Mosquito Repellents: What Works

Mosquitos don't just whine in your ear and drive you mad with itching, but they also spread disease to more than 700 million people every year. Here's how to stay off a mosquito's menu.

Who's For Lunch?

Do you seem to get eaten alive when others are left alone? You're probably not just imagining it.

Everyone's body chemistry is a little different, and some people are more likely to attract unwanted insect advances than others are.

Mosquitoes can sense your presence from far away. When you breathe out, you emit a plume of carbon dioxide that carries on the breeze, and CO2 also seeps from your skin.

Mosquitoes are attracted to carbon dioxide as well as the warmth and humidity you're giving off, says Renee Anderson, PhD, a medical entomologist at Cornell University in Ithaca, N.Y. They follow the trail, flying in a zigzag pattern, until they find the source. In addition, they are also attracted to certain chemicals in your sweat. And mosquitoes love a moving target -- it helps them zero in.

How to Stay Off the Menu

In general, mosquito repellent works by masking the chemical cues that welcome mosquitoes to dine.

DEET: Potent, But Safe

One of the most effective mosquito repellents is one of the oldest around. DEET was first developed for use by the U.S. Army in 1946, and it became available to the public in 1957. Many other products have hit the market since then, but few compare to DEET. In fact, it's one of two ingredients in mosquito repellent that the CDC recommends for preventing mosquito-borne diseases. The other is picaridin, and the CDC believes these two ingredients are more effective than other mosquito repellents.

In a study published in the New England Journal of Medicine in 2002, researchers compared several types of mosquito repellents head-to-head in laboratory tests. Fifteen brave study volunteers took turns sticking an arm treated with mosquito repellent into a cage full of hungry bloodsuckers. The researchers took note of how long it took a mosquito to bite.

"OFF! Deep Woods" repellent, a product containing about 24% DEET, fared the best. Its protection lasted an average of five hours.

The least effective products were wristbands treated with DEET or citronella, which offered almost no protection. According to the researchers, this wasn't a surprise. It's known that mosquito repellent only works on the surface to which it's applied directly. Mosquitoes are happy to bite skin only four centimeters away from the repellent slick.

DEET has an excellent safety record, despite some people's concerns. N,N-diethyl-3-methylbenzamide doesn't sound like something you'd want to spray on your skin, and perhaps its acronym reminds people of the dangerous and now banned insecticide DDT. They're nothing alike, however.

The Environmental Protection Agency must approve all pesticides used in the U.S., and although DEET isn't a pesticide by definition -- it does not kill insects -- it falls under the EPA's regulatory purview.