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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.

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