DEET Is Your Best Bet for Prevention

By Dr. Peter W. Kujtan, B.Sc., M.D., Ph.D.

Article printed on page 21 in the September 13-14, 2003 issue.
Reprinted on page 12 in the June 5-6, 2004 issue, title: How Safe Is DEET?
Reprinted on page 18 in the August 13-14, 2005 issue of
The Mississauga News under the feature: Health & Wellness, Medical Matters.
Dr K

With the advent of West Nile Virus has come a new resurgence of interest in mosquito repellents. It has been amusing to watch all of the hype and false information spread about the best way to avoid mosquitoes. DEET (chemical name: N,N-diethyl-meta-toluamide) is the commonest and most effective agent known to repel insects that feed on humans. It is the active ingredient in most lotions and spray-on repellents. Initially, it was developed by the US Army at the end of World War II, after the Pacific campaign became bogged down with troops affected by yellow fever, malaria and dengue. DEET is effective in concentrations as low as 5%. Mosquitoes and ticks localize their prey with the help of special receptors on their antennae. DEET is thought to scramble this signal. Effectiveness increases with concentration with the maximum effect observed at just above the 50% mark. Most agents that I see in local stores carry a 5-10% strength, and require re-application every couple of hours. It is important to remember that some of what you put on your skin eventually do trickle into your system. Blood concentrations of DEET resulting from topical application are rarely significant. There have been reports of seizures occurring when DEET solutions have been ingested intentionally or otherwise. These actions result in blood concentrations hundreds of times higher, which are quite toxic. The evidence for 5% topical DEET application causing seizures in children is poor, but none the less has caused a great deal of concern for parents. Children are not more sensitive to the effects of DEET. Similarly, there is little evidence to show that DEET can damage the unborn fetus, suggesting a margin of safety in pregnancy as well. Some people do develop rashes from topical DEET application, and most campers learn the hard way of its ability to irritate the eyes.

Common sense is perhaps the best approach. Applications should be limited to exposed areas only, and restricted to the early morning or sunset times of day when mosquitoes feed. DEET containing products are relatively safe in concentrations less than 30%. Used in moderation, it is a sensible way to prevent many insect transmitted diseases both here and when traveling to the tropics.

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