Does anyone know?

what this may be?monkey gets this crazy rash every night, sometimes in the morning. His legs turn bright red almost like sunburn, then welts come up. It doesnt seem to bother him, but I've tried everything and it won't stop coming! The doctor said it was a staph infection in his skin, but with it coming and going I don't know that I believe that. It is not rough like exzema. And no lotion or anything works to get rid of it. It is not an allergic reation, we have ruled that out also. The rash sometimes starts at his head and covers his body right down to his toes, with tiny bumps. I give up.....any help?