, and Arthropods for Which We Are Home. 2d ed. New York: Taylor & Francis, 2003.

Centers for Disease Control and Prevention. “Head Lice: Prevention and Control.” Available at http://www.cdc.gov/lice/prevent.html.

Despommier, Dickson D., et al. Parasitic Diseases. 5th ed. New York: Apple Tree, 2006.

Diaz, J. H. “Lice (Pediculosis).” In Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases, edited by Gerald L. Mandell, John E. Bennett, and Raphael Dolin. 7th ed. New York: Churchill Livingstone/Elsevier, 2010.

“Ectoparasites.” In Textbook of Family Medicine, edited by R. E. Rakel et al. 7th ed. Philadelphia: Saunders/Elsevier, 2007.

Goddard, Jerome. Physician’s Guide to Arthropods of Medical Importance. 4th ed. Boca Raton, Fla.: CRC Press, 2003.

Roberts, R. J. “Clinical Practice: Head Lice.” New England Journal of Medicine 347, no. 17 (2002): 1381-1382.

U.S. Food and Drug Administration, Medication Guides. Available at http://www.fda.gov/drugs/drugsafety/ucm085729.htm.