Even mosquitoes bred without the ability to sense the smell of deet appear to sense the chemical with their legs when they land on it, and fly away without biting, according to a 2019 study published in the journal Current Biology. But it may be more than just odor at work. Deet may mask the odor of humans, confuse the odor-sensing abilities of mosquitoes, or simply compel them to move away, perhaps because it resembles a natural substance they’ve evolved to avoid. Though scientists found out long ago that deet works, they still don’t know exactly why. Thus N,N-diethyl-meta-toluamide, or deet, was born and eventually registered for use in consumer products in 1957.

A chemical closely related to deet was found to be highly effective, then refined slightly to reduce its tendency to irritate skin. military and the Department of Agriculture jointly screened more than 6,000 different compounds looking for ones that would repel mosquitoes. When scientists are testing the effectiveness of new insect repellent ingredients, they compare them to deet to see how they measure up.ĭeet was discovered in the 1940s essentially by “brute force,” as Matthew DeGennaro, PhD, an associate professor in the department of biological sciences at Florida International University, puts it. It’s “broad spectrum,” meaning it works on a wide variety of bugs, including mosquitoes, ticks, and flies. When it comes to active ingredients that can ward off bugs, it’s hard to beat deet. We’ve also found that some (but again, not all) repellents with 30 percent oil of lemon eucalyptus (OLE) and 20 percent picaridin provide long-lasting protection.īut what exactly are these ingredients? And why do some products work better than others with the same active ingredients? Here, answers to those questions and more. The list of products we recommend changes slightly from year to year, but insect repellents whose active ingredient is deet, at concentrations of 25 to 30 percent, reliably earn our recommendation, as do many (but not all) 15 percent deet sprays. And it turns out that what matters most is not the brand or type of repellent (spray, lotion, or wipe) but the active ingredient and its concentration. Then we measure how long it takes the bugs to start biting. Our brave participants place repellent-covered arms inside cages filled with 200 disease-free mosquitoes. But not all repellents provide equal protection, which is why CR tests how well each one blocks real bugs from biting real people.

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