My nephew is visiting and after the 5 hour drive to get here, during which he was in a seldom-used 7th generation diaper, he's got a rash over his midsection - about nipples to knees. Three weeks ago after also wearing a 7th Generation diaper for a long drive he had a milder version of the same thing. It was just clearing up when this one appeared. It's red, slightly raised bumps, not itchy, no fever, no oozing, no diarrhea, and his appetite is the same. What could this be? Just some skin sensitivity to something in the diaper? Or something else?