MY SON HAS A RASH, STARTED ON HIS LOWER LEGS

MY SON HAS A RASH, STARTED ON HIS LOWER LEGS AND BACK, TODAY IT HAS MOVED TO HIS FACE AND NECK (DISAPPEARED FROM THE FEET AND BACK), AND NOW IT IS STARTING TO APPEAR ON HIS HANDS. IT IS ITCHY AND RED. COULD THIS POISON IVY OR POISON SUMAC? HE SAYS HE DIDNT EAT ANYTHING DIFFERENT.