Study Finds that Mosquito Repellent DEET Affects Nervous System

(Beyond Pesticides, August 12, 2009)

A new study examining the effects of the mosquito repellent DEET on insects, mice and human proteins reports that the chemical interferes with a prominent central nervous system enzyme. This effect is magnified when exposure to DEET is combined with exposure to certain other pesticides.

Entitled, “Evidence for inhibition of cholinesterases in insect and mammalian nervous systems by the insect repellent deet,” and published in BioMed Central (BMC) Biology, the study utilized toxicological, biochemical and electrophysiological techniques to show that DEET is not simply a behavior-modifying chemical, but that it also inhibits cholinesterase activity in both insect and mammalian neuronal preparations. The researchers examined DEET’s effects on mosquitoes, cockroach nerves, mouse muscles, and enzymes purified from fruit flies and humans. Applications of DEET slowed or halted the actions of the enzyme acetylcholinesterase. This enzyme is crucial for regulating nerve impulses in both insects and mammals, and once its functions are disrupted, neuromuscular paralysis, leading to death by asphyxiation result. In humans, symptoms include headache, exhaustion and mental confusion together with blurred vision, salivation, chest tightness, and muscle twitching and abdominal cramps.

The study also investigated the consequences of DEET interactions with carbamate insecticides on the cholinergic system, and found that DEET has the capacity to strengthen the toxicity of carbamates, a class of insecticides known to block acetylcholinesterase.

The results are consistent with previous studies, says Mohammed Abou-Donia, PhD, of the Duke University Medical Center in Durham, N.C, who was not involved in the new work. “DEET is a good chemical for protection against insects,” Dr. Abou-Donia says. “But prolonged exposure results in neurological damage, and this is enhanced by other chemicals and medications.”

In light of these recent findings, SC Johnson, manufacturer of a variety of DEET repellent products released a statement claiming that such concerns were “unfounded.” However, this is not the first study that has highlighted the adverse impacts associated with DEET and its use with other pesticides. Several studies done by a team of Duke University researchers suggest that DEET, in conjunction with permethrin-impregnated clothing, may be linked to Gulf War Syndrome.

DEET (N,N-diethyl-meta-toluamide) is commonly used as an insect repellent but its use has become highly controversial. Scientists have raised concerns about the use of DEET and seizures among children, even though the U.S. Environmental Protection Agency (EPA) claims that there is not enough information to implicate DEET with these incidents. DEET is quickly absorbed through the skin and has caused adverse effects including severe skin reactions including large blisters and burning sensations. Laboratory studies have found that DEET can cause neurological damage, including brain damage in children. DEET was originally developed for military use in 1946 and was then registered for use on the general public in 1957. According to the EPA, more than one third of the U.S. population uses DEET-containing products every year.

However, safer alternatives to DEET include citronella and other essential oils, like oil of lemon eucalyptus which has been recommended as an efficacious alternative by the Center for Disease Control and prevention (CDC). For more information on safer methods to protect yourself from mosquitoes and other insects, please visit Beyond Pesticides’ fact sheet on mosquito repellents.

Source: U.S. News & World Report.