blotchy skin

My 15 year old son develops very red but not itchy blotches whenever he bathes, swims or showers.
He had infantile excema and occasionally has excema on his arms still.  He finds it embarrassing, especially during holidays when he would like to spend a lot of time in the swimming pool. We haven't been to our GP yet as it's really not a serious problem.  Could anything help which would be tolerated by a 15 year old?

Thanks