Male 12 yr old child has developed (last 24 hours) a 3 inch across, rash on the quadriceps of his left leg, The rash appears to be mapping underlying veins as it is not solid but appears to follow vein lines, its not bothering him but he says it burns a little if touched, no rashes anywhere else, weather has been quite hot last few day, if that has any bearing - wondering what to do about it please?