How To Choose Insect Repellent

• FAQ
• Traditional Active Ingredients in Detail
• Natural Active Ingredients in Detail
• An Active Ingredient for Fabrics
• Summary

FAQ

Q: What are the key things I should look for when choosing a bug repellent?

A: Look beyond the brand name. The key information you want to find on the label is:

• the active ingredient — each has pluses and minuses that could be important to you
• the concentration (or percentage) of that ingredient used in the repellent — generally, the higher the concentration, the longer the repellent will be effective before a reapplication is necessary
• the insects targeted — particularly for effectiveness against mosquitoes and ticks.

Q: What active ingredient stays effective the longest?

A: DEET — in high concentrations (30% or higher) or when used in a controlled-release formula (which typically uses a 30%-35% concentration).

DEET (Diethyl Toluamide) is a chemical. To some people, the thought applying it their skin makes them uneasy. Yet DEET has been in use since 1957 and has been repeatedly tested for toxicity. The Centers for Disease Control and Prevention (CDC) recommends its usage and considers it safe when applied according to label instructions.

DEET is the only active repellent ingredient available currently in high concentrations in the U.S. Why? Only DEET's higher concentrations have been screened extensively for toxicity (a lengthy and expensive process, costing millions). Such data is required by the Environmental Protection Agency, which regulates repellent ingredients in the U.S. Over time, newer repellents will likely be researched more extensively and higher concentrations will become available.

In lower concentrations, active ingredients (DEET included) provide shorter-term effectiveness. The duration of effectiveness will vary by active ingredient.

For example, in an often-cited study published in the New England Journal of Medicine in 2002, DEET at 6.7% was effective for 112 minutes before the first bite was registered. Citronella at 10% yielded a bite after 19.7 minutes. A 2004 study produced similar results.

What does that mean for you? Base your choice on the amount of time you plan to spend outside. If you are planning a vigorous all-day hike, choosing a high-concentration repellent makes sense — you will have less need to reapply the repellent. If you are planning just a short walk or a casual backyard activity, you could choose a low-concentration repellent — usually effective for 1 to 4 hours.

Q: What if I'm heading into a highly bug-infested area?

A: Consider wearing clothing treated with permethrin, an insecticide engineered specifically for fabrics (such as clothing or tents). You can achieve a high level of protection by using both:

• permethrin-treated clothing (long pants, long-sleeve shirt)
• a high-concentration or controlled-release version of DEET on exposed skin.

Q: How can I best defend myself against West Nile virus and Lyme disease?

A: Here are recommendations from the CDC:

West Nile virus (carried by mosquitoes): Use repellents containing DEET, picaridin or oil of lemon eucalyptus and wear clothing treated with permethrin.

Lyme disease (carried by ticks): Use repellents containing DEET (in 20% or higher concentrations) and wear clothing treated with permethrin.

Q: Wearing repellent on my skin or permethrin-treated clothing is unappealing to me. Am I really at risk if I avoid using such measures?

A: Very likely, yes. West Nile virus has been detected in almost every state, with 4,261 cases (and 174 fatalities) reported in 2006. In 2005, 23,305 cases of Lyme disease were reported in the U.S. With West Nile virus, the number of cases continues to rise and the geographical distribution of the disease now reaches across the continental United States. In 1999, only one state (New York) had reported a human case.

In contrast, the health risks associated with repellents and permethrin, according to health authorities, range from tiny to nonexistent. This is why an agency such as the CDC advocates their use.

"Each year some areas of the U.S. experience intense outbreaks of West Nile virus transmission," says Dr. Emily Zielinkski-Gutierrez, a behavioral scientist with the CDC. "If you hear reports of human cases, infected mosquitoes or dead birds, it makes sense to raise your level of concern and take more precautions.

"Likewise with Lyme disease, if you live on the East Coast or an area of intensive transmission in the upper Midwest, the chance of getting infected is something to take very seriously.

"The risk of some mosquito- or tick-borne disease is present in nearly every state," says Zielinkski-Gutierrez. "Taking a few minutes to apply a repellent can prevent infection with a serious or life-threatening illness. That seems like a pretty reasonable trade-off to me."

Q: How about malaria and international travel?

A: Malaria, also transmitted by mosquitoes, is a serious and potentially fatal disease concern in some countries. To defend yourself against it, the CDC recommends:

• DEET (reapplied as needed, according to product instructions)
• clothing and bed-netting treated with permethrin
• taking a preventative antimalarial drug.

The species of mosquito that transmits malaria is more aggressive than North American species, meaning you may need to reapply repellent more often than you would back at home.

