It's Okay To Nit Pick

Some head-scratching new evidence has come to light out of the U.K. via the June 2006 Archives of Disease in Childhood. In a study of 231 school children with head lice, researchers in Wales found that 80 percent of the lice tested had genes that had grown resistant to pyrethroids, synthetic versions of a naturally occurring pesticide found in chrysanthemums and the class of chemicals most commonly used in over-the-counter lice-treatment shampoos and lotions, such as Nix Cream Rinse Lice Treatment.

The study didn't examine pyrethroid resistance in lice in the U.S., but Daniel Kass, director of environmental surveillance and policy for the New York City Department of Health & Mental Hygiene, says he has heard anecdotal evidence that pyrethroid-based lice treatments are losing effectiveness, which amounts to unnecessary chemical exposures if the products aren't working. Permethrin, the most common pyrethroid used in these treatments, is toxic to aquatic life after it's washed down the drain and can cause skin, respiratory and eye irritation in small doses. Even so, Kass says that treatments aren't intended to come in contact with skin long enough to cause any major health effects; most remain on hair for a maximum of 10 minutes and need, at most, two applications to kill the insects. "There is very little data suggesting that a typical and correct treatment—following labels carefully and judiciously—can put kids at risk," says Kass. "These treatments are only dangerous to the extent that lice become more resistant as people use more product," he adds.

While pyrethroid shampoos wash out, pyrethroid home pesticides such as Raid linger in indoor air and can produce ill health effects such as headaches, nausea and, in severe cases, neurological damage, on top of contributing to resistance in pests. So instead, discourage roaches and other insect invaders by using integrated pest management techniques, such as caulking foundation cracks to prevent them from entering and depriving them of food and moisture by sealing food containers and fixing leaks. (See our Pest Control Product reports at www.thegreenguide.com for more ideas).

Another chemical examined in the Welsh study, the organophosphate malathion, was found to be more effective than pyrethroids in killing lice. But that doesn't make it a safer shampoo for humans. Malathion, currently under safety reassessment by the U.S. Environmental Protection Agency, can react with chlorine in water to form malaoxon, a nervous system toxin. Fortunately, its use in head lice treatments in the U.S. is not widespread. The Food and Drug Administration has only approved one malathion-based treatment, a prescription-only product called Ovide Lotion.