RF,
I have wondered that for years and still don't have an answer, the Army uses it religiously, that's how I learned about it. When I was in Korea last year it was a requirement to turn in two uniforms to be treated.
I mix up the strongest solution on the instructions, completely soak my clothes, air dry them, then wash one time in scent free laundry detergent. I can't smell anything and when wearing my treated clothes I have yet to get ticks. I also blouse my boots and tuck in my undershirt. Chris