I've been biting my nails since I was 3, I have always done it, and especially when I start getting a bunch of twitches from my condition and it turned into a bad habit. I didn't do it out of anxiety or nervousness though, and I also have OCD which causes the habit too, I am on the verge to stopping though. I haven't been biting my nails as much, I do the skin sometimes though since I have no nails to bite during many instances. It's embarrassing.