Other mosquito-transmitted diseases include yellow fever (for which a vaccine is available; it is required for entry into some countries), dengue fever and Japanese encephalitis, making repellent an important travel accessory. Check for airlines restrictions regarding aerosol containers. For info on your travel location, visit www.cdc.gov/travel.

Q: What are my choices of active ingredients?

Traditional (DEET, Picaridin, IR 3535)	Natural (Plant-based formulas)
Pros Most effective; longer lasting Long record of safety	Pros Derived principally from plants Won't damage fabrics or surfaces
Cons Chemical-based DEET may impact fabrics or surfaces IR 3535 may impact plastics	Cons Variable duration of effectiveness Reapplications usually needed

Traditional Active Ingredients in Detail

DEET (N,N-diethyl-3-methylbenzamide, or N,N-diethyl-m-toluamide)

Pros:

• Globally regarded as the gold standard of repellents
• Developed for military use in 1946; approved for public use in 1957.
• Regarded as the longest-lasting, most effective active ingredient in the insect-repellent arsenal; some formulas provide up to 12 hours of protection.
• Used safely by humans in small or moderate amounts for 5 decades; has been the subject of numerous studies since its introduction.
• According to the American Academy of Pediatrics, suitable for children at least 2 months old in concentrations of up to 30% when used according to directions on product labels.

Cons:

• DEET is a "plasticizer." It can have adverse affects on most synthetic fabrics (such as rayon or spandex), auto paint, watch crystals, varnished surfaces, golf-club grips, leather and plastic. It will not damage cotton, wool or nylon.
• A potentially objectionable odor.
• Less effective against some flies. For problematic flies, consider repellents that use:
  • picaridin
  • IR 3535
  • DEET combined with a fly-targeted ingredient such as R-326).

Picaridin (KBR 3023)

Pros:

• Developed in Europe in 1998; approved for use in U.S. in 2005.
• Effective against mosquitoes and ticks; more effective against flies than DEET.
• Causes no damage after contact with synthetic fabrics or painted/varnished surfaces.

Cons:

• Currently available only in lower concentrations (starting at 5.75%; a 20% version will be available soon).
• Duration of effectiveness is fair to good (3 to 8 hours).

IR 3535 (3-(N-butyl-N-acetyl)-aminopropionic acid ethyl ester)

Pros:

• Used in U.S. since 1999.
• Moderately effective against mosquitoes, ticks and flies; potentially may also repel bees and wasps.
• Registered as a biopesticide with EPA.
• Exhibits lower toxicity as compared to some other active ingredients.

Cons:

• Some researchers consider its duration of effectiveness as unpredictable.
• Can damage plastics.

Natural Active Ingredients in Detail

Oil of Lemon Eucalyptus (natural oil is extracted lemon eucalyptus leaves and twigs)

Pros:

• Used in the U.S. since 2000.
• Effective against mosquitoes, ticks and some flies.
• Causes no damage after contact with synthetic fabrics or material surfaces.

Cons:

• A strong, distirnctive odor.
• Label instructions advise applying it to skin no more than twice a day; may irritate some sensitive skin.
• Duration of effectiveness is fair (up to 4 hours)

Citronella (natural oil is derived from dried cultivated grasses)

Pros:

• Used in the U.S. since 1948.
• Effective against mosquitoes, ticks and some flies.

Cons:

• A potentially objectionable odor.
• May irritate some sensitive skin.
• A faint risk to stain some fabrics.
• Duration of effectiveness is low to good (1 to 6 hours).

Herb-based formulas (ingredients range from soybeans to crushed chrysanthemums)

Pros:

• Effective against mosquitoes and ticks.
• In some cases, a less objectionable odor.

Cons:

• Duration of effectiveness is unpredictable.

An Active Ingredient for Fabrics

Permethrin (a chemical insecticide; applied to clothing either by soaking or spraying)

Pros:

• Used in the U.S. since 1979.
• Effective against ticks, mosquitoes, mites and up to 50 other insects.
• Application can last up to 6 washings and for 6 weeks.
• Won't stain fabrics; almost never irritates skin.
• Considered to be biodegradable; shown to not accumulate in the environment.
• In some circumstances may preclude the use of topical repellents, especially if ticks are the main concern.
• Repels insects; kills insects that contact the treated clothing and bed-netting.

Cons:

• Care is needed to avoid flushing permethrin in liquid form into a sewer system or water supply. Once dry, however, there is no risk.

Tip: Plan ahead. Apply permethrin to fabric well in advance of a trip and allow it to fully dry before wearing or using it.

Q: How safe is DEET?

