Is Permethrin-Treated Clothing Safe and Effective?

    The pesticide can be useful in preventing tick bites, but it has potential risks, too

    family hiking in the woods Photo: Tom Werner/Getty Images

    Wearing clothing treated with permethrin is one of several strategies recommended by public health experts to prevent bites from ticks and mosquitoes.

    But—at least when it comes to protection against ticks—it appears to be used less often than other measures, such as skin-applied repellents and tick checks, according to a recent analysis by the Centers for Disease Control & Prevention (CDC).

    People may not be as familiar with using permethrin to prevent tick and mosquito bites as they are with popular bug sprays that contain active ingredients like deet or picaridin. Unlike skin-applied bug repellents, which simply ward off bugs so they don’t bite you, permethrin can also disable or kill bugs on contact. 

    It’s also different in another critical way: You don’t apply it to your skin—ever. Doing so would be dangerous. Instead, it can be sprayed onto clothing, shoes, and gear. Consumers can also send clothing through the mail to be commercially treated by a company like InsectShield, or buy clothing that’s been pre-treated with permethrin. 

    Here, what we know about permethrin’s efficacy against ticks, its risks and drawbacks, potential safety concerns, and what you need to know about using it.

    Why You Should Consider Permethrin

    While permethrin-treated clothing can be used to protect you against both mosquitoes and ticks, evidence suggests permethrin may be particularly useful in preventing tick bites. Studies conducted among outdoor workers show significant reductions in tick bites among workers who used permethrin-treated clothes.

    more on preventing bug bites

    In one study published in 2020 in the Journal of Medical Entomology, researchers recruited outdoor workers to have some of their work clothes commercially treated with permethrin (the control group’s clothing was left untreated). In the first year of the study, workers wearing the treated clothing experienced 65 percent fewer tick bites than workers who didn’t have treated clothes.

    In the second year, as the permethrin presumably began to wear off, workers wearing treated clothing still experienced 50 percent fewer tick bites.

    That’s not perfect protection, but overall it’s a good result—especially for workers exposed to ticks for hours every day, says Thomas Mather, PhD, director of the University of Rhode Island’s Center for Vector-Borne Disease and one of the authors of the study. 

    Plus, “it might be more effective for the consumer than the outdoor worker only because their exposure level is probably a lot less,” says Mather. “It’d be great if it worked all of the time, but if it works enough, that’s also good.”

    One advantage of permethrin is that it’s longer lasting than skin-applied bug sprays. That may be particularly useful for people trying to avoid ticks.

    When mosquitoes are your main concern, you can tell when an insect repellent is wearing off because mosquitoes will start biting again (that’s a sign to reapply). Ticks are more stealthy, and you often won’t feel it when they bite. That’s one reason it’s helpful that permethrin is designed to last for days or weeks, rather than hours. 

    Potential Permethrin Downsides

    A key downside of permethrin is that it can’t be used directly on skin, so if, for instance, you want to wear shorts when you go hiking in tick territory, you’ll still need to apply bug spray to your exposed skin.

    And if mosquitoes are your main concern, you may be better off with deet: In a 2016 test, CR found that a shirt sprayed with deet kept mosquitoes at bay better than clothing professionally treated with permethrin.

    Permethrin’s efficacy also wanes over time as it washes and wears out of your clothes. A 2019 study in the Journal of Medical Entomology found significant reductions in the amount of permethrin remaining in professionally treated clothes after 16 rounds of washing and drying over an eight-week period. That didn’t mean it no longer worked, however.

    “Even with a loss of permethrin, we found that the treated clothing still was quite effective at repelling ticks,” says study author Neeta Connally, PhD, a professor of biology and principal investigator of the Tickborne Disease Prevention Lab at Western Connecticut State University. “This suggested to us that wearing [professionally] permethrin-treated clothing even after several launderings still offers some protection from ticks.”

    Still, retreatment of clothing is wise. If you live in a tick-heavy area, you may want to treat or retreat your clothes just before the height of tick season in your area. In places where blacklegged ticks, which cause Lyme disease, are common, peak tick season starts around May. People can encounter ticks at many other times during the year, however, Connally cautions. (Blacklegged ticks, for instance, can be active through the winter, if temperatures are above freezing and the ground isn’t covered in snow.) 

    The best and longest-lasting efficacy will likely come from clothing treated professionally, says Mather. When you treat your own clothing at home, you may not coat garments adequately, and the permethrin washes out more quickly.

    Permethrin Safety Considerations

    Permethrin is a pesticide in a class known as pyrethroids, and research suggests it has some potential health risks.

    A 2019 study that followed more than 2,000 adults over 14 years found that people with higher exposure to pyrethroids had an increased risk of dying from heart disease. (The study involved a small number of people, however, and couldn’t establish whether pyrethroids caused the deaths or whether another factor was to blame.) 

    Like many other pesticides, permethrin has also been implicated as a possible endocrine disruptor, notes CR’s senior scientist, Michael Hansen, PhD. Endocrine disruptors mimic or block the activity of your hormones, which can have effects all throughout the body and brain.

    Research suggests that permethrin can be found in the blood and urine of workers who wear treated clothing, which means it can be absorbed from clothes into the body. In one 2019 study, the levels of permethrin found in the urine of workers was well below both Environmental Protection Agency and World Health Organization limits for safe exposure to the chemical.

    But endocrine disrupting chemicals have the potential to cause harm at much lower doses than the legal limits, Hansen cautions. Young children and people who are pregnant may be most at risk from endocrine disruptors, so for people in these groups, thinking carefully about minimizing exposure (for instance, by using treated clothing infrequently or only in the highest-risk situations) is wise.

    Ultimately, you’ll need to weigh the possible health risks of permethrin against the risk of contracting a tick-borne disease, many of which can have serious, long-lasting health consequences

    If you opt to treat your clothes yourself, additional safety measures are needed. First, make sure you are using spray formulated specifically for clothing; do not buy or use agricultural-grade permethrin, even if you dilute it. 

    Second, never spray when you are wearing the clothing you want to treat; clothing must be sprayed and then dry completely before you wear it. Permethrin should also never be sprayed around cats, for whom it is highly toxic. (See these tips on using permethrin safely.)

    Permethrin is not your only option for protection. Simple adjustments can make a big difference, public health experts say, such as wearing light-colored long pants and sleeves when you’re out in tick habitat, tucking in your shirt, pulling your socks up over your pants, and—when you return home—performing tick checks and taking a shower.

    You can also consider insect repellents that contain deet, picaridin, and oil of lemon eucalyptus, all of which are registered by the EPA for protection against ticks. 

    Catherine Roberts

    As a science journalist, my goal is to empower consumers to make informed decisions about health products, practices, and treatments. I aim to investigate what works, what doesn't, and what may be causing actual harm when it comes to people's health. As a civilian, my passions include science fiction, running, Queens, and my cat. Follow me on Twitter: @catharob