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DEET Blocks Bugs From Smelling Humans as "Food"

Brian Handwerk
for National Geographic News
March 13, 2008
 
The popular bug spray known as DEET blocks insects from picking up the smells on humans that would otherwise register as "food," a new study says.

The finding could help solve the 50-year-old mystery of exactly how the powerful human-made repellent keeps mosquitoes and other pests at bay.

Many consumers have long believed that strongly scented DEET also smells bad to insects and causes them to steer clear.

But according to the new research, DEET temporarily destroys an insect's sense of smell by hindering the function of certain odor receptors.

"From far away they start smelling you," said study co-author Leslie Vosshall of the Rockefeller University in New York City.

"Then they encounter a cloud of DEET and their olfactory system is jammed and they can't find you."

Powerful and Mysterious

Scientists at the U.S. Department of Agriculture invented DEET in 1958, but at the time no one fully understood how it worked.

"They found it more or less by trial and error," Vosshall said.

"I assume they found compounds off the shelf and tested them for their ability to make mosquitoes go away. Then they tinkered with molecules to make them safer and more effective."

(Related news: "Frog 'Juice' May Be Next Big Bug Repellent" [July 24, 2006].)

Morflex, Inc., the world's largest DEET manufacturer, estimates that about 200 million people around the globe use the repellent each year.

"The amazing thing is that [DEET] works on almost any insect that has been tested," Vosshall said.

"That made me suspicious that there's something that insects have in common that makes them susceptible to the stuff."

In studies done with fruit flies, Vosshall keyed on a scent-enabling protein that exists only in insects.

The olfactory protein—known in fruit flies as OR83b—is governed by genes so similar that Vosshall has interchanged them between species, including mosquitoes and corn moths.

"All along I was thinking that this was a reasonable molecular target for DEET."

Jonathan Day, with the Florida Medical Entomology Laboratory at the University of Florida, said he found the recent research interesting.

Though Vosshall's group primarily studied the impact of DEET on fruit flies, their findings seem to mirror the way Day has observed mosquitoes react to the chemical.

"When you do lab tests with DEET, repellent is a bit of a misnomer," he said.

"Mosquitoes will come right up and actually touch the skin that has the repellent on it. But then they become noticeably agitated and they are unable to land and initiate blood feeding."

"Usually they will go to the side of a cage and sit for hours" after encountering DEET, he said.

Day thinks the insects might be waiting to clear their systems of the odor blocker before starting the hunt for another meal.

Gold Standard

Day notes that no bug repellent developed before or since DEET has been as powerful.

"As you'd imagine, the competition to find a product as effective as DEET is very strong," he said.

(Read "Beat Bugs Without DEET: U.S. Boosts 2 Alternatives" [July 26, 2005].)

"Every year thousands of different products are screened, but DEET is always referred to as the gold standard. Nothing else compares."

Agencies such as the U.S. Centers for Disease Control and Prevention and the UN World Health Organization continue to certify DEET as safe.

Many consumers, however, worry about potential side effects of using the chemical, such as rashes and seizures.

In addition to the olfactory effects on insects, Vosshall's team has found another potential red flag for humans.

"The surprising thing we found is that at the nitty-gritty cellular level, it inhibits a class of human proteins called ion channels, which are very important to the function of the human nervous system," Vosshall said.

"We suggest that this might be of concern."

Still, she said, the new study could ultimately prove a boon to be for developers of improved or even DEET-free repellent products.

"To me it's all good news," Vosshall said. "You can only improve on past [technologies] if you understand how they work."

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