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Am Fam Physician. 2002;66(6):1065-1066

Despite the lack of any serious medical sequelae, infestation with head lice elicits alarm from affected patients, parents, schools, and society at large. Roberts gives a short review of the current management of head lice.

Infestations are most common during the early grade-school years. Direct head-to-head contact is the mode of transmission. Lice cannot jump or fly, and pets are not vectors.

The adult female louse lays eggs, which hatch after seven days, in sacs (nits) adjacent to the scalp. Any nit that is more than one-quarter inch away from the scalp is an old sac that has migrated up the hair shaft with normal hair growth and is not a sign of active infestation. Adult lice are 3 to 4 mm in length (about the size of a sesame seed).

Visual inspection to confirm infestation is not straightforward. Roberts states that plastic nit combs are just as effective as steel ones and are easier to use. A regular brush or comb is first used to detangle the hair, and then the fine-toothed nit comb is placed at the scalp and drawn through the hair. It usually takes about one minute of combing to find the first louse.

Topical insecticides are a commonly employed treatment. Permethrin and pyrethrin preparations are available over the counter, while malathion and lindane can be obtained only by prescription. For best efficacy, these treatments should be applied to dry hair. The author notes that failure of an over-the-counter pyrethroid preparation indicates that a higher-strength prescription form of the same chemical will likely fail as well, and advises using a different insecticide. The anthelmintic agent ivermectin has been used both orally and topically for head lice but is not licensed for this purpose. Combing alone was found to be only one half as effective as using malathion.

The author reports that some level of resistance has been found for most of the topical insecticides. Permethrin and pyrethrin preparations require a repeat application in seven days and may be less effective than malathion. There are no published trials regarding the efficacy of various herbal remedies available for head lice. Home treatment (e.g., petroleum jelly, mayonnaise, kerosene) also lacks an evidence basis. Head shaving is a drastic and only briefly effective maneuver. Washing all clothes and bedding is probably not necessary, although all combs and brushes should be washed in hot water (or just discarded). Combing should be repeated weekly for several sessions after treatment to ensure successful eradication.

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