We noticed our teen son had a small, circular, rough spot on the bottom of his foot a while ago. At first we d thought he d stepped on something and it would go away. It hasn t, and is now, nearly, a dime sized black, circular rough spot. He thinks he caught it on something and the black is caused from dried blood as if it were a very dark blood blister. But the skin is hardened in that spot. Any ideas? Does he need to see our doctor?