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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