Children bite their nails for many reasons -- out of curiosity or boredom, to relieve stress, to pass the time, or from force of habit. Nail biting is the most common of the so-called "nervous habits," which include thumb sucking, nose picking, hair twisting or tugging, and tooth grinding. (None of these necessarily signal anxiety, so "nervous habits" is something of a misnomer.)
Nail biting is most common in high-strung children, tends to run in families, and is the most likely of the nervous habits to continue into adulthood. About one-third of primary school students and one-half of adolescents bite their nails, at least for a time; between one-quarter and one-third of college students say they still bite their nails.
If you know or suspect that a particular situation is making your child anxious -- a recent move, a break-up in the family, a new school -- make a special effort to help them talk about their feelings.
If your child's nail biting seems self-destructive, however, it's time to call their doctor or school counsellor. You should be concerned, for example, if their fingertips are ragged and bloody, or if in addition to biting his nails, they pick their skin, tugs on their eyelashes, or is not sleeping well. Also consult your child's doctor if the habit of nail biting surfaced suddenly and escalated quickly. You always want to check out the reasons behind a drastic change in your child's behaviour.
If, on the other hand, the habit doesn't seem to pose any physical or psychological threat, ignoring it is the best way to ensure that down the road your child will either stop on their own or asks you to help them quit.
If the habit bothers you, set limits. "No nail biting at the dinner table" is as reasonable a rule as "No feeding the dog from your plate." At other times, explain in a compassionate way that you know they can't help it, but you don't like to watch them biting their nails, so you're going to another room for a few minutes.
The most important thing is to keep what's basically a nuisance from escalating or getting laden with emotion. Stifling your anger for as long as you can and then snapping, "Stop biting your nails! I can't stand it!" is a recipe for disaster. If the situation is already tense, defuse it by being straightforward -- "I think we're both getting too worked up over this. I'm going to take a break from it for a while."
As long as they're not hurting themselves and don't seem stressed out, your best bet is to wait out the habit. The less fuss they associate with their nail biting, the more likely they'll stop on their own when they're ready -- and the more likely they'll feel comfortable asking you for help.
If your child feels that reminders from you will help, choose a subtle signal -- a light touch on the arm or a code word. Encourage them to become more aware of when and where they bite, and identify some relaxation techniques they can learn -- deep breathing, or clenching and releasing their fists. You might attach a small pair of fingernail clippers to their key chain or belt loop, so they won't be tempted by snags. If they're old enough, teach them how to use an emery board and keep one on their bedside table or in a bathroom drawer.
Step three (and steps four and five and onward) are to try -- and try again. Explain to your child that different people respond to different techniques, and encourage them to be willing to try a variety of solutions if the first one doesn't work. In general, the older they are, the more responsibility they can take in this endeavour.
Children of all ages, like adults, may find a substitute habit useful (plasticine for car rides, a smooth stone to hold while reading or watching television). Let your child choose an activity. If they're under the age of 8 or 9, they might need help in making the switch: practice the alternative habit with them for a few minutes before school or at bedtime.
Calendars work well for children up to about age 9. Let your child select and place stickers on the days they don't bite their nails. For an older child, set up an incentive savings plan, in which they deposit €1 to start and then you put in €1 for every day they leaves their fingertips alone. Physical reminders work for some kids: your child may want to try keeping Band-Aids or stickers on their fingertips or painting their nails with a bite-averting solution such as Stop'n Grow. (Check any product's ingredients before trying it. Finally, remind them -- and yourself -- that habits are hard to break and that the two of you are on the same side. Take a break from habit-breaking if you need to. Eventually your patience and persistence will pay off.
There is a strong tradition here in Ireland that nail biting is associated with intestinal worm infestation, particularly if the child has a tendency to like sweet and sugary things, as indeed virtually all children do. Research has shown that there is no evidence that nail biting has anything to do with worms.