DIY Network

Best Way to Keep Bugs at Bay on a Summer's Day

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By Donna Halvorsen
Minneapolis-St. Paul Star Tribune
June, 2003

To slap or to slather. That is the question as more than a dozen species of mosquitoes buzz around this summer, looking for juicy pieces of unprotected skin to bite. People who have grown tired of slapping have looked for repellents less harsh and less smelly than those containing DEET, an active ingredient in mosquito repellents since 1957. But while essence of peppermint or lemon grass might be more pleasant, studies show that botanical products don't have anywhere near the clout of DEET products. DEET "remains the best deterrent," Consumer Reports said in its May issue. "Don't expect much from (non-DEET) repellents."

In lab tests of nine repellents, the magazine found two DEET products to be the most effective against mosquitoes and ticks: Ultrathon, developed by 3M, and Off Deep Woods for Sportsmen, made by SC Johnson of Racine, Wisconsin. Both kept mosquitoes at bay for 13 hours. But Off Deep Woods for Sportsmen has three times as much DEET (100 percent) as does Ultrathon, and physicians urge using as little DEET as possible. Consumer Reports also found that Ultrathon kept ticks away for 10 hours and Off for seven hours.

3M developed Ultrathon in lotion form for the U.S. military. The product contains a polymer, a molecule that keeps the repellent on the skin rather than being absorbed into the body or evaporated into the air. The product also was rated highly by the Medical Letter on Drugs and Therapeutics, which said in its May 26 issue that it provides "more than 95 percent protection against mosquito bites for six to 12 hours, depending on environmental conditions and the species of mosquito." A spray version was put on the market about a year ago. A 3M spokeswoman said it offers protection for eight hours.

West Nile virus has changed the equation in the slap vs. slather debate. The virus, which killed 284 people nationwide last year, is expected to return for a second year on the wings of the Culex tarsarlis mosquito. Still, David Neitzel, an epidemiologist with the Minnesota Health Department, said the risk to people is small. "There aren't very many infected mosquitoes out there," Neitzel said. "It's going to be well less than 1 percent of the mosquitoes around that are actually carrying the virus." Nonetheless, he said, people should be aware of the virus -- especially the elderly, who are at greater risk for the most severe West Nile illnesses such as encephalitis, an inflammation of the brain.

The essential questions about insect repellents are:

1. How long do they protect against bites?

2. How strong must a formula be to achieve that degree of protection?

3. Are they safe?

Toxic and allergic reactions are rare, Zuccotti said. In the Journal of the American Medical Association last year, a researcher wrote, "DEET has a remarkable safety profile after 40 years of use and nearly 8 billion human applications. Fewer than 50 cases of serious toxic effects have been documented in the medical literature since 1960, and three-quarters of them (were) resolved without (aftereffects)." The Medical Letter also says that when DEET products are used according to directions, "concentrations up to 50 percent appear to be safe even in young children."

That's a point of contention. Some health experts recommend much lower doses for children. "For children, you can use a DEET repellent of 10 percent or less, and that'll work just fine," Neitzel said. "My own family uses a 7 percent DEET solution, and it gives you the same protection as the more powerful DEET concentrations." The only difference is that it won't last as long.

Health Canada, the government's health department, recommends that DEET concentrations of 10 percent or less be used on children, and that repellents be used in small amounts for short periods. The government has banned concentrations above 30 percent. The Medical Letter said no chemical used in insect repellents on the U.S. market works as long as DEET does. The highest-ranked botanical product, based on eucalyptus, was found to keep mosquitoes away for up to four hours.

Permethrin, an insecticide rather than a repellent, is normally used to treat lice, but it's being marketed to keep mosquitoes and ticks away from clothing, mosquito nets, tents and sleeping bags. The spray product is meant to be applied to the outside of fabrics, not to the skin. It stays in clothing up to 20 washings and has been shown to be effective, Zuccotti said. According to the Medical Letter, permethrin is toxic to the nervous system of insects but is poorly absorbed and rapidly deactivated in mammals; there have been few signs of skin toxicity, such as redness or rash, or of any other problems, the letter said.

(Donna Halvorsen is at dhalvorsen@startribune.com. Distributed by Scripps Howard News Service, www.shns.com.)