It isn't just nice when mosquito repellents actually do what they claim to—it's necessary. The biting insects are one of nature's top disease vectors, spreading everything from yellow fever and dengue to Zika and malaria, and a group of scientists recently set out to test which of 11 types of repellents actually keep Aedes aegypti mosquitoes at bay. Almost all the products had a small or undetectable effect, including sprays, wearable devices, and citronella candles, reports Science. Only DEET and lemon eucalyptus spray did the trick. To test this, scientists put a person at one end of a wind tunnel to act as the bait, released a band of several dozen hungry mosquitoes, and tried each of the 11 products individually, reports Ars Technica.
Cutter Lemon Eucalyptus, a spray of lemon eucalyptus oil, was apparently so repulsive to the insects that only 29.6% of them dared approach the human; Ben’s Tick & Insect Repellent, a spray-on that is 98% DEET, attracted 33.7% of mosquitoes; and a wearable device, the OFF! Clip-on that fans out metofluthrin insecticide, attracted just 27%. Meanwhile, personal sonic mosquito repellent and citronella candles actually drew more than 90% of the mosquitoes, which was more than the 88% found to venture that way in the control test. "The most egregious danger to the consumer is the false comfort that some repellents give them protection against Ae. aegypti when they actually offer none," the authors write in the Journal of Insect Science. (Mosquito populations are growing in the US.)