How many washes does permethrin-treated clothing last?

Spray-on permethrin lasts about 6 washes or 6 weeks, whichever comes first, and that is what the label says. Factory-treated clothing claims up to 70 washes, but independent tests on factory-treated garments find half the permethrin gone after about 5 to 16 washes. Protection against ticks drops sharply well before wash 70. Count your washes. Retreat sprayed clothing at 6. Plan to replace or factory-retreat factory clothing after 10 to 20.

How many washes does permethrin clothing last, spray against factory?#

There are two numbers on two kinds of label, and they measure the same thing: how long the product can claim to work.

Spray-on (do-it-yourself). You treat your own clothes with a 0.5 percent permethrin spray. Sawyer's product page states "6 weeks or 6 washings (whichever comes first)" and tells you to "retreat items after 6 weeks or 6 washings to maintain protection". The label Cornell IPM quotes says the same: "Clothing should be retreated after six weeks or after the sixth laundering". UF/IFAS puts do-it-yourself spray at "about six washes". The clock runs on both washes and time, so a shirt you never wash still needs retreating at six weeks.

Factory-treated. The garment is treated before sale and sold with a pesticide hang-tag, because the EPA classes it as a pesticide product. UF/IFAS: "Many factory-treated garments claim to remain effective for up to 70 washes." It also says factory-treated items "should never be re-treated".

The 70 figure is real, and it is the maker's claim. It is not what independent laboratories measure when they wash these garments and count what is left.

Why "70 washes" and "fades in a season" are both repeated#

Search results quote the 70 because it is on the hang-tag and in the retailer copy. The field data is in journal papers, and those papers describe a much shorter useful life.

The studies are not looking at a different product. Connally's shirts and socks were bought already treated from a major factory treater, and its pants and shoes were sent to the same company for treatment. Sullivan's and Richards's workers sent their own uniforms there too.

What the studies show is slower decline in protection than in content. In Banks's machine-washed fabric, 90 percent mosquito knockdown held until about wash 10, and knockdown fell to 50 percent only at 33.4 washes. Fresh treatment has headroom, so losing a third of the permethrin does not cost a third of the protection. But it does not stretch to 70. Sullivan's team treat 70 as what the garment is "believed to" do and note that Faulde and colleagues measured more than 98 percent permethrin loss over 100 launderings.

The half-life of permethrin, in washes#

Each study reports permethrin at the start and after a set number of washes. If each wash removes a constant share of what is left, those pairs give a per-wash loss and a half-life in washes. This is our arithmetic on their figures, and it is a model: Sawyer quotes US Army studies in which 20 to 30 percent came off in the first laundering and 3 to 5 percent in each one after, so the real curve is steeper at the start.

Read it this way. The consumer garments tested lose half their permethrin in 5 to 16 washes. Only the polymer-coated military uniform, in this set, keeps around half at wash 70. Connally notes that older absorption-treated uniforms did far worse: about 50 percent gone after four washes (Schreck 1982), and more than 50 percent after two (Evans 1990).

Half the permethrin is not half the protection. Connally's 16-wash garments still beat untreated cloth. But they did not act like new ones. One hour after contact, 31 to 67 percent of ticks were moving normally after the worn and washed fabric. On pristine treated fabric the figure was 0 to 30 percent, and on untreated fabric 90 to 100 percent.

What a year of real use did to factory-treated pants#

Sullivan 2019 and Richards 2022 followed North Carolina park and forestry workers in factory-treated uniforms, which is the closest thing to a field trial of the label claim.

At three months, every one of the 17 worn garments tested still held "bioactive amounts" of permethrin, and tick knockdown was high. Two things were less reassuring. Mosquito mortality on the same worn fabric was low. And there was "approximately a 15-fold difference" between the lowest and highest swatches, which the authors put down to uneven treatment rather than use.

