DEET Study from Duke University
SOURCE: Environmental News Service, May 10, 2002
DURHAM, North Carolina, May 10, 2002 (ENS) - A common ingredient in mosquito and tick repellents may be linked to some neurological problems, a new study suggests.
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
Mohamed Abou-Donia, PhD has called for further government testing of the chemical's safety in short term and occasional use, particularly in view of Health Canada's recent decision to ban products with more than 30 percent of the chemical.
Every year, about one-third of the U.S. population uses insect repellents containing DEET, available in more than 230 products with concentrations up to 100 percent. While the chemical's risks to humans are still being intensely debated, Abou-Donia says his 30 years of research on pesticides' brain effects indicate the need for caution among the general public.
His numerous studies in rats, two of them published last year, 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. Rats treated with an average human dose of DEET - 40 milligrams per kilogram body weight - performed far worse than control rats when challenged with physical tasks requiring muscle control, strength and coordination.
Such effects are consistent with physical symptoms in humans reported in the medical literature, such as those experienced by some Gulf War veterans, said Abou-Donia.
"If used sparingly, infrequently and by itself, DEET may not have negative effects - the literature here isn't clear," Abou-Donia said. "But frequent and heavy use of DEET, especially in combination with other chemicals or medications, could cause brain deficits in vulnerable populations."
Children are at particular risk for subtle brain changes caused by chemicals in the environment, because their skin more readily absorbs them, and chemicals may affect their developing nervous systems, said Abou-Donia.
Preparations like insecticide based lice killing shampoos and insect repellents are assumed to be safe because severe consequences are rare in the medical literature. Yet subtle symptoms, such as muscle weakness, fatigue or memory lapses, might be attributed to other causes in error, Abou-Donia said.
"The take home message is to be safe and cautious when using insecticides," said Abou-Donia. "Never use insect repellents on infants, and be wary of using them on children in general. Never combine insecticides with each other or use them with other medications. Even so simple a drug as an antihistamine could interact with DEET to cause toxic side effects. Don't spray your yard for bugs and then take medications. Until we have more data on potential interactions in humans, safe is better than sorry."