What’s the Buzz on Insect Repellents?

by Yael Resnick

Although there is a real health threat to humans and animals from mosquito-borne illnesses such as West Nile Virus, encephalitis, malaria, and yellow fever, must we resort to toxic chemicals?

Every year, the Centers for Disease Control puts out its official government recommendation for how we should keep mosquitoes from biting us and our children. As usual, the CDC recommends conventional repellents containing potentially harmful chemicals.

This year, their recommendation is to use an insect repellent that contains one of three ingredients approved by the Environmental Protection Agency for use on clothing and skin:

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

2)    picaridin (chemical name KBR 3023)

3)    oil of lemon eucalyptus (chemical name p-menthane 3,8-diol, or PMD)

In most messages boiled down for consumption for the general public, DEET is the only ingredient recommended. For example, in the CDC’s document entitled, “Five Common Myths About West Nile Virus,” they state: “Make a habit of using insect repellent with DEET when outdoors.” When you dig deeper into the CDC’s online data (at www.cdc.gov), you do find the other approved ingredients listed as well, and a CDC spokesman was quoted on WebMD saying that for backyard use, picaridin or lemon eucalyptus oil are fine, but he would recommend DEET for people who will be camping, for example. Detailed fact sheets about all of the recommended repellents are posted; you can find them if you search.

Is DEET Safe?

The use of DEET brings risks to human health and the environment that are completely avoidable.

The American Academy of Pediatrics’ Committee on Environmental Health also releases their official opinion about repellents. They have not commented about picaridin or oil of lemon eucalyptus, but they have this to say about the use of DEET on children: "Insect repellents containing DEET…with a concentration of 10% appear to be as safe as products with a concentration of 30% when used according to the directions on the product labels." The AAP advises that repellents with DEET should not be used on infants less than 2 months old.

The fact sheets published by the CDC to “educate” consumers about DEET are notable for what they don’t tell us. Comparing these public information sheets to the reports of actual research studies about the safety of DEET is an eye-opening exercise. These reports are all available online at CDC’s website, but you have to know what you are looking for and search for it specifically, and then you have to read the “technical” stuff.

Here’s what it says on their Division of Parasitic Diseases’ “Fact Sheet for the General Public” about the safety of DEET:

“Can DEET cause health problems? Using insect repellents containing DEET should not be harmful if label directions are followed and the product is used safely. In rare cases, using DEET products may cause skin rashes. Some persons who used products containing a high concentration of DEET or who were exposed to excessive amounts of DEET have experienced skin rashes, blisters, and skin and mucous membrane irritation.” 

The “fine print” about the safety of DEET can be found in reports of the chemical technical studies intended for “public health and public safety professionals.” There you find out that DEET has been associated with toxic effects ranging from mild skin irritation to death. The most severe cases are rare fatal episodes of intentional ingestion, and several unusual cases in which young children died after being treated with heavy applications of DEET on a frequent or daily basis. There have also been cases of severe psychological disturbance, including hallucinations and delusions, as a result of the use of DEET.

There have been reports of serious skin lesions caused by DEET—specifically, in people who slept with DEET applied to their arms at the fold of the elbow. In controlled studies conducted on soldiers to follow up on these isolated cases, it was found that the inside of the elbow (but not the upper arm) was reactive to DEET in almost half of the subjects. Some of the soldiers required medical treatment, had permanent scarring, or needed corrective cosmetic surgery.

A study of 143 National Park Service workers found that DEET commonly causes a wide variety of health problems. One quarter of those who had moderate to high exposure to DEET reported health effects they attributed to the chemical, including rashes, skin or mucous membrane irritation, transient numb or burning lips, dizziness, disorientation, difficulty concentrating, headache, and nausea.

Data from calls to poison control centers have been analyzed in several studies. Most of the DEET-related calls were about accidentally getting DEET in the eyes, or about minor skin irritations. But about 1.5 percent of the calls reported neurological symptoms, including dizziness, headache, drowsiness, lethargy, tremors, involuntary movements, seizures, and convulsions. Serious effects, including death, have been reported when children have been exposed to excessive amounts of DEET on their skin (for example, daily for three months) or by accidental ingestion.

In order to help people guard against the negative effects of DEET, the CDC offers a laundry list of safety precautions, including the following:

• Read and follow all directions and precautions on the product label.

• Store DEET out of reach of children.

• Use only when outdoors and wash skin with soap and water after coming indoors. This is particularly important when repellents are used repeatedly in a day or on consecutive days.

• Use just enough repellent to cover exposed skin and/or clothing. Avoid over-application of the product. (In some publications, the caution is simply to apply DEET “sparingly”.)

• Do not allow children under 10 years of age to apply repellent themselves.

• Do not apply to young children’s hands or around eyes and mouth.

