Biting your nails may not seem particularly damaging at first. However, nail-biting can affect your teeth, do damage to your nail beds, and put you at risk for getting sick from all of the germs. You should kick the habit as soon as possible as it usually is caused by an underlying mental health issue that may need to be treated. Studies show that biting your nails can be a reaction to stress, frustration, or anxiety. The data shows that 60% of children, 45% of teens, and 30% of adults bite their nails.