Because West Nile virus has made preventing mosquito bites more important in the United States, and because some insecticides are toxic, people have become increasingly concerned with finding gentle and effective solutions at preventing mosquito bites. DEET is the most effective ingredient at preventing mosquito bites. It does not kill mosquitoes, but repels them, discouraging them from biting.

Although DEET is recommended for pregnant and nursing women, we do know that DEET is absorbed through the skin. It crosses the placenta in pregnant women and into the breast milk of those who are nursing. This may be worth the exposure, though, because West Nile virus infections can also cross the placenta, and may pass into breast milk.

Researchers at Chapel Hill Dermatology and the Florida Medical Entomology Laboratory tested 16 different mosquito repellants on 15 volunteers who thrust their arms into cages full of mosquitoes. Four of the products contained DEET, the others were plant-based products. The results were published in the July 4, 2002 New England Journal of Medicine. Bite Blocker for Kids, whose active ingredient is soybean oil, was the most effective of the natural products – working well for an average of 94 minutes in the cage after application. The CDC suggests soybean oil products when looking for a DEET alternative. Herbal Armor (a combination of citronella, peppermint oil, cedar oil, lemongrass oil, and geranium oil) worked well for about 19 minutes. Various Skin-So-Soft products were effective for an average of 3 to 23 minutes in a cage full of mosquitoes. Cage studies, however, may underestimate how well products work in the backyard, where mosquitoes have someplace else to go.

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Alan Greene MD contributor

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