• Do not apply repellent under clothing. If repellent is applied to clothing, wash treated clothing before wearing again.

• Do not breathe in, swallow, or get into the eyes. DEET is toxic if swallowed.

• If you or your child get a rash or other bad reaction from an insect repellent, stop using the repellent, wash the repellent off with mild soap and water, and call a local poison control center for further guidance.

• If you go to a doctor because of the repellent, take the repellent with you to show the doctor.

I find it rather interesting that on one hand, we as consumers are told that DEET is “safe,” and on the other hand, DEET is clearly known to be a poison with a long string of toxic effects. (It’s interesting that products containing oil of lemon eucalyptus are labeled with a caution not to use them on children under 3 years old. However, the CDC’s fact sheet on oil of lemon eucalyptus states that it “shows no adverse effects except for eye irritation.”)

Although the CDC’s consumer guidelines for “safe” use of DEET are given with good intentions, they seem to be based on overly optimistic assumptions about how parents and children may really use these products. The reality is that children are likely to apply repellent themselves (think of kids at camp spraying each other’s arms before a hike); products are not always easy to apply sparingly, and the term “sparingly” itself is open to interpretation; and children cannot be counted on to wash their skin and clothing when they come in from outdoors—and so their exposure to the chemical repellent is likely to be prolonged.

Also important to note: a higher percentage of DEET in a product does not mean that the product is more effective, only that it lasts longer. In light of that, I find it disconcerting that children are advised to use products with lower concentrations of DEET, and to use such products sparingly in order to minimize exposure, when in practice, the product will in fact need to be reapplied in order to maintain its effectiveness—thus increasing the child’s exposure to the chemical.

It’s not surprising, but still rather disturbing, that consumers are not told the whole story about DEET’s health effects. No wonder the CDC says that 30% of people in the U.S. use DEET. Most people don’t know they have other effective—and safe—alternatives. For me, personally, any chemical that comes with so many warnings is something I wouldn’t expose my children to at all; an intentional small dose of poison doesn’t seem justifiable when there are other options.

What is Picaridin?

What about number two on the registered repellent list: picaridin? This is a newer repellent, registered just five years ago, and so far it seems to have a pretty clean safety record. According the EPA’s fact sheet, it has been classified as “not likely to be a human carcinogen.” It has low toxicity ratings for humans. In the environment, it is not toxic to birds, but is moderately toxic to freshwater fish. It’s important to note that toxicity studies determine “acute toxicity” only—not long-term health effects.

What is Oil of Lemon Eucalyptus?

At first glance, it appears that the CDC is recommending a natural product, oil of eucalyptus, as one of the official options, but that’s only partially true. They’re not talking about “pure” oil of lemon eucalyptus—the essential oil, naturally derived from eucalyptus leaves and twigs—but rather commercial repellents containing a chemically synthesized active ingredient. This is because the essential oil was not tested for effectiveness in official studies; however, products containing synthetic oil of lemon eucalyptus were tested and found to be as effective as repellents containing the lower concentrations of DEET. Oil of lemon eucalyptus is registered as a biopesticide—in other words, it is derived from plants and poses no risk to the environment.

More Poison

Another chemical to stay away from is permethrin, which is both a repellent and a pesticide (it both repels and kills insects). Since it is not approved for use directly on skin, it is not on the CDC’s list of registered repellents. However, they do endorse permethrin for use on clothing, despite the fact that this toxic chemical will likely be in close contact with skin for prolonged periods, since clothes touch the skin. Some manufacturers of outdoor clothing (including L.L. Bean) have recently unveiled a line of clothes pre-treated with permethrin that lasts through repeated laundering. This seems like major overkill in the battle against mosquitoes and other pests for most consumers. Permethrin is a common pesticide used on crops and in homes—and is a known carcinogen, neurotoxin, and immune system disruptor. Even worse, the health risks posed by DEET are multiplied when a person is exposed to permethrin at the same time.

What Are the Alternatives?

What about all those natural repellents you see lining the shelves of your local health food store, and sold on websites and by your local Avon lady? Do they work? There aren’t any readily available studies, but many people have used them with great success.

Many essential oils are very effective insect repellents.

Besides oil of lemon eucalyptus, natural options for repelling insects are oil of citronella, cedar, lavender, garlic, cinnamon, and peppermint. The CDC will not recommend these because, while they may well be effective, they have not been as thoroughly studied as the chemical repellents, and their effectiveness may not last as long as chemicals.

It’s important to remember that natural repellents—like chemical ones—should be used with appropriate caution, since essential oils have potent medicinal effects and can be eye, skin, and mucous membrane irritants. 

Despite the insistence by the CDC that DEET is safe when used as directed, playing it safe with gentle, natural approaches to repelling insects sounds smart to me. Having the effectiveness wear off a little sooner sounds like a reasonable trade-off for better health and a cleaner environment.