|Typically 2 to 3 weeks... "without treating it" they say - I would say longer without treating it..
My last contact I used Sumactin after 3 days, so it lasted a total of 6 days for a major case of PI. (sumactin.com - expensive, about $40... but I will use it again.) I then got new rashes from "contaminated" laundry - a perfect rash where my t-shirt and undwear were... that was much milder rash, but still miserable enough.. I did not use sumactin - that rash I still have, but is almost gone... (I received a new order of sumactin today, but am going to save that for the next time I get PI... which I expect will be next summer sometime...)