I think it was the field work. Im a grad student who works in the forest and I did about 46 hours of field work in 2 weeks. It was 108 degrees out and about 80-90% humidity and, since we're working with chain saws and such, we have to wear long pants all the time.

I used hydrocortisone and it cleared up within hours and, since field season has pretty much stopped, it hasn't happened again. I wish there was a way to NOT sweat profusely. But I guess it's to be expected when you're working 12 hour days in that kind of heat. Plus our work is pretty much cutting and carrying logs through the forest so I was sweating buckets!