Permethrin is a manmade chemical compound that behaves similarly to the natural extracts from the chrysanthemum flower. However, permethrin is not as biodegradable and is more lethal to pests in lower concentrations than the natural extracts it mimics.
The substance is commonly found in lice treatment shampoos (in a 1% concentration), and in creams used to treat scabies (in a 5% concentration), and has been used for years without any known health risks.
The Environmental Protection Agency (EPA) has deemed permethrin safe for external usage, regardless of age, because it is not readily absorbed into the skin – even in liquid form. When applied to the skin, permethrin could cause some tingling and irritation. Fortunately, though, less than 1% of the substance is absorbed into the body in this manner.
Nevertheless, use of permethrin on the skin is not recommended, mainly because it is not very effective as a skin repellent – especially compared to substances like DEET and picaridin.
However, while permethrin is safe for dogs, according to the National Pesticide Information Center (NPIC), wet permethrin is extremely toxic to cats, aquatic life (in both salt and fresh water), and is “highly toxic for bees and other beneficial insects” in any form.
Dry permethrin on treated clothing should not cause any problems for humans and most wildlife, though. According to the University of Rhode Island’s Tick Encounter Resource Center (TERC), a person who weighs 140 lbs. would experience no negative effects if he or she were exposed to 32 grams of permethrin per day. Given that an entire bottle of clothing treatment spray contains less than 1 gram of the substance, using permethrin to treat clothing appears to be safe.
Additionally, the EPA has deemed permethrin safe for pregnant women, as well as infants and toddlers – even if they get the clothing in their mouths. In fact, the risk of illness or bad reactions for toddlers who are exposed to permethrin-treated clothing is 27 times below the EPA’s Level of Concern (LOC).
These facts about dry permethrin are important because, when treating clothing, the substance must be applied to both the inside and outside of the clothing. This strategy protects against ticks or other biting insects that might crawl under clothing.
Another important fact from the EPA to keep in mind is that permethrin-treated clothing should be washed separately from other, non-treated clothing (e.g. underwear). Studies have shown that the substance will come off over the course of several washings, and can be transferred from to clothing that has not been treated.