My son developed hives on the evening of 10/7 after eating trail mix containing peanuts, almonds, cashews, raisins, and M&M's. His rash spread quickly after dinner - philly cheese steak and sweet potato fries with almond milk. We were able to clear the hives with Benadryl which we continued to give through the day yesterday. We removed all nuts and products made with nuts from his diet. The hives have returned today. Could whatever he ate or came in contact with to cause the reaction on Monday still be in his system today (Wednesday) or is he still ingesting or coming into contact with whatever is causing the reaction?