Bite Your Nails
This can damage your teeth as well as the skin around your nail bed, which can lead to infection. You also may get more colds and other illnesses when you put your fingers, which often carry germs, into your mouth. It can help to keep your nails neatly trimmed or manicured. If stress could be the reason for your habit, you might try things like exercise to manage it. Talk to your doctor if you want help stopping.