Study shows mosquito repellents with DEET most effective

By Stephanie Nano, The Associated Press
Thursday July 04, 2002

Just in time for your July Fourth outing, a study concludes that insect repellents containing the chemical called DEET provide the best protection against mosquito bites. 

Bug sprays and lotions that rely on plant oils or another chemical don’t last as long and might require several applications, according to the report in Thursday’s New England Journal of Medicine. Three repellent wristbands tested didn’t work at all. 

“I don’t think there’s anything wrong with using alternatives and I don’t think DEET is a perfect repellent. But it is still more effective and very safe,” said one of the researchers, dermatologist Dr. Mark Fradin of Chapel Hill, N.C. 

DEET has been on the market since 1957 and a 1998 review by the Environmental Protection Agency deemed normal use safe. Yet many consumers are reluctant to use DEET and seek out alternatives, the researchers said. 

Knowing which repellent works best is important when used to protect against mosquito-transmitted diseases such as West Nile virus, they said. 

Fradin worked with Jonathan Day of the Florida Medical Entomology Laboratory in Vero Beach to test the effectiveness of 16 products. 

Each was tested three times on 15 workers at the University of Florida lab using a design Day said was devised for a student’s ninth-grade science fair project. The student said she’s sensitive to bug bites and sought out Day’s help for a smaller test of repellents. 

For the study, each worker applied repellent, put their arm into a cage with 10 mosquitoes for a minute and reinserted it at intervals until the first bite. 

The DEET-based products offered complete protection for the longest time, and higher concentrations worked best, the researchers said. The highest concentration tested, about 24 percent in OFF! Deep Woods, lasted for five hours on average. Sawyer Controlled Release, with 20 percent DEET, worked for about four hours. 

A soybean repellent worked for about 1 1/2 hours while other plant-derived repellents, including citronella, lasted less than 20 minutes. Three wristbands — two with DEET and one with citronella — provided no protection. 

After the study was completed, repellents using oil of eucalyptus were introduced in the United States. In a preliminary test, a eucalyptus repellent worked for about two hours. 

Included in the study were four Avon products, including a moisturizer that some people claim wards off bugs and Avon’s Skin-So-Soft Bug Guard Plus with a chemical called IR3535. 

The moisturizer, Skin-So-Soft Bath Oil, worked for less than 10 minutes and the Bug Guard Plus protected for an average of about 23 minutes, according to the study. 

Janice Teal, chief scientific officer for Avon Products Inc., noted that the moisturizer isn’t sold as a repellent and questioned doing such a study in a lab. In a field test, she said, the Avon repellent worked as well as a DEET-based repellent, protecting against mosquito bites for four hours. 

“We feel that in a real-world condition our product clearly works,” she said.