• Lab tests have shown that skin absorbs DEET, but is eliminated from the body through urine (the highest concentrations being expelled several hours after application).
• Human and animal studies indicate that DEET does not accumulate in the body.
• DEET-related illnesses have been reported in medical literature, but typically because DEET was used inappropriately, excessively and/or over a prolonged time.
• Some medical professionals wonder about chemical exposure and a child's brain development. One study using rats indicated DEET produced a neurological effect; several other studies showed no neurological link.
• No repellent, DEET-based or otherwise, should be applied close to the eyes or on broken skin.

Note: DEET and all active ingredients described in this article are registered with the Environmental Protection Agency (EPA). They have been evaluated for safety and, in most cases, efficacy when used according to label instructions. This is a key in appropriate use of insect repellents: Follow label instructions.

Q: Can children safely use DEET and other repellents?

A: According to the CDC: "No definitive studies exist in the scientific literature about what concentration of DEET is safe for children. No serious illness has been linked to the use of DEET in children when used according to manufacturer's recommendations."

Pediatricians typically suggest avoiding the use of repellents on infants younger than 2 months and advise DEET concentrations up to 30 percent. Repellents containing oil of lemon eucalyptus often carry a label warning that they should not be used on children under the age of 3.

Q: Can insect repellent and sunscreen be worn at the same time?

A: Little hard evidence on this topic exists, though it is generally accepted that applying both insect repellent and sunscreen topically (to the skin) will diminish the efficacy of both.

Our advice: Generously apply sunscreen to cool, dry skin 20 to 30 minutes before activity. Wait until insect activity demands repellent, then apply it. A few sunscreen/repellent combos exist.

Q: What do we know about mosquitoes?

A: Here are some interesting facts provided by the nonprofit American Mosquito Control Association:

• There are about 2,700 species of mosquito. There are 176 species in the United States. Texas has the most species (85), West Virginia the fewest (26).
• The average mosquito weighs about 2.5 milligrams.
• Mosquitoes fly an estimated 1 to 1.5 miles per hour.
• Only female mosquitoes feed on blood (it helps their eggs mature).
• The average mosquito takes in about 5-millionths of a liter of blood during feeding.
• Mosquitoes find hosts by sight (they observe movement); by detecting infrared radiation emitted by warm bodies; and by chemical signals (mosquitoes are attracted to carbon dioxide and lactic acid, among other chemicals) at distances of 25 to 35 meters.
• Bigger people are often more attractive to mosquitoes because they are larger targets and they produce more mosquito attractants, namely carbon dioxide (or CO₂, released mainly from the breath, but also the skin) and lactic acid.
• Active or fidgety people also produce more CO₂ and lactic acid.
• In general, adults are more likely to be bitten than children, although adults may become less attractive to mosquitoes as they age.
• Women are usually more attractive to mosquitoes than men because of the difference in hormones produced by the sexes.
• Blondes tend to be more attractive to mosquitoes than brunettes.
• Smelly feet are attractive to mosquitoes — as is Limburger cheese.
• Dark clothing attracts mosquitoes.
• Movement increased mosquito biting up to 50% in some research tests.
• A full moon increased mosquito activity 500% in one study

Q: How do repellents work?

A: Active ingredients in repellents create a vapor barrier at the skin surface that disorients or inhibits mosquitoes. Mosquitoes have chemoreceptors on their antennae that are stimulated by carbon dioxide or lactic acid. These same receptors, it appears, are inhibited by active ingredients such as DEET.

Wearing repellent underneath clothing almost always reduces the efficacy of repellent, since clothing interferes with the vapor barrier repellents attempt to create on skin surfaces.

Q: Should I use lotions or sprays?

A: Sprays may allow active ingredients to evaporate faster than lotions, reducing the duration of their effectiveness. Sprays, though, can be useful when spraying repellents on clothing (if insects are biting you through your shirt, for example). Remember, however, that DEET (but not picaridin) can damage most synthetic fabrics. DEET does not damage cotton, wool or nylon.

Alcohol-based sprays tend to cause skin pores to open wider, possibly allowing more the body to absorb more of the repellent's active ingredient. This may not appeal to those who use a traditional (chemical-based) repellent. Water-based sprays do not have the same effect.

Summary

• When choosing a repellent, look for its 1) active ingredient and 2) the concentration of that ingredient. Higher concentrations (or controlled-release formulas) last longer.
• DEET, used since 1957, is viewed as the most effective, longest-lasting ingredient available; other options (including natural ones) are also effective, but for shorter durations.
• Studies have shown no evidence that occasionally absorbing small amounts of DEET (which is eliminated from the body within 24 hours through urine) has harmful effects on humans.
• A combination of permethrin-treated clothing and topical repellents offers your most comprehensive package of defense against insects (including those that transmit West Nile virus and Lyme disease).
• Children older than 2 months can safely use repellents with active ingredients in concentrations of up to 30 percent.