Is DEET Safe?

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More than 72 years after its development, N,N-diethyl-meta-toluamide, or DEET, remains the most widely used topical insect repellant in the world. As of 2009, it had been applied 8 billion times worldwide, and 200 million people rely on the chemical to keep them safe from mosquito and tick bites every year. Yet the internet is rife with questions over its safety for humans and animals.

Multiple readers have asked me: Is DEET something we should feel okay about applying to our skin? Let’s find out.

Any DEET-based insect repellant container will be swathed in prominent warning labels. That’s because lots of studies have found DEET to be harmful to people and the environment. Here are just a few examples:

• A study conducted on wastewater-polluted streams in the continental United States found DEET in 73 percent of the stream sites sampled, suggesting that DEET can move into the environment through wastewater treatment facilities.
• A study conducted by the American Association of Poison Control Centers between 1993 and 1997 analyzed 20,764 exposures to DEET that were reported to poison control. It found two deaths among that group that could be related to the chemical.
• The Journal of Environmental Biology released a report in 1989 indicating that DEET could build up in the organs of freshwater fish over time, potentially accumulating to lethal doses.
• The U.S. Department of Health and Human Services Agency for Toxic Substances and Disease Registry reports eight DEET-related deaths between 1961 and 2002. Three were the result of deliberate ingestion, two were caused by skin exposure in adults, and three were children who were administered very heavy and frequent doses of the substance.
• Research published by Duke University in 2000 reports that dermal exposure to DEET resulted in “oxidative DNA damage,” even at relatively minimal dosage levels. “The results indicate that dermal administration of DEET could generate free-radical species,” the scientists reported, referring to the chemical’s ability to damage DNA.
• The Research Advisory Committee on Gulf War Veterans’ Illnesses concluded in 2008 that “evidence strongly and consistently indicates” that DEET, combined with pyridostigmine bromide pills (administered to counter the effects of nerve agents), created effects correlated with the mysterious illness called Gulf War Syndrome.
• Perhaps most convincingly, the National Park Service studied the effects of DEET on employees in Florida’s Everglades National Park, who use large quantities of the substance on a daily basis. Using both voluntary answers and urinalysis, it found a correlation between heavy DEET exposure and insomnia, muscle cramps, and “urinary hesitation.”

The Environmental Protection Agency recertified DEET in 2014 as part of a regular evaluation process that looks at current science to make sure pesticides remain safe. The EPA noted the reported cases of DEET-related incidents yet moved forward with the certification anyway. Why? “The number of incidents is relatively small when compared to the number of users,” the report states. “It is important to note, however, that there are a large number of users of DEET and the number of incidents is relatively small in comparison.” Between 1984 and 1989, the EPA reported that 104 million people in the United States used DEET to protect them from biting insects. During that time, it found only 387 health incidents related to the chemical and no deaths that could be attributed to it.

I wanted to put that exposure-to-risk ratio in perspective by comparing it to other common substances. Acetaminophen was my first idea since I took two Tylenol this morning. About 27 billion acetaminophen doses are sold in the United States each year, and it’s estimated that 110,000 health incidents result from that drug and around 300 annual deaths. ProPublica therefore estimates that there’s one injury per 100,000 doses, if all doses are consumed in the year that they’re sold. That makes using DEET about three times safer than using Tylenol, according to this data.

It’s also impossible to talk about the risks of DEET without discussing the dangers it helps prevent. Between 2004 and 2016, the Centers for Disease Control and Prevention reported more than 640,000 cases of human illness caused by mosquito, tick, and flea bites. That rate has tripled in 13 years. In its report, the CDC suggests that you employ an insect repellant and suggests a list of repellants that includes DEET.

As for the risks DEET posed to the environment, those seem to be a case of people comparing the results of two studies—its prevalence in wastewater-polluted streams and its low-level toxicity to fish—without diving deep into the numbers.

Take the study I linked to above, which reported that DEET was found in 73 percent of all U.S. streams. It surveyed only 56 streams in the United States, and most were downstream from a major urban area, meaning they had a high likelihood of being polluted by wastewater. If you look at the map of results, streams in rural areas look like they’re less likely to contain DEET than those near cities. Rural Idaho, for instance, shows three streams that are free of DEET, while California shows three that contain it and one in the less-populated northern portion of the state that doesn’t.

There’s also a disparity between the levels of DEET detected in that study (the highest concentration found was 1.1 μg/L) and the concentration necessary to harm fish, which is 75,000 times greater than that highest amount. The World Aquaculture Society considers the concentration of DEET required to harm fish so high that it’s “to be considered practically nontoxic.”

The Center for Biological Diversity agrees with the EPA’s recertification findings that DEET does not pose a risk to any endangered species.

“Currently available non-DEET repellents do not provide protection for durations similar to those of DEET-based repellents and cannot be relied on to provide prolonged protection in environments where mosquito-borne diseases are a substantial threat,” concluded a landmark study published by the New England Journal of Medicine in 2002. In it, the purported efficacy of products like Avon Skin So Soft, citronella oil, soybean oil, and other natural remedies was disproven.

But since that time, a new repellant called picaridin has been certified for use in the United States. Studies have found it to be as effective at DEET and with fewer reports of health incidents. Additionally, picaridin does not melt plastic, nor does it feel oily on skin. It’s worth noting that usage levels of picaridin remain lower than DEET and the substance has not been studied nearly as much. The negative health effects of DEET have been shown to be infinitesimal over billions of uses and a human lifetime of use. To categorically state that picaridin is safer would take a study of equivalent duration and prevalence, and any findings would be splitting hairs, but it does seem to be a viable option.

Of course, there are other ways to repel insects without the use of topical repellents. Clothing treated with permethrin is effective at deterring both ticks and mosquitoes (although that substance has been found to be toxic to cats), and heating allethrin-soaked pads can make a small outdoor area totally free of mosquitoes—Thermacell has a variety of options. And you can always use a mosquito net to protect your sleeping area at night or as an alternative to applying chemicals to an infant.

If you’re concerned about the safety of DEET, the best advice comes from the CDC: “Using insect repellents containing DEET should not be harmful if label directions are followed.” Most reported problems with DEET come from either ingestion or extreme overapplication. Avoid drinking DEET or coating yourself in high concentrations of it multiple times a day, and you should be fine.