Quoting Abi Lynn:" Could be a heat or friction rash. Just don't scrub them in the shower, wash them lightly. Also when you're ... [snip!] ... the areas that it's happening. I picked this up working in a factory with no air conditioning. The baby powder does wonders!"
Quoting ~AsherLee~:" Just use it like lotion, it prevents the sweat and rashes. I use it to prevent chub rub when I wear skirts."