What Is The Treatment For Rashes Around The Mouth?

My 8 year old son has a rash around his mouth that I have never seen on anyone before. It happened within a matter of a few hours. At first I thought he had purple food-coloring stains on the skin around his mouth, but on closer inspection I see that they are tiny bruises under the skin- formed like a rash. it goes all the way around his lips and has gotten darker. Should I try hydrocortisone, benadryl, leave it or take him to the doctor's?