I'm glad you posted this! When we were down last month the back of my neck (where my bathing suit tied around my neck) started to sting - like maybe I'd forgotten to get sunscreen on and it was burned. I finally asked my husband to look at it and he found that whole area where my swimsuit tie touched my skin was all broken out. Like a bad case of teenage acne. We thought maybe some bacteria had gotten under my suit there. It was pretty painful. I made sure to use an antibacterial soap on it and got out of my wet suit right after snorkeling and it finally cleared up. Wonder if this was the same things you're describing?