Seems like I have to post this every year as people dont do serious research when they want to solve a problem.
First off, permerthin has a long history of safe use and is in fact prescribed as a treatment for scabbies in INFANTS at 10x(5%) the clothing treatment concentration. Thats applied directly to the skin as a lotion, so if you are worried about ticks in your nether regions and are not treating underwear you are being overly cautious. I find treated exterior clothing to be so effective treating underwear is not necessary but if you experience dense tick populations I'd consider the risk/benefit as worth it. If you are not sure about your upcoming exposure- carry a 3-4oz spray bottle to treat underwear on the trail, it will also be a great conversation starter at shelters
while you dry them.
Yes it is toxic in heavy concentrations and you are most likely to get an excessive "dose" by inhaling aerosol spray and while mixing concentrate. So if spraying clothing, do so with proper ventilation.
https://phpa.health.maryland.gov/IDE...permethrin.pdf
Second, you can find videos online of ticks being exposed to proper concentrations of permetherin and they act like they have been exposed to a nerve agent. I see this behavior on the trail, pretty much immediately upon contact with treated clothing they loose motor control and soon fall off.
If you dont see this happen, I'd wager your treatment is somehow failing. My main theory for how this can happen is poor penetration/saturation caused by l water repellency of many fibers used in trail clothing. I see that with mine- it wants to bead up rather than penetrate. So you have to do what ever it takes to get a good coating so it wets out the fabric. Spraying usually takes multiple passes with time between to see the entire garment wet. This tendency is also likely aggravated by those who fear permetherin thinking to avoid "exposure" with minimal applications, dont drink it or smoke it and you'll be fine. And of course despite the claims for withstanding multiple washings, its certainly not going to help your protection by washing some or all of it off, so consider at least touching up your application after washing.
Here is some info on what the military did to establish the safety and efficacy of permetherin.
https://www.ncbi.nlm.nih.gov/books/NBK231561/
Tips- Permertherin has a good shelf life(3-5 years as a concentrate) so if you hike much, buy concentrate and mix it your self(wear gloves) a quart of 36% cost about the same as a quart of Sawyer .5%. Concentrate is often available at local farm supply stores.
Once applied and dried you are dealing with a particulate on the fabric- which means if you are going to wear the same clothes for a month its going to wear off and be affected by sweat too. I have no advice on that situation as I only go 3-4 days on a set of clothes regardless of how long I'm out which means at a minimum I wash/rinse them. With the Sawyer claim of 6 machine washings, I figure 3 rinses is about all one should expect to not impact effectiveness on the trail.