Taming the Backyard Menace: Beware of the Health Hazards of Common Mosquito Repellent

Full letter as submitted to the Washington Post by Jay Feldman, executive director, Beyond Pesticides, published July 19, 2002

As children get slathered with mosquito repellents this summer, the article, "Herbals Lag as Mosquito Repellents," (Washington Post, p1, July 4, 2002), focuses on product efficacy with inadequate attention to product safety. An effective product that can harm children's developing nervous system is not the solution that parents want. Researchers at Duke University Medical School (led by Dr. Mohamed Abou-Donia) have published findings demonstrating in laboratory studies that frequent and prolonged application of DEET cause neurons to die in regions of the brain responsible for muscle movements, learning, memory and concentration --all subtle effects. Laboratory animals exposed to average human doses of DEET perform far worse than untreated animals on neurobehavioral tasks requiring muscle coordination. Even more alarming are researchers' findings that low dose exposure to DEET in combination with some pesticides sprayed by truck or aircraft for West Nile Virus show a synergistic or severely increased neurological effect. In April, Canada banned repellents with more than 30% DEET, as well as those mixed with sunscreen.

Close scrutiny of the new EPA-required DEET label, which takes full effect this summer, reveals serious warnings that are not likely to be strictly followed, including: Do not apply over cuts, wounds, or irritated skin; do not apply to hands or near eyes and mouth of young children; do not allow young children to apply this product; use just enough repellent to cover exposed skin and/or clothing; do not use under clothing; avoid over-application of this product; after returning indoors, wash treated skin with soap and water; wash treated clothing before wearing it again; use of this product may cause skin reactions in rare cases; do not spray in enclosed areas.

Given the scientific findings and EPA use precautions for DEET, it is prudent to use protective clothing and choose the most effective natural-based product, even though it may require reapplication. Insect-borne diseases can pose a serious threat to public health, therefore state governments and local jurisdictions must get serious about mosquito prevention by eliminating breeding sites, educating on homeowner steps, and effectively managing mosquitoes at the larval stage before they become biting adults.


Jay Feldman
executive director
Beyond Pesticides

For more information visit Beyond Pesticides' mosquito page or read Dr. Abou-Donia's study on the synergistic effects of DEET and permethrin, the active ingredient used by many communities for mosquito control.

Herbals Lag as Mosquito Repellents
DEET-Containing Products Far More Effective, Study Finds

By Susan Okie
Washington Post Staff Writer
Thursday, July 4, 2002; Page A01

Most insect repellents containing herbal oils are far less effective than those containing DEET, a synthetic chemical marketed since the 1950s, according to the first study to scientifically compare a wide range of products.

Although the botanical repellents have attracted chemical-wary consumers, the findings suggest that DEET-containing repellents would be the best choice for anyone seeking reliable protection from mosquito-borne or tick-borne infections such as West Nile virus or Lyme disease, said researcher Mark S. Fradin, co-author of the study in today's issue of the New England Journal of Medicine.

"If I was traveling to Africa and had to worry about getting malaria or . . . yellow fever, I would want a DEET-based product on my skin," said Fradin, a dermatologist at the University of North Carolina.

Dozens of insect repellent creams, sprays and lotions contain various concentrations of DEET, or N,N-diethyl-3-methylbenzamide, which was developed in 1946 by the Department of Agriculture for use by the military. Other products have active ingredients such as citronella, oil of eucalyptus, peppermint oil, soybean oil and IR3535, or Ethyl-Butylacetylamino-propionate, a biopesticide popular in Europe, but new to the United States, that is chemically similar to the naturally occurring amino acid alanine.

Scientists are not certain how insect repellents work but theorize that they block the sensory receptors that mosquitoes and other biting insects use to detect carbon dioxide, lactic acid and other chemicals given off by their human or animal targets.

Because no one had compared various repellents' effectiveness, Fradin and entomologist Jonathan F. Day of the University of Florida decided to test 17 nationally marketed products under laboratory conditions. They asked 15 volunteers at the Florida Medical Entomology Laboratory in Vero Beach to stick a forearm coated with repellent into a cage containing 10 hungry female mosquitoes and see how much time elapsed before the first bite.

Each repellent was tested three times on each subject, to ensure that results were consistent and reliable. The researchers used Aedes aegypti, a species of mosquito that is the carrier of dengue fever and yellow fever and that bites readily at any time of day. Laboratory mosquitoes were disease-free.

Volunteers left their arms in the cages for a minute at a time, then removed them and repeated the procedure at regular intervals, said research technician Nazar Hussain, who participated in the study. "With some products, you would just put your hand in there and they would start coming within five seconds," he said.

Four skin lotions containing DEET in concentrations ranging from 5 percent to 24 percent were among the top six tested. Off! Deep Woods, a repellent containing 23.8 percent DEET, provided the longest-lasting protection: 302 minutes, on average. The other DEET lotions worked for at least 89 minutes. But wristbands, containing DEET or citronella, were completely ineffective.

Two botanical repellents performed as well as some DEET-based products. One, containing oil of eucalyptus -- Repel Lemon Eucalyptus Lotion Insect Repellent, which is also marketed as Fite Bite Plant-Based Insect Repellent -- protected participants for an average of 120 minutes. Another, containing 2 percent soybean oil, Bite Blocker for Kids, worked for an average of 95 minutes.

None of the other repellents tested -- containing IR3535, citronella, or oils of peppermint, lemongrass, geranium or cedar -- worked for longer than 22 minutes. Avon Skin-So-Soft Bath Oil, which Fradin said he chose to test because of its "mythical status" among some consumers, failed after 9.6 minutes, on average.

"The thing that surprised me was the gigantic difference between the DEET-based repellents and, for the most part, the non-DEET-based repellents," Fradin said.

Consumers have applied DEET more than 8 billion times in the past 45 years, and its overall safety record is excellent, researchers said. Fradin said there have been about 50 cases of significant toxicity, generally involving high doses or deliberate ingestion.

There have been seven reports of seizures in small children who were exposed to excessive doses of DEET, said Andrew Spielman, a professor of tropical medicine at the Harvard School of Public Health who co-wrote a commentary on the study. He said repellents containing about 35 percent DEET provide mosquito protection lasting overnight, and products with higher concentrations offered no additional benefit. He recommended that less-concentrated DEET products should be used for children.

Spielman noted that Aedes aegypti is somewhat more easily repelled than the deer ticks that carry Lyme disease or the mosquito species that carry malaria and West Nile virus. He added that the many gadgets marketed to repel mosquitoes -- including lights, coils and devices that produce sound or carbon dioxide -- have not been scientifically evaluated.

Insect repellents are regulated by the Environmental Protection Agency. Spielman said product labeling typically provides little guidance for users. "It's terribly important that there be some way for the consumer to understand how much of the material should be applied" and how often, he said.

EPA spokesman Dave Deegan said the agency is revising its guidelines for the labeling of repellents, as well as requirements on how much proof of effectiveness manufacturers must provide.

"We were really happy to see this study," said Susan E. Little of the Consumer Specialty Products Association, which represents companies that manufacture many of the repellents tested. She acknowledged that labeling is frequently vague. She said the industry "would be more than happy if the EPA came up with a consistent, across-the-board labeling procedure for all products, including the botanicals and the naturals."