Some people twirl their hair. Some fiddle with a ring. Others bite their nails.

When we are nervous or anxious, it's not uncommon to engage in repetitive behaviors. Unfortunately, nail biting in particular isn't innocuous. There's even a medical term for it: onychophagia.

"Nail biting generally begins in childhood and adolescence," says Dr. Maria Scremin, a primary care provider at Cedars-Sinai. 

If you're a nail-biting adult, chances are good that you picked up the habit when you were young. But there are good reasons to break the habit. 

While there are no clear-cut reasons for nail biting, a variety of factors can increase the likelihood of you chewing on your fingernails. 

• Genetics: Kids whose parents bite their nails are more likely to follow suit—even if the parent stops the behavior before the child is born.
• Anxiety: Nail biting can be a sign of anxiety or stress. The repetitive behavior seems to help some people cope with challenging emotions.
• Boredom: Behaviors such as nail biting and hair twirling are more common when you're bored, hungry, or need to keep your hands busy. 

For most people, nail biting is automatic: You do it without thinking about it.

While it can occur without any underlying psychiatric conditions, it's also associated with attention deficit hyperactivity disorder (ADHD), separation anxiety, tic disorder, and other mental health problems. 

In rare cases, nail biting may be a side effect of medication.

"If your habit is a new one and coincides with a new prescription, talk to your doctor about whether nail biting is a possible side effect," Dr. Scremin suggests.

Nail biting is rarely dangerous, but it can compromise your overall health, especially if you chew below the nailbed. 

Any biting and picking below the cuticle can create structural changes in the base of the nail that alters the way the nail grows out.

But the biggest concern for nail biters is infection. 

"Over time, bacteria can build up in the skin around the nail causing redness, irritation, and swelling," says Dr. Jasmine O. Obioha, a dermatologist at Cedars-Sinai.

Topical treatments like cortisone can reduce inflammation and offer relief, but sometimes doctors have to drain the area to relieve pressure. 

Nail biters are also more prone to develop colds and flu. After all, your hands are teeming with bacteria, especially beneath the nails.

If your fingers are always in your mouth, the bacteria they touch land there too. 

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It can be tough to stop biting your nails, particularly if you've been chewing them since childhood. These strategies can help:

When you go to bite a nail, consider how you're feeling or what you're doing.

Are you hungry? Stressed? Bored?

Once you know what triggers the nail biting, you'll be better equipped to curb it.

If your teeth can't grab onto a nail, biting them will be less satisfying. 

Covering your nails with a barrier like gloves, mittens, socks—or using retainer-style or bite-plate devices in your mouth—can act as a deterrent for nail-biting behaviors.

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Special nail polishes are available that have a bitter taste to them.

If your nails are coated with a nasty taste, you may condition yourself not to bite them.

Keep your hands busy with a stress ball, worry stone, or even a clickable pen.

You might also consider chewing gum to keep your mouth occupied. 

Instead of trying to stop biting all of your nails overnight, take a gradual approach, focusing on one nail at a time.

Once you succeed with one nail, add another until you're able to stop biting the nails on your whole hand. 

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Be gentle with yourself.

Kicking a childhood habit is complicated—and sometimes the inability to quit is a sign of a more serious psychological or emotional issue.

If you've repeatedly tried to quit without success, talk to your doctor.

There are focused treatments—both medical and psychological—that can help, such as cognitive behavioral therapy and decoupling strategies.

In the meantime, watch out for redness, pain, swelling, peeling, or changes in the nail. Pitting, discoloration, and abnormal growth may be a sign of a medical problem. If something unusual is going on, check with a doctor.

"It's always best to get nail issues evaluated," Dr. Obioha says.