DEET guidelines make for a safe summer

The judicious use of repellents containing low levels of the chemical can help patients ward off insect-borne diseases.

By Susan J. Landers, amednews staff. June 16, 2003.

Washington -- It's mosquito and tick season, and patients are swarming to their physicians' offices with questions about how to protect themselves from insect-borne illness.

Unless these patients opt to cover up from head to toe or remain indoors until late fall, the use of an insect repellent is probably a necessity. And those that contain DEET are likely the best choice, experts agree.

Keeping the bugs off
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DEET "protects longer and is effective against more species of flying and crawling insects than other repellents," said Mark Fradin, MD, a dermatologist in private practice in Chapel Hill, N.C., and author of "Mosquitoes and Mosquito Repellents: a Clinician's Guide," Annals of Internal Medicine, June 1, 1998.

The main questions doctors may hear from their patients are: Do I need an insect repellent? Is DEET really safe? And, how much is too much?

Need is all too apparent. The Centers for Disease Control and Prevention receives reports annually of nearly 10,000 cases of Lyme disease and 1,000 reports of encephalitis.

Plus, there have been 3,893 human cases of West Nile virus in the United States in the last few years, with 254 deaths resulting. States are bracing for more as this year's mosquito season gets underway. Epidemiologists predict that the virus will spread to all 48 contiguous states.

200 million people use DEET each year, but EPA records show it caused harm in only 21 cases.

With the discovery that more mosquito species are capable of transmitting West Nile virus, the CDC now recommends applying a repellent before spending much time outdoors, whether day or night.

Developed by the U.S. Dept. of Agriculture, DEET was patented in 1946 by the Army. It has been approved for use by the general public since 1957. Of the approximately 200 million people who use it each year, there are only 21 cases on record of it causing harm, according to the Environmental Protection Agency.

Although DEET is a safe product, it does need to be applied with common sense. "On average more people over-apply than under-apply things like that," said Dr. Fradin. "Most consumers seem to think if a little will help then more is better."

Applying a repellent sparingly on exposed skin, but not around the eyes and mouth, is good advice. As for reapplication, a general guide should be, if insects aren't biting, the repellent is likely to be still working.

Although there are products that are 100% DEET, Michael Shannon, MD, chair-elect of the American Academy of Pediatrician's Committee on Environmental Health, recommends using products that have concentrations of 10% to 30%.

"We know that the only difference between 10% and 30% is how long insects are repelled," he said, "It's not a safety issue."

Products with concentrations of about 10% are effective for around two hours, according to the pediatric guidelines, while a concentration of about 24% provides an average of five hours of protection. If a day tramping through woods is on the agenda, a higher concentration of DEET is advisable rather than reapplying a lower concentration several times a day.

And despite the efficiency of two-in-one products, those that contain DEET and sunscreen should not be used. Not only does DEET reduce the effectiveness of the sunscreen, but the ideal application of each product is different, noted Dr. Fradin.

ADDITIONAL INFORMATION:

Keeping the bugs off

The Centers for Disease Control and Prevention and the American Academy of Pediatrics offer the following general considerations for the use of products containing DEET:

Use enough repellent to cover exposed skin or clothing. Don't apply repellent to skin that is under clothing. Heavy application is not necessary to achieve protection.
Do not apply repellent to cuts, wounds or irritated skin.
After returning indoors, wash treated skin with mild soap and water.
Do not spray aerosol or pump products in enclosed areas.
Do not apply aerosol or pump products directly to your face or on the hands of young children. Spray your hands and then rub them carefully over the face, avoiding eyes and mouth.