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Janice J. Teal, Ph.D.
Avon Products
Suffern, NY 10901
Editor's note: Dr. Teal is group vice-president and chief scientific officer, global research and development, Avon Products. Avon manufactures insect-repellent products for sale in the United States and overseas.
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In addition, the amount of material applied and the concentration used can account for significant differences in the results. One of the products tested was Skin-So-Soft Bath Oil, which is not a repellent.
Both the published information on DEET-based repellents and the information in the mass-media promotion state that the repellents can be relied on to provide prolonged protection in environments where mosquito-borne diseases are a significant threat. This is a false assumption and has never been proved. These statements are also harmful, since laypeople are given a false sense of security, believing that if they use a DEET-based repellent, they will be totally protected from arthropod-borne pathogens. The Scientific Advisory Board of the EPA also agreed that no manufacturer of repellents could make such a statement of protection from mosquito-borne diseases.
Eugene J. Gerberg, Ph.D.
University of Florida
Gainesville, FL 32611
Robert J. Novak, Ph.D.
Illinois Natural History Survey
Champaign, IL 61820
Editor's note: Drs. Gerberg and Novak served on the EPA's Scientific Advisory Panel on repellents.
It would be useful to know whether the highest concentrations offer a significant benefit over those studied. Although the health risks of 95 percent DEET may be minimal, the risk of damage to plastic watches, pens, and camera bodies might be lessened with lower concentrations.
Steve Gerrish, M.D.
Bristol Bay Area Health Corporation
Dillingham, AK 99576
stevegerrish{at}yahoo.com
35 percent) may be appropriate for those who are exposed for many hours to numerous black flies or mosquitoes or who work in tick-infested areas."1 We agree that DEET is preferred for preventing bites from black flies or mosquitoes, but permethrin has been proved to be more effective for ticks.2,3,4 The effect of permethrin is predominantly acaricidal rather than repellent.3,4 Although it can be safely applied to the skin, permethrin remains effective longer when applied to clothing, netting, or tents and can withstand several washings.2,3,4 In the U.S. military, the concurrent application of DEET repellent on the skin and permethrin on the battle dress uniform is officially known as the DOD (Department of Defense) Insect Repellent System. This combination provides the best-known protection against arthropod bites and the transmission of arthropod-borne diseases to troops in the field.4
David R. Adams, M.D., Pharm.D.
Bryan E. Anderson, M.D.
Christie T. Ammirati, M.D.
Penn State Milton S. Hershey Medical Center
Hershey, PA 17033
dadams{at}psu.edu
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Not only is vitamin B1 much less expensive than other repellents, but it also is nonwetting, is not oily, and is not rubbed off on clothes.
Stewart C. Harvey, Ph.D.
900 S. Donner Way, #404
Salt Lake City, UT 84108
George Brownstone, M.D.
Girardigasse 3/23
A 1060 Vienna, Austria
georg.brownstone{at}chello.at
To the Editor: Teal is correct that the recommendation of the EPA's Scientific Advisory Panel (in April 2000) was that "only field studies be used to establish efficacy and subsequent registration"1 of new repellents. Teal neglects to mention, however, that the panel also stated that cage studies "can be used to compare products."1 In our article, we explained the rationale for using the arm-in-cage method. It would have been impossible to conduct a valid comparative field study of this size, given the multiple environmental variables that affect biting rates. With West Nile virus now found throughout the United States, the ethics of requiring field trials may need to be examined by the EPA, which has not yet adopted the recommendations of the panel.
Our decision not to standardize the amount of repellent each subject applied was deliberate. We wanted our study to reflect real-life usage, and application quantities are not stated on repellent labels. In our experience, repellents are typically overapplied, not underapplied, so we are confident that our subjects applied sufficient quantities of repellent to make it possible to judge each one's relative efficacy.
Gerberg and Novak properly emphasize that persons should not rely solely on insect repellents for the prevention of insect bites and insect-borne diseases. As we stated twice in our article, "Protection from arthropod bites is best achieved by avoiding infested habitats, wearing protective clothing, and using insect repellent." We agree with Adams et al. that the combined use of the contact insecticide permethrin on clothing and DEET on the skin results in a formidable barrier, providing a level of protection against mosquito bites as high as 99.9 percent, even under conditions in which unprotected subjects received an average of 1188 bites per hour.2
Gerrish asks why we did not test products containing more than 23.8 percent DEET. Other than a few 95 percent DEET products, all DEET products on the U.S. market contain 40 percent DEET or less. DEET's duration of action tends to plateau at concentrations higher than 50 percent, so relatively little additional benefit is afforded by 95 percent DEET. Given that we found a mean protection time of five hours for 23.8 percent DEET,3 adequate protection can be achieved by using products with lower concentrations and reapplying the repellent as needed.
Like Harvey, we would like the convenience of having an effective oral arthropod repellent. Unfortunately, vitamin B1 has been proved to be ineffective.4
Brownstone mentions a piperidine-based repellent, Bayer's Bayrepel. This repellent has been available in Europe since 1998 and was registered with the EPA in 2000 but is not yet available in the United States. If it proves to provide protection against mosquito bites for two to eight hours (as stated in Bayer's literature5), it may well provide repellent action similar to that of DEET.
We should have noted in our article that Dr. Day was an expert witness for S.C. Johnson, maker of OFF insect repellents, in April 2002. We apologize for the oversight.
Mark S. Fradin, M.D.
Chapel Hill Dermatology
Chapel Hill, NC 27514
mark_fradin{at}med.unc.edu
Jonathan F. Day, Ph.D.
Florida Medical Entomology Laboratory
Vero Beach, FL 32962
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