I recently started developing the same thing. Since the first time it showed up was with a new pair of shorts, I thought I might be developing an allergy to the silicone in the gripperbands or something like that. Took a baby benedryl, rinsed it off with cool water and put aloe vera on it and it was cleared up by the next day. Since I got it again with an old familiar pair of shorts yesterday, I guess it is heat rash and will start putting on an allergy cream before I put on the shorts- good to know what it is.