Now that was a nail-biter! This phrase suggests a contest or outcome that had you nervously biting your nails, so right away, nail biting doesn't have such a good image. Sticking your fingers in your mouth to gnaw on your nails doesn't exactly project confidence. Plus, it means your nails look ragged, unprofessional and in serious need of a manicure.

If you bite your nails, you're not alone. In fact, it's the most common type of "nervous habit." Nail biting is most common in children ages 10 to 18 -- about 50 percent of children bite their nails at some point. Those tween and teen years can be tough, so a little nail biting is typically just a sign of stress [source: C.S. Mott's Children's Hospital]. Some people don't break the habit until their 20s, but by age 30, hardly anyone is still a nail biter [source: WebMD].

Nail biting isn't dangerous, and it's unlikely to result in long-term damage unless you bite the nail bed, or the U-shaped area at the base of the nail where growth begins [source: Gibson]. However, excessive nail biting can cause some short-term problems, including bleeding, bacterial infections and warts around the nail bed [source: C.S. Mott's Children's Hospital]. Bacteria and viruses can also be transferred from your mouth to your nails or from your hands to your mouth if nail biting isn't curtailed. However, if you frequently wash your hands in warm, soapy water, you'll kill a lot of germs and be less likely to experience any harmful effects from nail biting [source: Gibson].

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