Hello, my son, who is now 3, has a birthmark on his back that his first pediatrician consistently asked if it ever became inflammed. He was under 1 when we moved, and at that point, it never had. Since then, on several occasions, usually when it has been very hot (we moved to a desert) it has become inflammed and white in the middle, a lot like a bug bite or pimple. None of his other doctors have showed any concern of this, but his first always wanted to know if it ever had done this. What could be the cause?