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I purchased a spray-bottle of Sawyer 0.5% permethrin to treat some of my clothing in preparation for a backpacking trip. The spray nozzle turns out to have been quite a bit more generous than I anticipated - a fact that I realized only after using roughly twice the recommended amount on my first outfit. In all other respects I have followed the directions on the packaging to the letter.

Is the overtreated outfit unsafe to wear? Would it be an overreaction to wash it once the treatment dries?

EDIT Just returned from our trip. Wore the aforementioned outfit without washing for a couple days on the trails. 100% anecdotal, but no tick bites, few mosquito bites, and most importantly none of the adverse symptoms associated with permethrin.

Great weather, too!

Conduit
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2 Answers2

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I am almost certain that you will be safe.

Permethrin is not particularly toxic to humans, and exposures of notably higher concentrations than what you used for the clothing treatment have been found to not be a significant issue. In fact, there are treatments for head lice using 1% Permethrin, applied directly to the scalp, so I wouldn't worry too much about using a bit too much on the clothes, particularly since when it dries, the exposure risk lowers.

According to the fact sheet, permethrin is "efficiently metabolized" by the liver and has a very high lethal dose (though that doesn't mean you should drink the stuff). High enough that there is a very generous safety margin in products for use to treat clothing, where the quantity suggested to use is considered safe for pregnant women (and is even recommended by the CDC for such use). I don't think you could have applied enough to be an issue.

If you are truly worried, you can wash the clothes to remove some of the permethrin. The more vigorous the wash cycle, the more will be removed, as agitation is the primary mechanism of removal for the permethrin.

fyrepenguin
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drugs.com notes the Usual Adult Dose for Scabies is a Permethrin topical 5% cream, applied by thorough massage into the skin. 30 grams. That's essentially 1,5 grams pure permethrin applied to the skin directly.

I don't recommend doing so unless it's required, but if your spray is 0,5% and you've applied twice what is recommended, it would seem you're still way within safety margins. You're not massaging it into your skin so the effect per dosage on you will be much lower than the cream would have.

Worst case effects if you'd do this every so often (or are overly sensitive to it) would be pruritus, an itch. Washing it out would in my opinion be an overreaction indeed.

Mast
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