Is it normal to constantly bite off loose skin inside of your mouth?

I feel like a lot of people do this, but I do it to the extreme that it becomes obsessive until the skin's gone and i don't care how stupid I look when I'm doing it. It's kind of a recent thing for me, though--I've only been doing it for about two years. My parents say it's stress, but honestly, it would have to be a really delayed reaction because I'm never currently stressed when I do it. Also, I'll sometimes go a whole month w/o doing it...and then start back randomly. It's not just the inside of my cheeks, though--it's also the inside and outside of my lips (especially the corners). Basically, any loose skin in/around my mouth.