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Breaking the Nail-Biting Habit

People who would like to drop their nail-biting habit may want to consider taking N-acetyl cysteine (NAC). Is there any scientific support?

Ask people who bite their nails why they do it and you are likely to get a range of answers: stress, boredom, anxiety, excitement. Sometimes a hangnail or roughness can trigger the urge to bite. It is estimated that almost one-third of the population has had a nail-biting habit at some point.

Trivial Questions:

Doctors love big words that are hard to pronounce. That’s the case for describing patients who have a nail-biting habit. This medical condition is called onychophagia. It comes from the Greek onycho which means claw or nail plus the word phagia which translates as to eat.

Another similar term doctors love is trichotillomania. It refers to hair pulling and comes from the Greek word thrix or trich translated as hair, tillo or tillein to pull and mania or madness. It is less common than nail biting, but still problematic, especially for young women.

Is It Possible to Break a Nail-Biting Habit?

Family and friends often consider both nail biting and hair pulling annoying behaviors, especially in children. For someone who has never suffered these problems, it can be hard to understand why it is so challenging for individuals to overcome these habits. Both hair pulling and nail biting are considered a type of obsessive-compulsive disorder.

It may not be as tough as breaking an addiction like smoking, for example, but it can be far from easy. How do people stop biting their nails?

Some doctors prescribe medications such as the antidepressants fluoxetine (Prozac) or clomipramine (Anafranil). Others recommend “aversion therapy.” That might include nasty-tasting nail polish. Gloves or bandages are other “treatments.” Habit reversal training (HRT) is another approach.

Readers of our syndicated newspaper column have asked us for affordable and benign suggestions.

Help for a Nail-Biting Habit:

Q. I’ve been a nail biter since I was a kid. The only way I had nice nails was to spend a fortune at a salon.

When I learned that NAC (N-acetylcysteine) is known to help with BFRBs, body focused repetitive behaviors, such as nail biting, hair pulling or skin picking, I decided to try it. After a few months of taking this supplement, I had beautiful natural fingernails for the first time in my entire life. A most welcome extra benefit of NAC for me is I have absolutely no desire for alcohol and my appetite and craving for unhealthy foods are just gone.

My primary care doc is fairly progressive, but he knew nothing about NAC other than its use in the ER to reverse acetaminophen overdose. He gave me the stamp of approval after seeing the changes in me. I take several supplements, but this one has had the most profound and positive change to my overall health.

A. Thank you so much for a fascinating testimonial. As your doctor told you, NAC is “the mainstay of therapy for acetaminophen toxicity” (StatPearls, Feb. 19, 2023).  The FDA approved it for this indication in 1985.

There is far less research on its use to control body-focused repetitive behaviors with a compulsive component, such as nail biting or hair pulling. A review of the research noted that only a few clinical trials of NAC for this purpose have been conducted (International Journal of Environmental Research and Public Health, June 2022).

We haven’t seen any studies showing that NAC can reduce the urge for alcohol or junk food. However, a small study in Indonesia demonstrated that it helped men stop smoking (Cureus, Feb. 16, 2024).

NAC has a good safety profile. It may cause nausea, vomiting or diarrhea, and occasionally people develop reactions such as rash or flushing. Headache, hives or fever may occur at the high doses used to treat acetaminophen toxicity (American Family Physician, Aug. 1, 2009).

Here’s a message we received during the pandemic:

Q. I have been feeling very anxious about being stuck at home because of the coronavirus. All the stress has led me to start biting my nails again. My thumbs look awful and my wife gives me a lot of grief about them.

I have sometimes used instant glue to stop myself from chewing on the rough spots. I figure that it’s not healthy to swallow the dried glue. Do you have any other ideas about how to overcome my horrible nail-biting habit?

A. Biting your nails is a particularly bad habit when you are trying to avoid infection with COVID-19. No amount of preaching about keeping your hands away from your face (and your fingers out of your eyes, nose and mouth) will give you the willpower to just stop cold turkey.

NAC to the Rescue:

Australian scientists may have come up with a promising aid almost by accident. According to The Wall Street Journal (Dec. 28, 2020), they were testing a nutraceutical, N-acetyl cysteine (NAC), for its ability to help people with bipolar disorder. Unexpectedly, a few of the people in the study stopped biting their nails while they were taking the supplement (CNS Spectrums, Nov. 7, 2014).

A randomized controlled trial found that NAC was more effective than placebo in helping youngsters stop biting their nails (Anti-inflammatory & Anti-allergy Agents in Medicinal Chemistry, 2013). The study was small, however. A review in the International Journal of Environmental Research and Public Health (June 2022) offers additional scientific support for NAC against a nail-biting habit.

