S.K.
I watch a little girl who used to be that way. She would get the most horrible, painful diaper rash and then on weekends when she was at home it would clear up. I was afraid her mom would think I wasn't changing her like I was supposed to. We decided to make a food diary of everything she ate and it turns out most mornings for breakfast she'd have a piece of toast with peanut butter on it. She never had peanut butter at home. When we eliminated pb from her diet the rashes (blisters) went away. Long story short, if you haven't already, start a food diary and see if there is some sort of pattern.