Word: permethrin
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Dates: during 1998-1998
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...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...