This kind of sounds more like a habit/OCD, I do not know what to say, perhaps talking to a therapist, maybe he or she can help you find something healthy to replace this habit or teach you how to distract from the urge to do this.
I once went through something similar but it was more of trying to scrape any zits that use to form on my scalp during the hot weather after I had been out doing yard work, perspiration use to really triger the zits, I honestly do not know how I stopped this, I think it was when my mother-in-law brought this to my attention, by asking me if I had "cooties", she made me aware that I was fiddling with my scalp and gave her the impression I had something itching me, it wasn't the itchies I explained, I just didn't like having the zits on my scalp and felt the need to scrape them off. . . I know there are many things that may be weird that compell us to doing this stuff, I still would talk to a therapist if you find you can't stop cause it can lead to infection if the tear in the scalp from picking the scabs gets deep, it can happen doesn't mean it definately will but who wants to risk it, right?
I wish you luck in your effort to stop this compulsion, give therapy a try, if it doesn't subside.
Take care,

DE

In giving advice seek to help, not please your friend
SOLON