Comb over chemicals: tool may rid heads of pesticideproof lice.

When used systematically for 2 weeks, special combs may be more effective than a single, one-day application of an insecticidal shampoo at ridding a child's scalp of head lice.

In some countries, including the United States and England, many lice have become resistant to pesticide treatments such as permethrin and malathion in lice shampoos (SN: 9/25/99, p. 207). One alternative is to remove the insects with a comb, says medical entomologist Nigel Hill of the London School of Hygiene and Tropical Medicine.

Fine-toothed metal combs are often used to remove lice eggs from hairs, to which the eggs naturally adhere. But those combs can tug painfully on hair and may not remove hatched lice that stay close to the scalp, Hill says. By contrast, plastic "detector" combs have slightly more space between their teeth and are designed primarily to test for an infestation by probing all the way to the scalp, he explains.

To see whether repetitive use of a detector comb could eliminate lice, Hill and his colleagues recruited the families of 133 children in England and Scotland who were diagnosed with lice infestations. One group of families received either of two commercial pesticide treatments, and another group got kits, branded Bug Buster, containing detector combs.

The pesticide products instructed users to apply a single treatment to a person with lice. The kit told users to wet the hair, apply conditioner, comb thoroughly, and repeat the treatment every 4th day over 13 days. In theory, by the end of that period, all viable eggs would have hatched and all lice would have been removed before they reproduced.

In the trial, 57 percent of the children treated by combing were free of lice after 15 days. Only 13 percent of those treated with a pesticide were free of the insects 5 days after the application, the researchers report in the Aug. 13 BMJ, a medical journal.

Bug Buster is produced and sold online by Community Hygiene Concern, a nonprofit group in London that helped Hill's team obtain a research grant from a fund controlled by the British government. "My gut feeling is that any good detector comb will be able to cure lice in the same manner," Hill says.

The study confirms that, "in the right hands, [Bug Buster] seems to be very effective," says family physician Martin Dawes of McGill University in Montreal in an editorial in the journal.

However, Dawes expresses doubts about the apparent degree of difference between the treatments' performance. Participating physicians and nurses knew which patient got which treatment, a factor that might have biased their reporting of the results. Also, he notes, some pharmacists argue that two pesticide applications are needed to effectively treat head lice.