Insect Repellent: What To Look For

Is DEET safe?

While it's clear that DEET damages certain materials, its effects on human health aren't as easy to judge. Studies of DEET's effects on rats show that it's a neurotoxin that damages brain cells and decreases mental and motor abilities, but these effects have not been proven in humans. There are a few cases of children dying, contracting encephalitis or having seizures, apparently linked to exposure to DEET. Animal testing has also shown an increase in the chemical's toxicity while using Panretin, a topical drug for certain AIDS-related skin lesions. On the other hand, DEET has been used and studied for about 60 years -- more than any other insect repellent -- and judged relatively safe when used according to directions.

Canadian health authorities have stricter limits on insect repellents than do the corresponding agencies in the United States. So while the U.S. Center for Disease Control (CDC) says DEET is safe in high concentrations of up to 98 percent, even for children (but not babies under 2 months of age), Health Canada is limiting DEET concentrations to 30 percent and advising parents not to use any DEET on babies till they're at least 6 months old.

Pediatricians in Canada disagree as much as pediatricians in the United States do. One is quoted as saying that for every report of toxic effects caused by DEET, another 19 cases go unreported. Another says he'd use DEET on his own children as fast as they sweated it off, despite Health Canada's advisory. In the United States, a professor at Duke University warns that DEET can become much more toxic when a person is also exposed to other chemicals or is simply under stress -- and that children are especially vulnerable.

Both the CDC and the EPA have declared, however, that DEET is safe for most people when used according to directions. To use DEET insect repellent safely, label instructions say to use it only on exposed skin, never under clothing. When you come back indoors, you're supposed to wash it off your skin and change any clothes to which you've applied it. This is inconvenient, and experts estimate that many users don't follow these guidelines.

All in all, whether or not DEET is safe to use is one of those issues that each user (and parent) will have to decide based on personal risk assessment. Even Health Canada advises using higher concentrations of DEET when traveling into parts of the world where mosquitoes carry malaria or dengue fever. If there are outbreaks of West Nile virus or encephalitis in your area -- diseases that just one mosquito bite can carry -- the known danger of the diseases can easily outweigh doubts about the safety of DEET. On the other hand, the World Health Organization (WHO) recommends picaridin even for malaria-ridden areas, so that's another alternative.

Synthetic insect repellents, DEET and picaridin, are more effective than natural repellents. Lemon eucalyptus oil and geranium or soybean oil are the most effective natural insect repellents. While they do not provide the long-lasting protection of synthetic repellents, they can be applied more frequently.

Experts offer the following tips for using insect repellents:

• Test any new insect repellent on a small area of skin first. The inside of the elbow is a good testing spot. Anyone can prove allergic to an ingredient, so test first.

• Read and follow all directions on the product label. Apply sparingly, especially on young children. If the repellent doesn't damage fabric, apply it to the outside of clothing where possible, rather than directly to skin.

• Do not apply over cuts, wounds or irritated skin -- or near eyes and mouths of young children. Do not spray in enclosed areas. Do not use under clothing.

• Use separate insect repellent and sunscreen products. A 2004 study conducted by University of Florida researchers determined that using DEET combined with sunscreen could increase skin absorption. If you need both sun protection and insect repellent, reviews say you should apply sunscreen first, wait for it to dry, then apply insect repellent. For sunscreen suggestions, see our separate report on sunscreens.

• In general, insect repellents aren't recommended for children under 2 months of age. Health Canada recommends waiting until kids are 6 months old. Protect babies with mosquito netting. Oil of lemon eucalyptus isn't recommended for children under age 3. Pregnant and nursing women should consult physicians before using insect repellents.

• Be proactive about preventing mosquitoes from laying their eggs. Keep the yard and house free of containers filled with standing water. Stay indoors when most mosquitoes are active, beginning at dusk and throughout the evening. Wear light-colored, loose-fitting clothing that covers as much skin as possible.

• Wash DEET-treated skin with soap and water after returning indoors. Remove and wash treated clothing. (If you've sprayed clothing with a permethrin repellent, you can store it in plastic bags to keep it potent longer.)

Area insect repellent

Both allethrin (often found in lamps) and metofluthrin (found in strip devices and diffusers) have been approved by the Environmental Protection Agency as area-wide mosquito repellents. We didn't, however, find much research backing their effectiveness, but Good Housekeeping lists information about popular commercial devices. For instance, allethrin lamps, such as the OFF! PowerPad Lamp (*Est. $12 for lamp, candle and repellent pad) and the ThermaCell Patio Lantern (*Est. $30 for butane cartridge and allethrin lamp), are purported to offer 93 to 99 percent protection from mosquitoes and sand flies in a 15-foot area for up to four hours. Metofluthrin, as found in the OFF! Clip On (*Est. $10 for fan unit and refill), provides 84 to 100 percent protection from mosquitoes with the help of a personal diffuser.

Good Housekeeping also recommends geraniol candles and diffusers, such as the Koolatron Mosquito Repelling Candle (*Est. $18 for 1.2 lb. candle). They only provide up to 80 percent protection from mosquitoes in a 10-foot area, however. If you live in an area where insect-transmitted diseases are prevalent, a stronger personal repellent is suggested.