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Am Fam Physician. 2003;67(6):1391-1392

A subcommittee for the American Academy of Pediatrics (AAP) has released a statement clarifying issues of diagnosis and treatment of head lice and making recommendations for dealing with it in the school setting. The report was published in the September 2002 issue of Pediatrics.

In the United States, approximately 6 to 12 million children three to 12 years of age have head lice infestations each year. All socioeconomic groups are affected. Head lice are not a health hazard and are not responsible for the spread of any disease. The condition is not a sign of uncleanliness, but it does cause embarrassment and many unnecessary days lost from school and work.

Head Lice Infestation

The female louse lives about three to four weeks and lays approximately 10 eggs, or nits, a day. The eggs are incubated by body heat and hatch in 10 to 14 days. Once the eggs hatch, nymphs grow for about nine to 12 days, mate, and then females lay eggs. If not treated, this cycle may repeat itself every three weeks.

The gold standard for diagnosing head lice is finding a live louse on the head, which can be difficult. The eggs may be easier to see, especially at the nape of the neck or behind the ears, within 1 cm of the scalp.


Pediculicides are the most effective treatment for head lice infestation, according to the AAP. Instructions on proper use of these products should be given carefully. Safety and efficacy should be taken into account.

Permethrin (1%)

Currently, permethrin is the recommended treatment for head lice. It has low mammalian toxicity and does not cause an allergic reaction in patients with plant allergies. It is a cream rinse applied to hair that is first shampooed with a nonconditioning shampoo and towel dried. After 10 minutes, it is rinsed off, but leaves a residue that is designed to kill nymphs emerging from the eggs not killed with the first application. If live lice are seen seven to 10 days later, application should be repeated. Resistance to 1 percent permethrin has been reported, but the prevalence of this is not known.

Pyrethrins Plus Piperonyl Butoxide

Pyrethrins plus piperonyl butoxide are neurotoxic to lice and have extremely low mammalian toxicity. This treatment should be avoided in patients allergic to chrysanthemums. It is a shampoo that is applied to dry hair and rinsed out after 10 minutes. Twenty to 30 percent of the eggs remain viable after treatment. A second treatment is needed seven to 10 days later to kill newly emerged nymphs. Resistance of adult lice to these products has been reported.

Lindane (1%)

Lindane is a shampoo that should be left on for no more than 10 minutes with a second application in seven to 10 days. Resistance has been reported worldwide, and it has low ovicidal activity. It is only available by prescription and should be used cautiously because several cases of seizures in children have been reported.

Malathion (0.5%)

Malathion is a prescription lotion that is applied to the hair, left to air dry, then washed off after eight to 12 hours. It has high ovicidal activity, but should be reapplied if live lice are seen in seven to 10 days. Because of its high alcohol content, it is highly flammable, and there is a risk of severe respiratory depression if it is ingested. Malathion should be used only in cases resistant to other treatments.

Topical corticosteroids and oral antihistamines may be beneficial for relieving inflammation of the skin in response to topical therapeutic agents.

The oral agents sulfamethoxazole-trimethoprim and ivermectin are sometimes used to treat head lice, but they are not currently approved by the U.S. Food and Drug Administration for use as a pediculicide.

Nit Removal

After treatment with a pediculicide, removal of the eggs is not necessary to prevent spreading the infestation. Because none of the pediculicides is 100 percent ovicidal, removal of the eggs after treatment is recommended for aesthetic reasons or to decrease diagnostic confusion. Nit combs and other products are available to ease the process. Vinegar or vinegar-based products that are applied to the hair for three minutes before combing help loosen the nits attached to the hair shaft.

The actual prevalence of resistance is not known. Family physicians must consider several explanations when facing a persistent case of head lice, including misdiagnosis, noncompliance with treatment protocol, reinfestation, lack of ovicidal properties of the treatment product, or resistance to the pediculicide.

According to the AAP, if a case of head lice is identified, all household members should be checked, and only those with live lice or eggs within 1 cm of the scalp should be treated. It is prudent to treat family members who share a bed with the person who is infected and to clean hair care items and bedding belonging to that person.

A child with active head lice has likely had the infestation for a month or more by the time it is discovered and poses little risk to others. The child does not have a resulting health problem and should stay in class but be discouraged from close, direct head contact with others. The child's parents should be notified immediately, and confidentiality should be maintained so the child is not embarrassed. A child should be allowed to return to school after proper treatment and should not miss valuable school time because of head lice.

Head lice screening programs have not had a significant effect on the incidence of head lice in the school setting over time and are not cost effective.

Coverage of guidelines from other organizations does not imply endorsement by AFP or the AAFP.

This series is coordinated by Michael J. Arnold, MD, Assistant Medical Editor.

A collection of Practice Guidelines published in AFP is available at

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