Is it normal that i bite and pick the skin off my fingers?

For the past 4 or 5 years I have this really obsessive habit of chewing or picking the skin off my thumbs and sometimes pointer finger. Sometimes I bite them so much that they start gushing blood and now they have scars and sometimes infection, but I still can't stop!It used to just be a nervous habit, but now I do it all the time. Does anyone else do this?Do anyone know how to stop?