How DEET Works


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Is th­e­re anything more annoying than the ­­high-pitched buz­z of a mosquito in your ear? As you wave your arms around your head, trying to shoo the insect away, another one lands on your leg. And the next day, your memories of yesterday's picnic are dotted with red, itchy bumps.

For most of us, mosquitoes are simply a nuisance. But in some parts of the world, they're much more than that. Mosquitoes and other biting insects spread disease and cause widespread fatalities. In fact, mosquito bites result in the deaths of more than 1 million people every year [source: WHO]. The majority of these deaths are due to malaria.

Fortunately, a compound called N,N-diethyl-meta-toluamide can keep these little buggers and their diseases at bay. You might know it by its household name, DEET. DEET is found in many insect repellents. It's a man-made chemical and is proven to deter insects like mosquitoes, black flies, ticks, fleas, chiggers and no-see-ums. Repelling these insects means a significant decrease in your chances of contracting malaria, West Nile virus, Lyme disease and many other insect-borne illnesses.

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The U.S. Army developed DEET in 1946 to protect soldiers in jungles from mosquito-borne illnesses. In 1957, the government approved DEET for general public use, and today about 30 percent of the U.S. population uses DEET each year [source: NPIC]. You'll find DEET in most store-bought insect repellents -- liquid sprays, wipes, sticks and lotions. You can apply DEET directly to your skin or clothing, but you should never ingest it. When it comes to children, you should use DEET with care. Various concentrations of DEET are available, and it's not surprising to learn that repeated doses of high concentrations can be dangerous for your health.

Oddly enough, scientists aren't even completely certain why DEET works. Perhaps it prevents the mosquito from recognizing you as prey. Or perhaps it coats you with a scent mosquitoes simply find revolting. Either way, it doesn't kill the insects -- it just repels them.

DEET is not without controversy or side effects. In fact, the chemical that you slather on your skin at backyard picnics can actually melt plastic. How does that make you feel?

Do mosquitoes think DEET stinks?

Insects like mosquitoes locate us through their sense of smell, not sight. The odors­ in our sweat and breath are extremely attractive to them. Specifically, carbon dioxide, lactic acid and an alcohol-based compound called 1-octen-3-ol ar­e the main allure. The olfactory system of an insect contains odorant receptors, used to recognize the smell of prey. DEET interferes with these receptors, but scientists aren't sure exactly how. Does DEET smell bad to mosquitoes? Or does it simply make them unable to smell at all? Research results vary.

A study in 2008 showed that DEET targets certain odorant receptors in the insect, confusing its olfactory system and therefore "blinding" the bug to the odor that usually attracts it to us [source: Science Daily]. So, if this is true, DEET isn't actually a repellent. It's more like an invisibility cloak. However, a more recent study suggests that mosquitoes can actually smell DEET. A University of California Davis study showed that mosquitoes avoid DEET because they think it stinks [source: Fountain].

DEET Products

DEET is available to the consumer in various forms. In fact, the­ U.S. Environmental Protection Agency currently registers 39 companies with about 140 products containing DEET [source: EPA]. DEET products are available as liquids, lotions, sprays, and impregnated materials like wristbands or wipes. These products are all for direct application to the skin.

So how much DEET do you need to rub onto your skin to make yourself unattractive or invisible to biting insects? Currently, DEET skin application products are available in concentrations from four to 100 percent [source: EPA]. A higher concentration of DEET doesn't mean it's more effective -- it just means it lasts longer. The more DEET a product contains, the longer it will protect you from insects. For example, if you plan to do some gardening in the yard for only an hour or so, a product with 5 to 7 percent DEET should be enough. For a longer, more intense outdoor experience like fishing or hiking, 25 to 30 percent is a better choice [source: SE Johnson].

That said, the Centers for Disease Control and Prevention (CDC) states that any concentration more than 50 percent doesn't offer any added protection [source: CDC]. In fact, Canada limits all consumer DEET products to a concentration of 30 percent or less [source: Health Canada]. If you need longer protection, labels recommend that you simply reapply once the repellent stops working.

The EPA doesn't restrict DEET concentration for children, saying there's no data to suggest any negative effects [source: EPA]. However, the American Academy of Pediatrics recommends using DEET products only on children older than two months and to keep it away from their hands, eyes and mouths [source: AAP].

Many people do feel DEET is dangerous and opt not to use it on themselves or their children. We'll look at DEET side effects and controversies on the next page.

DEET Side Effects and Controversies

Jonathan Day, Ph.D, of the University of Florida Medical Entomology Laboratory, sticks his arm in a cage filled with mosquitos to demonstrate the effectiveness of repellents containing DEET.
Jonathan Day, Ph.D, of the University of Florida Medical Entomology Laboratory, sticks his arm in a cage filled with mosquitos to demonstrate the effectiveness of repellents containing DEET.

As wit­h most chemical compounds, DEET doesn't come without warnings or side effects. First, let's take a look at how DEET affects the environment.

