The Hazards of DEET
Update Spring 2003
Many people’s response to fears about West Nile Virus (WNV) and the normal annoyance of mosquito bites is to slather on the insect repellent, especially on their children. The most common choice is a DEET based repellent. A study released last summer showed some DEET based products to be the most effective, in that they lasted longer than other products. But DEET based repellents aren’t just hazardous to mosquitoes. From a human health point of view, when mosquito bites are more of a nuisance than a serious health threat, choosing a botanical based repellent makes more sense.
DEET is a registered pesticide. DEET is short for N,N-diethyl-m-toluamide (also known as N,N-diethyl-3-methylbenzamide). It is a member of the toluene chemical family. Toluene is an organic solvent used in rubber and plastic cements and paint removers. DEET is absorbed through the skin and passes into the blood. The Medical Sciences Bulletin, published by Pharmaceutical Information Associates Ltd. reports, “Up to 56% of DEET applied topically penetrates intact human skin and 17% is absorbed into the bloodstream.” Blood concentrations of about 3 mg per litre have been reported several hours after DEET repellent was applied to skin in the prescribed fashion. DEET is also absorbed by the gut.
The most serious concerns about DEET are its effects on the central nervous system. Dr. Mohammed Abou-Donia of Duke University studied lab animals’ performance of neuro-behavioural tasks requiring muscle co-ordination. He found that lab animals exposed to the equivalent of average human doses of DEET performed far worse than untreated animals. Abou-Donia also found that combined exposure to DEET and permethrin, a mosquito spray ingredient, can lead to motor deficits and learning and memory dysfunction.
An emergency medicine bulletin notes that DEET may have significantly greater toxicity when combined with ethyl and isopropyl alcohols and freon which are components of some DEET repellents. In 1998, the US EPA made it illegal for any product containing DEET to make any child safety claims. Products with DEET are required to carry instructions that they should not be used at all for children under 6 months. Additional required warnings state that for children 6 months to 2 years, only concentrations of less than 10% DEET should be used, and only once a day. For children from 2 -12 years old, only concentrations under 10% should be used, and repellents should not be applied more than 3 times a day.
For adults, Health Canada has now banned products with DEET concentrations over 30%, citing health risks and evidence that increasing the percentage does not do much more to repel insects. Health Canada has also banned two in one products which combine sunscreen and DEET, saying they create the potential for people be exposed to too much DEET. The ban does not take effect until December 2004, so consumers may want to be careful not to pick up combination products still on store shelves.
Products containing DEET are now required to carry labels which specify:
- Do not apply over cuts, wounds, or irritated skin.
- Do not apply to hands or near eyes and mouth of young children.
- Do not allow young children to apply this product.
- After returning indoors, wash treated skin with soap and water.
- Do not use under clothing.
- Do not spray in enclosed areas.
Experts recommend that if using DEET, its best to wear long sleeves and long pants, when possible, and apply repellent to clothing rather than skin to reduce exposure. They state DEET based products should only be applied sparingly; saturation does not increase efficiency. DEET repellents should not be inhaled. Repellent-treated clothes should be washed, or kept outside living areas to reduce exposure. Following all these precautions reduces risk, but does not eliminate it.