How to mislead a Mosquito

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

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 (N,N-diethyl-3-methylbenzamide) 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 does 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.