At one year, 8 of 12 pants had measurable permethrin, from 3.85 to 41.2 micrograms per square centimetre. The other 4 had none. Only two pairs gave a statistically significant tick kill, and both held more permethrin than the unworn control. The authors expected "zero or low permethrin content in clothing after one year of wearing and washing", and found it in five of twelve. They concluded the result "suggests the need for annual or semi-annual re-treatment or replacement".

One limit matters here: washes were "not numerically tracked", so a year of wear cannot be converted into a wash count. Batch variation matters too. Unworn pants treated in different batches over three months held between 73.57 and 117.25 micrograms per square centimetre, so two "identical" garments can start far apart.

Is factory treatment still better than spraying your own?#

Usually, yes, if you mean consistency and wash life. UF/IFAS: factory-treated clothes "appear to offer more consistent and longer-lasting protection", citing Vang 2022. Six washes for spray against 70 for factory is a fair ranking, even though both numbers are labels.

Fresh spray is not weak, though. In Vang's fabric tests, Sawyer-sprayed fabric carried the most permethrin at the surface, where insects touch it: 32.68 micrograms per gram, against 23.35 for factory-treated fabric. The ranking from mosquito repellency showed the factory fabric highest at 53 percent, but differences between treatments were "not significant". Spray's problem is how quickly it leaves, not how well it starts.

The decision, by use:

• Weekend camping, a few trips a season: either works. A sprayed outfit washed after each trip lasts about six trips or six weeks.
• Hiking or working in tick country every week: factory-treated outer layers, plus a wash log. Plan to replace them, or send them back to a factory treater as the study workers did, after 10 to 20 washes. That is the range Banks and colleagues suggested, and it fits the half-lives above. UF/IFAS says never to re-spray factory items.
• Footwear and gaiters: spray them. Connally's treated shoes, worn but never washed, "remained as toxic to the ticks as pristine treated shoes". Socks held more permethrin than shirts after 16 washes. See footwear and socks for the rest of what goes on your feet.

Which garments to treat, and what not to wash them with#

Only outer clothing should be treated. The EPA says permethrin "is not to be applied to certain clothing such as underwear". In layering system terms, that means the moving layer and shell trousers, socks and footwear. It does not mean the base layer next to skin, and it does not mean the insulated camp jacket you rarely wear in the brush.

Fabric changes the dose. Sullivan cites earlier work in which unwashed factory-treated 100 percent cotton held 29.2 micrograms per square centimetre and a 50/50 cotton and polyester blend 6.3. Most published wash data is on cotton, so the figures above are least certain for nylon and polyester trail clothing.

A care routine that slows the loss#

These steps come from the label, UF/IFAS and the test results. Each one is backed by at least one of them.

1. Wash treated clothing separately. The EPA says the label requires it, because "small amounts of permethrin can come off in the wash".
2. Machine wash, gentle cycle, mild detergent, no bleach, no fabric softener (UF/IFAS). This is the same mild, additive-free wash that washing down gear calls for, though permethrin clothing should not share the load. In Banks's test, machine washing kept permethrin longer than simulated hand washing: 50 percent knockdown lasted 33.4 machine washes against 17.6 hand washes.
3. Line dry. UF/IFAS says to line dry "whenever possible instead of using a clothes dryer". Connally's garments, which lost 50 to 90 percent, were tumble dried at about 57 degrees C.
4. Do not iron. Ironing cut permethrin by 96.7 percent across a simulated three months in Banks's test.
5. Wash less. Every wash costs a share. Airing a trail shirt between short trips is cheaper than a wash cycle.
6. Store it dark. Sawyer recommends black plastic bags between uses. Pack it away dry, as in gear storage.