NAC is sold without prescription as a dietary supplement. It is inexpensive and and considered safe. Physicians also use this antioxidant to treat the damage done to the liver by an overdose of acetaminophen (Tylenol). It may be helpful against other obsessive grooming behaviors such as hair pulling (Clinical Neuropharmacology, Jul/Aug 2019).

Readers Share Stories About Treating a Hair-Pulling Habit:

One reader offered this anecdote:

“I have been a nail biter for 40 years and am currently a mental health counselor with a master’s degree. A compound called NAC works well for trichotillomania, which is a disorder of pulling out eyebrows, eyelashes, and/or hair on the head compulsively. Nail biting falls in the same general category, called a body-focused repetitive behavior.

“After reading a study showing that NAC significantly helped trich, I thought I would try it for my nails. I take it in the morning, but I notice it starts to wear off between 1:30 and 3:30 pm. So I take another dose.

“The downfall is that once the stuff is out of your system, it’s easy to unconsciously bite them all off again. I have been practicing this for almost a year now and have become much more self-aware so that I don’t ruin weeks of progress by missing a dose.

“You have to be patient and expect there to be slip-ups and mistakes. Now I keep a bottle at home and one at each of my two jobs, so I always have it available. If it is 3 or 4 o’clock and I feel my fingers slipping into my mouth, I take another dose!

“I have had no side effects and from the research I have read, that’s pretty typical. I buy it over the counter, although it can sometimes be expensive.”

Another reader offers a similar story, although the motivation for taking NAC was different. After going through cancer treatment, she began taking this compound to support her liver.

She found she no longer craved alcohol or unhealthy foods:

“After a few months of taking NAC, I also noticed I had beautiful natural fingernails for the first time in my entire life. I’d been a nail biter since I was a kid and the only way I had nice nails was to spend a fortune at a salon. I’ve since learned that NAC is known to help with body-focused repetitive behaviors such as nail biting, hair pulling, skin picking, etc.

“My primary care doc knew nothing about NAC other than ER use to reverse acetaminophen overdose. He gave me the stamp of approval after seeing my changes.”

We would welcome more research and feedback from readers about this dietary supplement.

Other Approaches to Overcoming Nail Biting:

NAC is not the only solution nail biters have tried. We heard from another reader years ago desperate for help.

Q. I have bitten my fingernails for years. I’ve stopped several times for as long as six months, but just like a smoker, I can’t kick the habit for good.

The biggest problem is when I’m reading, watching TV or driving. It leaves my fingers and cuticles ugly and very sensitive. How can I quit?

A. There are surprisingly few well-controlled studies of treatments for nail biting. Many health professionals view this habit as a manifestation of obsessive-compulsive disorder. Some data suggest that cognitive behavioral therapy could be effective (Dermatologic Therapy, Nov. 2020). Therapy aimed specifically at habit reversal has shown the most promise. If the nail biter has other signs of OCD, the therapist may also prescribe an SSRI such as fluoxetine.

Over-the-counter approaches involve painting bitter-tasting substances on the nails to remind the person to stop biting. They include products such as Mavala Stop or Control-It!, with denatonium. Some people also find that clear nail polish helps as a different type of reminder to give up the nail-biting habit.

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About the Author
Joe Graedon is a pharmacologist who has dedicated his career to making drug information understandable to consumers. His best-selling book, The People’s Pharmacy, was published in 1976 and led to a syndicated newspaper column, syndicated public radio show and web site. In 2006, Long Island University awarded him an honorary doctorate as “one of the country's leading drug experts for the consumer.”.
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  • Ershad M et al, "N-Acetylcysteine." StatPearls, Feb. 19, 2023.
  • Lee DK & Lipner SR, "The potential of N-acetylcysteine for treatment of trichotillomania, excoriation disorder, onychophagia, and onychotillomania: An updated literature review." International Journal of Environmental Research and Public Health, June 2022. DOI: 10.3390/ijerph19116370
  • Harlivasari AD et al, "The role of twice-daily N-acetylcysteine (NAC) 2400 mg in smoking cessation: A randomized, placebo-controlled trial in Indonesia." Cureus, Feb. 16, 2024. DOI: 10.7759/cureus.54322
  • Millea PJ, "N-acetylcysteine: multiple clinical applications." American Family Physician, Aug. 1, 2009.
  • Berk M et al, "Nail-biting stuff? The effect of N-acetyl cysteine on nail-biting." CNS Spectrums, Nov. 7, 2014. DOI: https://doi.org/10.1017/S1092852900023002
  • Ghanizadeh A et al, "N-acetylcysteine versus placebo for treating nail biting, a double blind randomized placebo controlled clinical trial." Anti-inflammatory & Anti-allergy Agents in Medicinal Chemistry, 2013. DOI: 10.2174/1871523011312030003
  • Skurya J et al, "Habit reversal therapy in the management of body focused repetitive behavior disorders." Dermatologic Therapy, Nov. 2020. DOI: 10.1111/dth.13811
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