New research shows that the insect-repelling chemical deet actually functions in the same way as deadly nerve gases and dangerous pesticides, by attacking the nervous systems of both insects and mammals.
“These findings question the safety of deet, particularly in combination with other chemicals,” said researcher Vincent Corbel of Institut de Recherche pour le Developpement in Montpellier.
The chemical known as deet (for N,N-diethyl-meta-toluamide) is found in nearly every commonly used mosquito repellent in the world, and eight billion doses have been applied since its introduction to the consumer market in 1957. The chemical was originally developed as an insect repellent by the U.S. Army in 1946, following experience with jungle warfare in World War II.
Deet’s popularity comes largely from its effectiveness in repelling a variety of medically significant insects over longer periods of time than more natural repellents (such as certain vegetable-based oils), and the fact that it can be incorporated into sprays, liquids or lotions. Yet although researchers have long insisted that the chemical is safe, they still recommend that consumers use the minimum amount of repellent necessary to cover exposed skin or clothing, and that deet repellents not be applied directly to any irritated or injured skin. While the United States allows the sale of 100 percent deet repellents, many other countries limit maximum concentrations of the chemical to 30 or 50 percent.
In spite of the chemical’s long use, researchers are unsure exactly how deet functions to repel mosquitoes. It has long been believed to affect mosquito behavior without harming the insects, probably by interfering with their sense of smell and their ability to find human prey.
Yet the new study, published in the journal BioMed Central Biology, suggests that deet may function by interfering directly with insects’ nervous systems.
“We’ve found that deet is not simply a behavior-modifying chemical but also inhibits the activity of a key central nervous system enzyme, acetylcholinesterase, in both insects and mammals,” the researchers said.
In experiments performed in cockroaches and rats, the researchers found that deet blocked the action of the neurological enzyme acetylcholinesterase. This is the same mechanism that causes the toxic effects of popular carbamate and organophosphate pesticides, as well as chemical weapons such as sarin and VX nerve gas. This may mean that deet repellants are actually insecticides and could damage the human nervous system.
Organophosphates are among the pesticides most commonly implicated in pesticide poisoning worldwide, and are also a commonly used suicide method in agricultural areas. Like nerve gases, organophosphates irreversibly inactivate acetylcholinesterase, leading to excessive salivation and eye watering at low doses, and muscle spasms or death at higher doses. Although carbamates are not as toxic as organophosphates, their effects can be just as severe at high enough doses.
Strong evidence also links these pesticides to dangerous health effects caused by long-term exposure even at low doses.
Previous studies have implicated deet in causing seizures in children, but the current study is the first to uncover how the chemical acts directly on the nervous system.
The researchers also found that the effects of deet were enhanced when it was used in combination with organophosphates or carbamates, as in mixed repellent-insecticide products.
Bahie Abou-Donia of the Duke University Medical Center said that the new findings are consistent with previous research into the risks of deet.
“Deet is a good chemical for protection against insects,” Abou-Donia said. “But prolonged exposure results in neurological damage, and this is enhanced by other chemicals and medications.”
The researchers in the new study suggested that pregnant women and children under the age of six avoid using deet-containing mosquito repellents. Abou-Donia went farther, calling for such products to carry warning labels about deet’s potential to cause neurological harm.
The Environmental Protection Agency has a review of deet’s safety planned for 2012.