When I was a teenager, I was a cutter. I've had it under control for nearly 20 years now, and have only relapsed a couple of times. It can be a frighteneing compulsion for me when I'm terribly stressed.
I have tried to quit for sooo many times in the past year. I went about 3 months without biting them but then I got really stressed and bit them off. I have tried everything and it is SUCH a dirty habit!