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What Makes DEET Effective Against Mosquitoes?

09 September, 2008

Having a repellent that effectively deters mosquitoes and other insects, as well as ticks, has assumed ever greater importance considering the host of illnesses spread by these pests. DEET is the most widely used active ingredient in insect repellents, used by about 200 million people worldwide, and is considered to be unequaled when it comes to keeping bugs away. The long-held belief has been that DEET works by interfering with the mosquitoes` sense of smell and by masking the smell of their target, but researchers have discovered that is not the case. It turns out they simply don`t like the smell!

Chemical ecologist Walter Leal, Ph.D., professor of entomology at University of California, Davis and his colleagues set up odorless sugar-feeding stations, some containing DEET, and found that DEET actively repelled Southern house mosquitoes, which can carry West Nile Virus, St. Louis encephalitis, and lymphatic filariasis, a disease caused by threadlike parasitic worms. "We found that mosquitoes can smell DEET and they stay away from it," Leal said in a news release. "DEET doesn`t mask the smell of the host or jam the insect`s senses. Mosquitoes don`t like it because it smells bad to them."

However, the breakthrough moment was when he and researcher Zainulabeuddin Syed, Ph.D., discovered the exact neurons on the antennae that detect DEET, which are located beside other neurons that sense a chemical, 1-octen-3-ol, known to attract mosquitoes. "I was so delighted when I first encountered the neuron that detects DEET, a synthetic compound," said Syed. "I couldn`t believe my eyes because it goes against conventional wisdom so I repeated the experiment over and over until we discussed the findings in the lab."

While understanding how DEET works may not be as important to consumers as the fact that it works well, these new findings could lead to better disease prevention by helping researchers identify other compounds that work similarly in repelling mosquitoes and other insects. "Despite the fact that DEET is the industry standard mosquito repellant, relatively little is known about how it actually works," UC Davis research entomologist William Reisen said in the news release. "Previous studies have suggested a ‘masking` or ‘binding` with host emanations. Understanding the mode of action is especially important because DEET is used as the standard against which all other tentative replacement repellants are compared."

DEET-based repellents are recommended by the Centers for Disease Control and Prevention (CDC), the National Institute for Occupational Safety and Health (NIOSH), the American Academy of Pediatrics (AAP), and state and local public health officials nationwide. According to AAP, they can be used on all family members over the age of two months in concentrations up to 30 percent. Typically, the more active ingredient a product contains the longer it provides protection from mosquito bites. Based on a 2002 study:

Products containing 4.75 percent DEET provide roughly 1 ˝ hours of protection.

A product with 6.65 percent DEET provides almost 2 hours of protection.

A product containing 20 percent DEET provides almost 4 hours of protection.

A product containing 23.8 percent DEET provides an average of 5 hours of protection.

You should choose a repellent based on the amount of time you plan to be outdoors. If you are outdoors longer than expected and start to be bitten, simply re-apply repellent, following label instructions. These products are available in many formulations, including lotions, creams, gels, aerosol and pump sprays, as well as towelettes.

The UC Davis study, "Mosquitoes Smell and Avoid the Insect repellent DEET," was published in the August 18 edition of the Proceedings of the National Academy of Sciences.


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