The U.S. Environmental Protection Agency (EPA) reregistered DEET in 1998 to ensure it conformed to today's more stringent standards (rather than the 1950s standards). Because DEET is applied to the skin and not directly on plants or wildlife, its impact on the environment is minimal. However, the EPA shows DEET as slightly toxic to birds, fish and aquatic invertebrates. It's virtually nontoxic to mammals. The EPA currently rates DEET as Toxicity Category III, the second lowest of four categories -- or "slightly toxic" [source: EPA].

So, is DEET bad for you? The answer isn't totally clear. Overuse of DEET can have lethal consequences. Even so, data from 1961 to 2002 shows only eight DEET-related deaths. Three were from deliberate ingestion, two from dermal (skin) exposure and three were children receiving heavy and frequent applications of DEET [source: ATSDR]. The EPA stresses that DEET is perfectly safe when used in accordance with the directions on the label. Incorrect application can lead to health issues such as skin irritation, disorientation, dizziness and, in extreme cases, seizures or death [source: ATSDR].

You hear rumors that DEET causes cancer. This may partly be due to the fact that people confuse DEET with DDT, a known carcinogen. In truth, scientists have not established a direct link between DEET and cancer. The Centers for Disease Control and Prevention (CDC) classifies DEET as a group D carcinogen -- meaning it's not classifiable as to human carcinogenicity. In simple terms, that means that they can't say it causes cancer, but they can't say it doesn't, either.

For at-a-glance information, the activist group Beyond Pesticides keeps its own list of documented DEET health and environmental effects:

  • Cancer: Not documented
  • Endocrine Disruption: Not documented
  • Reproductive Effects: Not documented
  • Neurotoxicity: Yes
  • Kidney/Liver Damage: Yes
  • Sensitizer/Irritant: Yes
  • Birth/Developmental Defects: Yes
  • Detected in Groundwater: Yes
  • Potential Leacher: Yes
  • Toxic to Birds: Not documented
  • Toxic to Fish/Aquatic Organisms: Not documented
  • Toxic to Bees: Not documented

[source: Beyond Pesticides]

Using DEET Safely

Some researchers have even tied DEET to the mysterious Gulf War Illness suffered by ­many veterans of the 1991 war. Numerous soldiers reported symptoms­ like chronic fatigue, headaches, dizziness, loss of muscle control, memory issues, and muscle and joint pain. Studies in the mid-1990s showed that a combination of pesticides, including DEET, and an anti-nerve gas agent caused similar symptoms when tested on animals and insects [source: Waters].

That said, you're probably wondering how you can use DEET safely. DEET is an important weapon in the fight against mosquito- and tick-borne illnesses, so it's definitely got its value -- you just have to make sure you use it according to the label's directions. The U.S. Environmental Protection Agency requires companies to list precautions on their product labels. These labels provide important information on how to handle and apply the product. The following are some general guidelines about using products that contain DEET:

  • Don't use any product that has DEET and sunscreen mixed together. Unlike DEET, sunscreen requires frequent reapplication. DEET doesn't wear off as quickly as sunscreen, so you could end up with unsafe amounts of DEET on your skin.
  • Apply DEET only to exposed skin and/or clothing. Don't put DEET on skin that will be covered by clothing -- this will cause your skin to absorb the DEET.
  • Don't use DEET on any open wounds or rashes.
  • Keep DEET out of your eyes, mouth and ears.
  • Don't spray it directly on your face.
  • Avoid inhaling it.
  • Don't apply DEET near food or use it in enclosed areas.
  • Apply DEET in a thin layer -- just enough to cover your exposed skin. Avoid heavy application or oversaturation.
  • Once you return indoors, make sure you wash off the DEET with soap and water. It's especially important to do this if you plan to reapply the DEET later or the next day.

After reading all this, you might be wondering if DEET is worth the risk. But studies suggest that DEET is still the most effective insect repellent available [source: New York Times]. If you take into account diseases like malaria, West Nile or yellow fever, the benefits of DEET far outweigh the risks. But it's up to you to weigh the facts and make your own decision.

Is DEET safe for children?

A father protects his child from West Nile virus. 
A father protects his child from West Nile virus. 
Mario Villafuerte/Getty Images

Kids play outside a lot, and you don't want them coming in with­ itchy welts all over their bodies. But is it safe to cover your child's skin in DEET?

It is safe -- as long as you're careful about how you apply the chemical. When using DEET on or around children, use the following precautions:

  • Don't apply DEET to children under two months of age. Their skin can absorb too much of the chemical. Doctors believe that after two months of age, though, skin permeability is similar to an adult's [source: AAP].
  • For safety's sake, use the minimum amount possible when applying DEET to a child. This is actually a good rule of thumb for anyone using an insect repellent.
  • Insect repellents, like any chemical compound, should be stored away from children.
  • Don't let a child apply DEET -- spray it on your hands and do it for him or her. This prevents possible overuse.

If you notice an adverse reaction, it's safest to contact Poison Control for advice. You can gently wash the affected area with soap and water, and bring the insect repellent with you to the medical office.

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Sources

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