The ubiquitous mosquito repellent DEET is indeed extremely effective—at first. A new study finds that the pesky insects are actually able to ignore the chemical over time, reports the BBC. Alarmed by concerns that mosquitoes were developing a resistance to it, British scientists presented some A. aegypti mosquitoes (the kind that spread dengue and yellow fever) with a human arm covered in DEET. At first, the mosquitoes were repelled; but when offered the arm a few hours later, the chemical proved less effective. Sensors on the mosquitoes' antennae showed the insects' sensitivity to DEET diminished over time.
"Mosquitoes are very good at evolving very very quickly," says one researcher, who believes that the insect's olfactory system changes after that first exposure to DEET, which has been the go-to repellent since it was developed by the US military following World War II. Still, he recommends those living in high-risk areas continue to use DEET, and plans future research: to determine exactly how long DEET's effects last after first exposure, and to study its effect on other mosquito species, like those that spread malaria. (In the meantime, keep holding out hope, readers.)
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