Poison Ivy is a plant that can cause what we call a type 4 hypersensitivity reaction in the skin. This is basically a fancy way of saying that skin often has an allergic reaction to the oils in poison ivy. This allergic reaction can cause redness, blisters, and really bad itching. The allergic reaction itself is typically not dangerous as long as the poison ivy is not eaten and as long as it is not burned. This is because the reaction on the insides of the GI track and lungs can be very uncomfortable, though rarely dangerous. Probably the biggest complication that comes from poison ivy is the skin infections that people get after they scratch the area. Scratching an area of skin over and over again can introduce bacteria under the skin and cause an infection.
I suggest that you schedule an appointment for your son with his primary care physician
). He or she can look at the area of irritation around his mouth and see if it looks like a type 4 hypersensitivity reaction. If it does, then your son may get a small dose of prednisone to take to calm down the inflammation. Do not put any over the counter creams on his face without his doctor's permission. Good luck.