It's/permethrin a synthetic analog of pyrethrin, extracted from chrysanthemum flowers. Pyethrin is used as an insecticide on plants and has a very short residual effectiveness (ca. < 1 day).
The synthetic compound permethrins an ester, and on contact with the skin it is quickly broken down by esterase enzymes. That's one of the reasons it can't be used as a topical repellent and also why it has low toxicity to humans.
I keep 3 sets of clothes (shirt, pants, socks) and a set of coveralls treated with permethrin. I've been treated for lyme several times, but ZERO ticks or tick bites when I've had the treated clothes on. The stuff works great.