If I know I'm going to sweat like with exercising ....I wear a breathable sports bra and you might laugh but I put a couple folded paper towels to catch the sweat. Obviously you can't do this if you're out, because it might move and show ...then people will think you're stuffing the bra lol. I was going to say if you're large breasted ......its possible to have a fungus problem but it sounds like this is sweat build up. Avoid the heavy padding if you're going to be sweating and soak your bras / wash frequently. I never put them in the washing machine or dryer because this ruins them. I squeeze them gently after hand washing and then pat in a towel then put on a hanger. Sweat build up on padded undergarments can take on a life of their own lol - ask mothers who have sons in hockey or football. Let your bras soak a little, then wash by squeezing gently.