Deet losing its effectiveness, study says

Just because you’ve loaded up on Deet doesn’t mean you’re going to be bug free. New research published in the peer-reviewed journal PLOS ONE says the commonly used insect repellent is losing its effectiveness. 

Developed by the U.S. military following WWII, Deet is one of the most widely used mosquito repellants around the world. But despite its widespread and longstanding use, mosquitos appear to be growing resistant to it.  

In order to determine the insect’s response to the chemical, researchers  from the London School of Hygiene and Tropical Medicine repeatedly exposed Aedes aegypti, a species of mosquito that spreads dengue and yellow fever, to arms covered in Deet. The researchers found that while the mosquitos were deterred by the chemical at first, they later ignored it.  

“We found that three hours after pre-exposure the mosquitoes showed behavioural insensitivity,” the researchers wrote. Their findings are consistent with other studies that show mosquitoes can learn to respond differently to odours to maximize feeding success.

“There is something about being exposed to the chemical that first time that changes their olfactory system—changes their sense of smell—and their ability to smell Deet, which makes it less effective,” co-author James Logan told BBC News.

Because mosquitos feed multiple times during their lifespan, the researchers say it is important to study this phenomenon over longer times, “as this would have clear implications for use of repellents for personal protection.” The researchers also hope to also study the effectiveness of Deet in protecting against other mosquitos.