By studying animals such as chickens and rats, however, researchers are able to compress the time between exposure and the onset of symptoms: 10 months of a rat's life is several years in a human's life. Such overt symptoms are not seen immediately after use but may manifest themselves months or years after exposure, making a cause-and-effect relationship difficult to establish, said Abou-Donia. (Journal of Toxicology and Experimental Health, May, 1996, Volume 48, p. His earlier research, examining the brain effects of three chemicals used during the Persian Gulf War, clearly demonstrated that chickens exhibited similar signs that the Gulf War veterans complained of upon returning from service. With heavy exposure to DEET and other insecticides, humans may experience memory loss, headache, weakness, fatigue, muscle and joint pain, tremors and shortness of breath, said Abou-Donia. Yet subtle symptoms - such as muscle weakness, fatigue or memory lapses -might be attributed erroneously to other causes, he said. Commonly used preparations like insecticide-based lice-killing shampoos and insect repellents are assumed to be safe because severe consequences are rare in the medical literature. "But frequent and heavy use of DEET, especially in combination with other chemicals or medications, could cause brain deficits in vulnerable populations." Children in particular are at risk for subtle brain changes caused by chemicals in the environment, because their skin more readily absorbs them, and chemicals more potently affect their developing nervous systems, said Abou-Donia. "If used sparingly, infrequently and by itself, DEET may not have negative effects - the literature here isn't clear," he said. Such effects are consistent with physical symptoms in humans reported in the medical literature, especially by Persian Gulf War veterans, said Abou-Donia. Moreover, rats treated with an average human dose of DEET (40 mg/kg body weight) performed far worse than control rats when challenged with physical tasks requiring muscle control, strength and coordination. His numerous studies in rats, two of them published last year, clearly demonstrate that frequent and prolonged applications of DEET cause neurons to die in regions of the brain that control muscle movement, learning, memory and concentration. While the chemical's risks to humans are still being intensely debated, Abou-Donia says his 30 years of research on pesticides' brain effects clearly indicate the need for caution among the general public. population uses insect repellents containing DEET, available in more than 230 products with concentrations up to 100 percent. ![]() Every year, approximately one-third of the U.S. has also called for further government testing of the chemical's safety in short-term and occasional use, especially in view of Health Canada's recent decision to ban products with more than 30 percent of the chemical. A Duke University Medical Center pharmacologist is recommending caution when using the insecticide DEET, after his animal studies last year found the chemical causes diffuse brain cell death and behavioral changes in rats after frequent and prolonged use.
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