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Frequently Asked Questions


How do insect repellents work?

Biting insects have antennae that detect lactic acid, carbon dioxide, and other volatile compounds that humans and animals give off in their breath and from their skin. Mosquitoes are so sensitive to these chemicals that they can detect a potential blood meal from as far away as 100 feet! Insect repellents are believed to work by blocking the stimulation of these receptors, preventing insects from homing in on their source.

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Why do almost all insect repellents contain the chemical DEET?

DEET has been used by the U.S. public since 1957. Despite 40 years of testing more than 20,000 other compounds since then, DEET remains the most-effective and broad-spectrum repellent currently available.

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I've noticed that stores sell DEET in concentrations of anywhere from 5% to 100%. How do I know which strength is right for me?

There is no one right answer to this question. The various concentrations of DEET are out there to address different needs. As a general rule, higher concentrations of DEET will offer longer-lasting protection, but this effect tends to level out at concentrations of DEET over 30%. Under most circumstances of casual use, 10% - 35% DEET will provide adequate protection. However, there are certain conditions in which using a higher concentration of DEET may be preferable. These circumstances include the following:

  • Conditions in which there is a rapid loss of repellent to the skin due to washoff from rain, perspiration, or high ambient temperatures
  • When traveling to an area where there is a very high density of biting insects (e.g., the Everglades or Alaska)
  • When traveling to areas where insect bites can transmit serious diseases to humans (e.g., malaria, yellow fever, filariasis, viral encephalitus, etc.)

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I've heard recently about "time-release" DEET repellents. Do these products have any advantages over the other DEET repellents?

Nearly all DEET-based repellents on the market contain the DEET chemical simply mixed in a base of lotion, or alcohol. Extended or time-released products, in contrast, package the DEET in a special base that allows it to be released more slowly on to the skin surface. There are several advantages to this technology: These products will give longer-lasting protection, without requiring the use of high concentrations of DEET. They also reduce the number of times that re-application of the product may be necessary. Ultrathon, which is a time-release product, contains 34.34% DEET in a polymer base; it is identical to the repellent used by the U.S. military.

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How much repellent should I apply?

Insect repellent should be applied as a thin layer, covering all the exposed skin surface evenly. There is no need to saturate the skin in order for the repellent to be effective. Do not apply insect repellent over cuts, wounds, or inflamed or eczematous skin.

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Is it O.K. to spray DEET on my clothes?

DEET can be applied to either exposed skin or clothing. It should not be applied to skin that is covered by clothes. DEET should also not be applied to synthetic fabrics such as rayon or to plastics, because it can damage these products.

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I purchased DEET-based wristbands, which claimed that they would repel mosquitoes, but they don't seem to work. Why?

DEET essentially only protects the areas to which it is applied. Its repellent effect cannot travel far. The application of DEET to a few points of the body, therefore, will not "cloak" the user in protection. All exposed skin must be treated with DEET in order for it to be protected. Hungry insects will readily find any areas of unprotected skin.

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I'm going to Africa. Which repellent should I bring with me?

When traveling to areas of the world where insect-transmitted diseases such as malaria, yellow fever and viral encephalitis are common, proper application of insect repellent is crucial to prevent the possibility of being infected. A DEET-based repellent will offer the best insurance against being bitten. Controlled-release DEET products may well be the ideal choice for the traveler looking for long-lasting protection without having to resort to using repellents with DEET concentrations over 35%. In general, citronella-based repellents would not be predicted to provide adequate protection when traveling to these areas.

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I've heard that DEET can cause seizures and neurological damage. Is that true?

Although it is true that there have been rare reports of seizures and neurological side effects associated with DEET use, it is important to realize how rare these reports are. The U.S. EPA estimates that 200 million people use DEET repellent every year. After more than eight billion applications of DEET worldwide, there have been only 21 cases reported in the medical literature in which the use of DEET seemed to have been associated with the development of neurological toxicity. Six of these cases were a direct result of deliberate ingestion. Twelve of these 21 cases resolved completely, without any residual effects. When the EPA reviewed all available DEET human and animal neurotoxicity data in 1998, they concluded there was no evidence that DEET was a selective neurotoxin. Even if all the reported cases of neurological toxicity ascribed to DEET use were confirmed, the real-life risk of neurological side effects from DEET would be less than 1 in 100 million users.

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I don't want to get a sunburn, and I want to protect myself from insect bites, too. Can I apply both sunscreen and insect repellent to my skin?

Sunscreens and insect repellents may be used together on exposed skin. However, there is some evidence that DEET can reduce the efficacy of sunscreen when applied to the same area. One study showed as much as a 33% decrease in sun protection (SPF) when a 33% DEET lotion was simultaneously applied. Therefore, when applying both DEET repellent and a sunscreen, you will need to reapply the sunscreen more frequently to prevent sunburning.

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Aren't the "natural" repellents just as good as DEET?

Currently available "natural" or "plant-based" insect repellents cannot match the broad-spectrum efficacy and long-lasting action of DEET repellents. Most natural repellents contain citronella, which is a lemony-scented oil derived from two cultivated grasses. Very variable efficacy has been reported in scientific studies of citronella, depending on the product tested and the species of insect examined. In general, these studies show very short protection times, lasting just a few minutes to up to two hours.

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I'd prefer not to apply ANY repellents to my skin. Are there other ways to avoid insect bites?

Densely woven or mesh clothing can reduce the likelihood of being bitten. As a sole method of protection, however, physical barriers have their drawbacks, including that they tend to be hot, limit mobility and visibility, and will not be effective in any area of the body where twisting or bending brings the fabric in direct contact with the skin surface, making it possible for an insect to bite through the fabric.

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Related Links
> Centers for Disease Control
> EPA Deet Information