You got the best advice from the first response, Zanfel. I got PI from my dog and it got into a scratch and spread all over me. I did the steroids and calamine. I finally tried Zanfel and it was the only thing that worked.
I am seriously allergic.
A few years ago I was with a small group on a six-day canyoneering trip down Death Hollow in S. UT, which has no trail.
It turned out the entire lower 10 miles of this canyon is filled wall to wall with PI averaging about six feet deep. I envisioned myself ready to check into the hospital by the time we made it to the car.
The canyon also had a nice fast clear stream in it, which we had to wade every hundred yards or so. I just submerged myself and pack each time I waded the stream.
Never developed a single blister.
I remembered seeing your thread so I looked up a link for you this AM.