Spray it on: everyone wants a better, friendlier insect repellent. Credit: CDC

Anyone who has sprayed their skin with the insect repellent DEET and then picked up a plastic water bottle has probably felt a twinge of concern as the bottle starts to disintegrate in their hands. A new study pinpointing exactly how the repellent works will hopefully lead the way to other chemicals that have the same (or better) insect-deterring effect without the inconvenience of dissolving plastic.

DEET is a very effective mosquito repellent and, despite its material-destroying capabilities, is safe for use on skin. But it can be an irritant and is a strong solvent, so it should not be used near a tent, synthetic clothes or near an open wound. This makes it less convenient than more-natural but less-effective repellents, such as citronella.

Now, Leslie Vosshall and her colleagues at The Rockefeller University in New York have pinpointed how DEET works. In mosquitoes, it stops neurons that sense human odours from working properly, they report in Science1. It does not affect mosquitoes' abilities to sense carbon dioxide from human breath, as some people had suspected.

The result should help researchers to scan a host of other chemicals for the same property, hopefully yielding a friendlier, effective repellent.

Smells like sweat

“This paper is important in that it provides the first chemical mechanism for how DEET works,” says Larry Zwiebel of Vanderbilt University in Nashville, Tennessee.

In particular, the work shows that DEET interferes with a molecular complex in mosquitoes that normally responds to 1-octen-3-ol, a chemical that people sweat and exhale. This interference means that a mosquito encountering DEET loses interest in a juicy human target.

“Imagine you are [a mosquito and you are] flying upwind. You smell the carbon dioxide in human breath. You get a whiff of 1-octen-3-ol, which is really volatile. But then as you get close, you meet the cloud of DEET,” says Vosshall. “It’s as though the target has disappeared.”

Frog test

To confirm that DEET interferes with the receptors for 1-octen-3-ol, the researchers transplanted these receptor molecules from mosquitoes into a 'blank-slate' set of cells (in this case frog’s eggs), added DEET, and checked the electrical currents in the cell membrane. A change in current confirmed that DEET was indeed acting on these receptors.

Vosshall and her team plan to put this information to good use. They aim to screen hundreds of thousands of chemicals in a search for one that is even more effective than DEET at interfering with these and other receptors that sense human odours, but have none of the unwanted side effects.

But a repellent that doesn't dissolve your water bottle can only be found if the properties that cause DEET to destroy plastics are different from those that inhibit aspects of insect smell, which, as Vosshall admits, no one yet knows.