If you put DEET on a cloth, it works for only around 17 days.

NPR: Mosquito War: New Chemicals May Beat DEET

"Any efforts to use any approach to improve on DEET should be commended, " Vosshall said.

NPR: Mosquito War: New Chemicals May Beat DEET

In his tests, some of the compounds repelled insect attack for far longer than DEET.

NPR: Mosquito War: New Chemicals May Beat DEET

The study looks at another approach to find something more potent, but with less worrisome side effects, than DEET.

NPR: Mosquito War: New Chemicals May Beat DEET

Leslie Vosshall, a scientist at The Rockefeller University in New York, is also on a mission to beat DEET.

NPR: Mosquito War: New Chemicals May Beat DEET

"And we're finding lots of interesting things that look nothing like DEET that are much more potent, at least in the lab, " Vosshall said.

NPR: Mosquito War: New Chemicals May Beat DEET

However, a few hours later when the same mosquitoes were offered a chance to dine again, the researchers found that the Deet was less effective.

BBC: Mosquitoes ignore repellent Deet after first exposure

"Which means, " Vosshall said, "that when you're spraying DEET on your skin or your clothes you're creating a microenvironment" that is effectively "blind" to odors.

NPR: Mosquito War: New Chemicals May Beat DEET

"After trying so many different repellents that people have submitted over the years, it was nice to see some that actually were better than DEET, " Bernier said.

NPR: Mosquito War: New Chemicals May Beat DEET

She found that DEET blocks the action of odor receptors.

NPR: Mosquito War: New Chemicals May Beat DEET

To find out more, researchers from the London School of Hygiene and Tropical Medicine took some A. aegypti mosquitoes in the laboratory, and tempted them with a human arm covered in Deet.

BBC: Mosquitoes ignore repellent Deet after first exposure