I know of a 4 year old who will present with a red rash on the left side of his chest (only location of rash) while he's in the shower. He isn't using any new soaps/shampoos, the laundry detergent hasn't been changed, the water isn't terribly hot, and it only shows up in that one area of his body and only while he's in the shower. It may last for a few hours and becomes itchy.