Make sure that you wear loose cotton clothing as much as possible. Cotton wicks away moisture and keeping the fabric loose will reduce the amount of friction on your skin. Even if you are not normally prone to acne, your body may be exhibiting "acne mechanica," a term used to describe blemishes that result from pressure, friction, and heat. The strap on your sports bra may be irritating your skin or spending an hour playing beach volleyball in a spandex bathing suit may be to blame. It's a common sports-related condition that can be combated with typical acne treatments and you won't have to give up on working out.