Check this before you buy, and keep a wash log#

The hang-tag of a factory-treated garment is a pesticide label, so read it like one:

1. Find the registration. Factory-treated clothing sold in the US must carry a pesticide use label. If there is no hang-tag, there is no label to check.
2. Read the wash claim and the species list. Note the number of washes and which pests it names. Protection applies only to skin the fabric covers.
3. Check the fabric. Cotton has the most published wash data. Light synthetics carry less permethrin per area.
4. Start a log on day one. Make a mark on the inside care label with a laundry marker each time it is washed, and write the treatment date for sprayed items.
5. Set your own retreat point. For spray: 6 marks or 6 weeks, or earlier if your product's label says so. For factory items in heavy tick country: plan replacement or factory retreatment at 10 to 20 marks, or yearly, whichever comes first.

Common mistakes#

Trusting "70 washes" as a tick-season guarantee. It is a claim about a lifetime. The independent data puts half the permethrin gone by 5 to 16 washes on the garments tested.

Forgetting the six-week clock on spray. The label runs on whichever comes first. A jacket sprayed in April and never washed is out of date by mid-May.

Tumble drying on high and ironing. Both remove permethrin faster than the washing does.

Heat-setting a water repellent on treated trousers. The 20 minutes of tumble drying or the ironing that reproofing rain gear uses to cure a DWR is the same heat that strips permethrin in the tests above. On one garment, decide which finish matters more.

Re-spraying factory items. UF/IFAS says not to. Replace them or have them factory retreated.

Treating the base layer. Only outer clothing is meant to be treated.

Assuming permethrin replaces skin repellent. Treated cloth protects only the skin it covers. Use a repellent registered for skin on everything else.

Frequently asked questions#

How many washes does permethrin spray last on clothes?#

Six washes or six weeks, whichever comes first. That is the wording on common spray labels, and UF/IFAS gives the same figure of about six washes for do-it-yourself treatment. Some shelf products are labelled for less, and Cornell IPM has found sprays that last only two weeks. Read the label of the product you actually bought and count both washes and days.

Does factory-treated permethrin clothing really last 70 washes?#

Seventy washes is the claim made for many factory-treated garments, not an independent field result. In laboratory wash tests on factory-treated clothing, shirts lost about 90 percent of their permethrin in 16 wash and dry cycles, and machine-washed fabric lost 81.6 percent in 30 washes. Protection fades more slowly than content, but no study we found showed full protection at 70.

Does washing remove permethrin from clothing?#

Yes. The EPA says small amounts come off in the wash, which is why labels require treated clothing to be washed separately. UF/IFAS says a small amount is washed off "each time". In measured tests, simulated hand washing removed more than machine washing, and tumble drying and ironing added to the loss. Wash gently, line dry and wash only when needed.

Can you re-treat factory-treated clothing with permethrin spray?#

UF/IFAS says factory-treated items should never be re-treated. The authors of a one-year study of factory-treated work uniforms concluded that annual or semi-annual re-treatment or replacement is needed to keep them protective. The two agree on a practical answer: do not spray over a factory treatment at home. Replace the garment, or return it for factory retreatment.

How long does permethrin last on clothes that are never washed?#

On spray labels, six weeks. The time limit applies even without washing. For factory-treated items, the clearest unwashed result is footwear: treated shoes worn for 16 days without washing stayed as toxic to ticks as new ones. Sawyer recommends storing treated items in black plastic bags between uses to protect them from air and sunlight.

Does permethrin clothing work against mosquitoes as well as ticks?#

It works against both, but the effect on mosquitoes fades sooner. In factory-treated uniforms worn for three months, tick knockdown stayed high while mosquito mortality on the same fabric was low. In laboratory tests, factory-treated fabric still sharply reduced mosquito biting. If mosquitoes are your main concern, treat the 6-wash and replace-early rules as firm limits.

Is permethrin-treated clothing safe to wear every day?#

The EPA's 2009 assessment, which included military personnel wearing treated uniforms daily, found factory-treated clothing "unlikely to pose any significant immediate or long-term hazard". In the three-month worker study, absorbed doses averaged under 4 micrograms per kilogram per day. The authors called that more than an order of magnitude below regulatory health goals. Permethrin spray is toxic to cats until it has completely dried.