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Don't Forget to Pack the DEET

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

Article printed on page A9 in the March 17, 2010 issue of
The Mississauga News under the feature: Health & Beauty, Medicine Matters.
Portrait of Dr. Peter W. Kujtan, supplied 2005
Dr. Peter W. Kujtan

March Break is traditionally a time of travel and worry. There may be some confusion about what to take depending on where you are going. Along with the worldwide malaria problem and the hazard of West Nile Virus, has come a new resurgence of interest in mosquito repellents. It's a slam dunk item to take with you.

There is some confusion about the best way to avoid mosquitoes. DEET (N,N-diethyl-3-methylbenzamide) is the most common and 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.

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. DEET is effective in concentrations as low as 5%. The maximum effect can be observed just above the 50% mark.

Most agents that I see in local stores carry a strength of 5-10% and require re-application every couple of hours. It is important to remember that some of what you put on your skin eventually trickles into your system, but 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 than normal and are quite toxic.

Evidence of DEET causing seizures in children with a topical application of 5% concentration is weak. Nevertheless, it has caused a great deal of concern for parents. Children are not more sensitive to the effects of DEET. Similarly, there is little evidence that DEET can damage the unborn fetus, which suggests there is a margin of safety in pregnancy as well. Meanwhile, some people do develop rashes from topical DEET application and most campers learn about its ability to irritate eyes the hard way.

Common sense is perhaps the best approach. Applications should be limited to exposed areas only and should be restricted to either early morning or sunset when mosquitoes are feeding. Products containing DEET are relatively safe in concentrations less than 30%. Used in moderation, it is a sensible way to avoid many insect transmitted diseases both here as well as when travelling in the tropics. Any hesitation to use it could cause worse problems than you know.

Related resources:

How DEET Works by Debra Ronca, from How Stuff Works.
Mosquitoes and West Nile Virus: To Deet or Not To Deet by Nicki Bradley, Moms Editor, BellaOnline: The Voice of Women.
West Nile Virus: FAQ - Insect Repellent Use and Safety from Centers for Disease Control and Prevention (CDC).
DEET Chemistry: What You Need to Know from About.com.
Insect Repellents from Government of Canada. About DEET.
Is DEET Safe to Use? by Francie Diep, Popular Science. Posted June 4, 2014.

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