Public health experts are increasingly concerned about the Zika virus. To combat that threat, the Centers for Disease Control and Prevention recommends a full array of anti-mosquito measures, especially for people living in or traveling to parts of South America or the Caribbean, including Puerto Rico.

Those steps include applying insect repellents, with ingredients such as deet or picaridin, to exposed skin and clothing. But another option recommended by the CDC is to wear clothing that has been treated with the insecticide permethrin.

These clothes—including shirts, pants, and hats—are made by several manufacturers, notably Insect Shield and Burlington, and are sold by brands such as L.L.Bean and ExOfficio. Sales of permethrin-treated clothes have jumped in recent months, as health officials around the world struggle to protect vulnerable populations from Zika-carrying mosquitoes.

That’s especially worrisome for women who are, or may become, pregnant, because the Zika virus has been linked to microcephaly and other the serious birth defects. Insect Shield has even launched a new lifestyle and maternity collection and tells Consumer Reports that requests for their products have increased, particularly in Zika-affected countries like Brazil.

We tested three shirts from L.L.Bean and ExOfficio, and found that while they can help protect against mosquitoes, in our tests some worked better than others—and none were foolproof.

Plus, none of the permethrin-treated shirts were as effective against bites as an ordinary shirt that was sprayed with deet. And it’s worth noting: The shirts don’t eliminate the need for using an effective repellent on your skin. In fact, the manufacturers stress the importance of wearing the clothing along with a repellent.

Here's what you need to know about permethrin-treated clothing and how to best protect yourself from mosquito bites.

How Does Permethrin Work?

Permethrin is a synthetic version of a chemical produced naturally by the chrysanthemum flower. It’s often called a repellent, but works more like an insecticide. That is, it doesn’t stop bites primarily by preventing mosquitoes from landing on you (like deet or picaridin) but by incapacitating or killing the insects after they land and—hopefully—before they bite.

In addition, wearing the shirts for a prolonged period may create a protective buffer around you, by reducing the number of nearby mosquitoes, says Ulrich R. Bernier, Ph.D. a U.S. Department of Agriculture chemist and leading researchers on permethrin-treated clothing.

Permethrin is also used as a spray around homes and in public spaces, as a cream to treat animals, and as a lotion to treat scabies and lice on humans. The U.S. military has used permethrin-treated uniforms since the early 1990s. Deet sprayed on clothes was an option, but soldiers found reapplying it cumbersome. So the USDA figured out how to bind permethrin to fabrics. Civilian clothing based on the technology has been available since 2003.

Is Permethrin Safe?

The Environmental Protection Agency classifies it as a likely human carcinogen, if you consume it, and one study linked it to Parkinson’s disease. But the EPA says that the amount of permethrin allowed in clothing is too low to pose risks to humans, including pregnant women. Research also shows that the permethrin in factory-treated clothing doesn’t leach much onto skin, and our tests of permethrin-treated fabric suggests that to be true, too.

How Did We Test the Shirts?

We tested L.L.Bean’s permethrin-treated Crew shirt ($80, 100 percent polyester); and two similar ExOfficio shirts, the Bugsaway Breez’r ($85, 100 percent nylon) and the Talisman ($85, 60 percent cotton/40 percent polyester). All three products are treated with 0.52 percent permethrin, the industry standard. The manufacturers of all three shirts claim the permethrin will last for 70 washes. We tested them new, and after 25 washes.

As controls, we also tested untreated shirts (made of similar materials to the permethrin-treated ones) and one untreated shirt that we sprayed with Ben’s 30% DEET Tick and Wilderness Formula, the top-rated deet product in our Ratings.  

Four volunteers—two women and two men—put their shirt-sleeve-covered arms into two separate cages filled with mosquitoes. One cage had about 200 of the Aedes variety (aggressive daytime biters that can carry Zika), the other had 200 female Culex mosquitoes (a calmer, night-biting species known to transmit West Nile). The mosquitoes were all disease free.

The subjects washed their arms before testing each shirt, and the sleeves were pulled tightly against the skin. That does make it easier for mosquitoes to bite through the shirts before they are incapacitated by the permethrin, but was necessary to control for variability in the looseness of fabric on any given arm. Arms were kept in the cages for five minutes or until they received at least two bites. Lab workers counted the number of mosquitoes that landed on each arm, the number that were incapacitated or killed, and the number that actually bit.


An image of permethrin treated shirts.

The permethrin-treated L.L.Bean Crew shirt on the left did a better job of preventing mosquito bites than did the two similarly treated ExOfficio shirts on the right. None of those shirts, however, were as effective in our tests as was a shirt sprayed with the repellent deet. Note that while permethrin is often called a repellent, it works mainly by killing or incapacitating mosquitoes once they land on you, not by preventing them from landing in the first place. And even when wearing the shirts, the manufacturers say you should apply a repellent to your exposed skin, too.


Did the Shirts Work?

The permethrin-treated products did kill or incapacitate many of the mosquitoes that landed—but in some cases that didn’t happen quickly enough to prevent bites.

Notably, all four volunteers wearing Ex-Officio shirts—both new and after 25 washes—had to remove their arms from the cage before the five minutes were up, because they got at least two bites from both the Aedes and the Culex mosquitoes.

