DEET, one of the world's most popular topical insect repellents, actually works by hiding your natural smell.
If you travel to a malarial country, you're strongly advised to cover up and use insect repellent. Malaria affects an estimated 500 million people each year and is responsible for roughly 1 million deaths annually. Avoiding being bitten is a good way to avoid the disease. For this reason, the insect repellent DEET was developed fifty years ago by the US Army. We know DEET works to repel a wide range of insects, but only now have scientists discovered how it works.
Mosquitoes are strongly attracted to the odours given off by living, breathing animals. They use the smells of sweat and the CO2 given out in breath to home in and find food – namely blood. Insect repellents work in one of two ways: insects can find the smell itself distasteful and so stay away, or the chemical can somehow 'blind' the insects to the food smells they look for.
Writing in this week's Science, Mathias Ditzen and colleagues at the Rockefeller University in New York tested the electrical activity of cells in the Mosquito olfactory system. These cells have receptors on the surface for the attractive sweaty smells, and so their electrical activity increases in the presence of a potential meal. When exposed to DEET, certain receptors are shut down, effectively 'blinding' the insect to the tempting sweaty smells.
But DEET doesn't just shut down the insect sense of smell, it selectively acts on a small co-receptor called Or83b. This receptor is found in all insects, and is needed to detect sweaty odours. Even in the presence of DEET, insects can detect CO2 as this doesn't need the co-receptor to work.
DEET is very widely used but can lead to skin irritation and potential health risks. Knowing how it works means we can start to develop repellents at least as effective as DEET, but without the side effects.