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DEET Rules as a Mosquito Repellent

Despite urban legend, Skin-So-Soft and other plant-based products don't provide much protection against mosquitoes.

Numerous insect repellents are available in the U.S. for protection against mosquito bites; active ingredients generally are either synthetic chemicals or plant-derived essential oils. In this study, researchers used a standard protocol to measure the protection afforded by 16 commercially available products; 15 volunteers applied each product 3 separate times to the forearms and hands and, after each application, inserted their arms into test cages that contained 10 mosquitoes.

Products that contained the chemical N,N-diethyl-3-methylbenzamide (DEET) performed best, and duration of protection was proportional to DEET concentration (mean protection times until first bite; 302, 234, 112, and 88 minutes, respectively, for DEET concentrations of 23.8%, 20%, 6.6%, and 4.8%). Average protection time for another chemical ingredient (IR3535) was only 23 minutes. Mean protection times for plant-based products were 95 minutes for 2% soybean oil, 3 to 20 minutes for products containing various concentrations of citronella, and 120 minutes for a recently marketed, eucalyptus-based repellent. Skin-So-Soft bath oil, believed by many consumers to repel mosquitoes, yielded only 10 minutes of protection. Wristbands impregnated with DEET or citronella provided no protection.

Comment: Clearly, DEET-based products are the most effective mosquito repellents that are available currently. The authors note that DEET has an excellent safety record after 40 years of use. For brief periods of protection, several essential oils are better than no protection at all.

— Allan S. Brett, MD

Published in Journal Watch General Medicine July 12, 2002

Citation(s):

Fradin MS and Day JF. Comparative efficacy of insect repellents against mosquito bites. N Engl J Med 2002 Jul 4; 347:13-8.

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