It could be a sign of anxiety or stress. When I was little I knew this girl who always bit her nails up to the point that they bled, and she eventually got taken to a doctor who prescribed this weird stuff she put on her fingernails. So every time she went to bite them, it tasted really bad and I think she eventually stopped. Of course if your habit is due to stress or anxiety, that’s something serious that should be looked into. I’d recommend seeing a doctor about this, even if your habit does minimal or no damage. It may be cause for something bigger that needs to get treated, and he or she can give you more resources and options. Because I’m pretty sure that if this is constant and ongoing, it is side effects of something like I mentioned. And if not, a doctor may still know what to do about it if this truly bothers you, and you want to put an end to it.