My 12 year old son has a burning rash around his waistline that only flares up in the lake and pool. I thought it may be his trunks, but have tried several different types with and without elastic waist. The burning is so severe after his swim that he cries. It takes several hours for the burning to seize. I have tried applying aloe (which made it burn worse), cortisone 10, balmex, vaseline, and neosporin . He says that it does not itch . Any suggestions of what this could be?