By contrast, volunteers didn’t get any bites when wearing the new L.L.Bean shirt. After 25 washes, none were bitten by the Culex mosquitoes either—though three of the four volunteers wearing the washed L.L.Bean shirt did receive bites from the Aedes mosquitoes.

The deet-sprayed shirt prevented all mosquitoes from landing, and thus, prevented all bites. The untreated control shirts did not prevent bites or landings.

Burlington, the company behind the technology used on the L.L.Bean shirt told Consumer Reports that our “data was not consistent with military, laboratory and civilian field testing” and had questions about our testing protocol.

And Haynes S. Griffin, chairman and CEO of Insect Shield, told Consumer Reports that we should have relied on a “knock down” test, which checks whether mosquitoes are incapacitated or killed when exposed to permethrin-treated clothing placed in an enclosed space.

But our experts felt that the cage test, another EPA-approved test, gave a better indication of whether the shirts actually prevented mosquitoes from biting, and also provided information on the number of mosquitoes that were knocked down, as shown in the chart below.

Aedes Mosquitoes

Culex Mosquitoes
BitesAverage KnockdownsAverage LandingsBitesAverage KnockdownsAverage Landings

L.L.Bean Crew (No-Fly Zone)

New

None716None1215

L.L.Bean Crew (No-Fly Zone)

After 25 Washings

Yes (in 3 of 4 volunteers)815None1112

ExOfficio Breez'r and Talisman (Insect Shield)

New

Yes1030Yes931

ExOfficio Breez'r and Talisman (Insect Shield)

After 25 Washings

Yes1027Yes921
Deet-Treated ShirtNone00None00
Untreated ShirtYes017Yes09
  1. Guide to the Chart: Four volunteers (two women and two men) put their shirt-sleeve covered arms into two separate cages with 200 disease-free mosquitoes, one with Aedes mosquitoes, the other with Culex. Lab staff counted the number of landings, bites, and mosquitoes that were knocked down at the bottom of the cage. The test was run until at least two bites were recorded up to a maximum of 5 minutes. Bites are whether each of four volunteers were bit. Average Knockdowns are the number of mosquitoes that were killed or incapacitated after landing on each of the volunteers. Average Landings are the number of mosquitoes that landed on the arms of each volunteer.

Is There an Extra Benefit to Killing or Knocking Down Mosquitoes

Yes, according to Bernier at the USDA. He points to a U.S. military study indicating that biting rates decreased dramatically “within the immediate area where subjects wore permethrin-treated uniforms for 9 hours.” We did not do tests to confirm that effect, but it does suggest that if you wear the clothing while sitting on, say, your deck, the shirts could over time reduce the number of bites you get by killing or immobilizing mosquitoes right around you. However, that benefit could be reduced if you change locations by, for example, walking off the deck into the backyard or are on a hike.

Can You Make Your Own Insect-Repellent Clothing?

Yes, you can buy permethrin spray designed specifically for clothing, and apply it to garments yourself. We did not test this approach, but the EPA says that clothes treated with the sprays can offer similar protection as factory-treated permethrin clothing, as long as you spray evenly and follow the package instructions. Clothing you treat yourself may need to be re-treated after repeated washings.

If you’re going to treat your own clothing with permethrin, look for sprays made specifically for clothing. The EPA advises that you don’t apply these products while the clothes are being worn, but instead spray them in a well-ventilated area protected from the wind, and hang them outdoors to dry before wearing.  

You should also be mindful of the clothes you’re working with. “Preventing bites is a combination of not only the permethrin on the surface, but also the type of fabric,” Bernier says. “And it’s not just the weight of the fabric. The weaves, and how tightly they’re woven all factor into the probability of a mosquito being able to bite you in a certain amount of time.”

All permethrin-treated clothing should be washed separately from other clothing, as some of the chemical may come off.

Can You Spray Clothes With Regular Insect Repellents?

Yes. In our tests, shirts sprayed with deet were better at preventing bites than the permethrin-treated clothing. The CDC says that any repellent that works on your skin should work for just as long when applied to clothing, though you should wash the clothing at the end of the day and will need to reapply the next time you want protection. And note that some repellents may harm fabric. In our tests, Repel Lemon Eucalyptus was less likely to damage fabric.

If You Wear Permethrin-Treated Clothing, Do You Still Need to Use a Repellent?

Yes. The CDC and the manufacturers of the products emphasize that you still need to apply an effective repellent on all exposed skin, including your hands and face. (But don’t spray repellent under treated or untreated clothes; that increases the risk or irritation and other side effects.) And if you are only wearing a permethrin-treated shirt, you also need to apply repellent to your pants, skirt and hat.

The top three insect repellents in our Ratings are Sawyer Picaridin (20 percent), Ben’s 30% Deet Tick & Insect Wilderness Formula, and Repel Lemon Eucalyptus (30 percent). All three warded off Aedes and Culex mosquitoes, as well as ticks, for at least 7 hours. And all three are considered safe by the EPA, even for pregnant women, when used appropriately.

Even when wearing repellent, you should take other steps to prevent bites, too, such as wearing socks and close-toed shoes, and avoiding tight clothes (they’re easier for mosquitoes to bite through), dark colors and perfumes (both attract mosquitoes).