My best guess is that it is an angioma, a benign collection of blood vessels. These occasionally bleed if rubbed, but not much or often. They don't go away on their own, and are easy to cauterize if they are bothersome, though it is OK to leave them alone.
Having said all this, I really can't tell you for sure what it is without examining you, so if you want to know, you'll need to see a doctor.
Take care.
Dr. Rockoff