How mosquito repellant works

Sefior Mateo: Back in Boy Scouts, we had this ongoing debate about why exactly bugs hated bug repellent. Some claimed it was the smell. Others claimed it was the taste. Still others that it created a slick surface that the mosquitos couldn't land on. So what gives? Why exactly do the bugs get bugged by the bug spray? — Curious Dave, UCSD

As much as I like that picture of skeeters skidding off our oiled-up arms, I think we can junk that theory right from the top. And researchers now doubt that taste/smell (pretty much the same thing to a mosquito) has anything to do with it either. Scientists aren’t even sure exactly how mosquitos are attracted to us, much less why repellents happen to keep them away. With clear molecular-level explanations missing, you can imagine that research to find a better bug-stopper has been a hit and miss affair, so to speak. Beginning in ancient times, mankind figured out that certain things (smoke, citronella, pennyroyal among them) kept the biters at bay. Then, nobody cared why; now we care but can’t figure it out. But one of the primary forces in the assault on the mosquito mystery is the Department of Defense, so rest assured that many decades and misspent billions from now, we’ll have some sort of answer.

The DOD has confirmed one common notion that should settle a few family arguments, though. Certain people are better mosquito attractors than others. It seems to have something to do with their higher emissions of carbon dioxide, skin moisture, body heat, and/or some mysterious element of skin odor. Lactic acid, a metabolism byproduct, seems to figure into the mix somewhere too. These lead a skeeter to a blood source, but some as yet unidentified signal makes her actually land and “bite.” Repellants may somehow interfere with mosquitos’ ability to find us rather than making us too revolting to bother with. So mosquito “repellents” seem to be more like mosquito confusers. The newest triumph in the skeeter wars is a toxic substance that zaps the beasts when they land on your shirt and poke around for a likely site to drill. But I’m sure, all the while, mosquitos are hanging out with the cockroaches and chuckling over our dismal attempts to outfox them.