Dear friend —
Dermatophagia is not intrinsically sinful. It's probably an expression of Obsessive-Compulsive Disorder (OCD), which is related to scrupulosity: the idea that things that aren't gravely sinful, are.
Suppose we grant that dermatophagia is cannibalism. People eat placentas, which is more cannibalistic than what you are doing and there is nothing wrong with that. Besides, scabs and skin cells are dead.
As long as you are not permanently mutilating yourself, there would be no grave sin involved. Even then, it sounds like you are not doing this with total freedom of the will, and you can't commit a mortal sin (that is a sin that would send you to Hell) if you don't freely commit it. Perhaps there might be a venial sin (a sin that doesn't send you to Hell) if you are damaging your body.
That being said, you should seek professional medical help because what you're doing is not normal and could be self-destructive, especially if it keeps wounds open. It could cause scars as well.
As for masturbation, you are still considered a virgin if you've only committed masturbation.