Word: permethrin
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...joys of childhood are timeless: Swing sets, birthday parties... the occasional school-wide outbreak of head lice. It used to be that a quick dose of a foul-smelling mixture called permethrin (Nix, Rid) and a fierce comb-through were enough to annihilate the bloodsucking pests and their eggs, but now those days of relative ease may be over. According to the results of a Harvard University study of 75 lice-infested children, some lice are no longer susceptible to over-the-counter medicines traditionally recommended by pediatricians. And so kids who come home with a case of head lice...
...bottle of Kwell, a hot dryer and a good cleaning did the job. But today's louse, a.k.a. Pediculus humanus capitis, which nests in 12 million new heads annually, is a hardier bug, having grown resistant to the prescription drugs lindane and Elimite and the over-the-counter permethrin drug Nix, which remain imperfect mainstays in the treatment of lice. "The pyrethrins [RID, Pronto and A-200 Pyrinate] aren't working as well as they used to either," says University of Miami lice expert Terri Meinking. Such insecticide products all have side effects. And none are 100% ovicidal, which doesn...
...shop in human scalps and lay eggs, or nits, that they cement to hair shafts. Head lice do not carry disease, but they are tenacious and a rather nasty sight. In the past few decades, the problem had been controlled with shampoos or soaps, many of them containing permethrin, the most widely used of the lice-killing chemicals called synthetic pyrethroids. In recent years, however, the frequency of infestations has increased, and ever greater numbers of children are becoming reinfested within days of treatment. All this has led health officials and researchers to begin worrying about the emergence...
Researchers speculate that overexposure to permethrin may have sparked a process of natural selection in lice. A similar use of preventive insecticides encouraged the rise of resistant strains of the mosquitoes and black flies responsible for transmitting malaria and African river blindness. Although no definitive studies on resistant strains of head lice have been completed in the U.S. (results of a Harvard investigation won't be ready for several months), two recent papers from Israel and the Czech Republic seem to support the resistant-strain theory. Says Thomas Bell, health officer for three counties in Washington State...