NAIL BITING

Nail Biting – Can Science Help Us Quit?

“Do you have any habits like nail/pen/pencil/cheek/lip biting, resting your head on your hand, or habitual gum chewing?”

Researching and writing this nail biting article made my eyes go a little cross-eyed. Let me correct that—A LOT cross-eyed.

In this article, we are going to take a deep dive to uncover the psychology and nail anatomy behind nail biting to give you some insights on the best ways to overcome this painful, destructive and frustrating habit.

This article is broken down into three parts:

Part 1: The Research about Nail Biting

Part 2: The Function of Habit in Nail Biting

Part 3: Possible Solutions for Nail Biting

PART 1: The Research About Nail Biting

Since nail biting not discussed in my nail bible—Doug Schoon’s book (Nail Structure and Product Chemistry)—I needed to dust off my research skills from high school and college.

I poured through articles from PubMed, NCBI, Wikipedia, Iranian Journal of Medical Sciences, Brazilian Oral Research, Psychology Research and Behavior Management, Contemporary Clinical Dentistry, Journal of Psychiatry and Neuroscience and many others.

The biggest takeaway from all this research was a little bit of a disappointment.

There just aren’t enough studies about nail biting. It’s tough to really make solid conclusions.

A number of the hypotheses and research studies I read often contradicted each other.

The articles were littered with words like “suggested,” “suspected,” “controversies,” “contradictory reports,” “not clear,” and “speculation.”

Now how am I supposed to make sense out of all that?

The Purpose Behind Weird Habits

What I do know is that our behavioral habits serve a purpose.

All habits have consequences or results. Whether the consequence is good or bad, it’s up to us to continually decide which result we want.

For example, if you want to be healthy, you choose to eat well and exercise. The result is better health.

If you want to stay alive while driving your car, you choose to drive on the correct side of the road.

These examples might seem like easier choices than stopping nail biting. And this could be true.

Some of our habits we do without even noticing or paying attention.

Nail biting is one of those habits.

So, how do we change something we don’t even realize we’re doing?

Nail Biting: How To Get The Most Out of This Article

Today’s article is going to be filled with nitty gritty research article quotes.

After each quote, I offer a translation into something that’s easier to understand if you’re just looking for the important stuff.

This for those of you who just want the gist of the research. Just look for the sections titled “Ana’s Interpretation” with my photo.

Introduction

Onychophagia (AH-nih-koe-FAY-gia), defined as habitual nail biting, is a common disorder affecting 20-30% of the population and all age groups. It may lead to significant psychosocial problems, have a negative impact on quality of life, and cause complications involving both the nail unit and the oral cavity…Since onychophagia is a challenging disorder to treat, a multidisciplinary approach should be taken involving dermatologists, internists, pediatricians, psychiatrists, and dentists. ~PubMed

Ana’s Interpretation

The many causes for nail biting include stress, boredom, anxiety, depression, loneliness, heredity, imitation of a family member, prior thumb-sucking habit, inactivity, and poorly manicured nails.

You’ll see in the rest of this article that many of the negative attempts to help others don’t work. Punishment, nagging and threats, ridicule, and application of bitter tasting solutions really don’t work.

In many cases, these types of attempts can actually make the problem worse.

Treatment is most effective when directed at the root cause of the behavior.

For nail biters to change their behavior, they have to want to make the change.

Some Medical Definitions for Nail Biting

Definition

The operational definition of NB is “putting one or more fingers in the mouth and biting on the nail with teeth”.³ The habit of NB is often limited to fingernails, and most of the individuals with the habit do not have any preference for biting any of the fingernails. ⁴ This behavioral problem has been reported in children and adults.

Classification

Nail biting (NB) is not a pathological condition in all times and all clients. However, it is not exactly clear where the border between the healthy and unhealthy behavior of NB is. Nail biting in healthy children is temporary and does not last very long. The frequency, intensity, and duration of pathological NB are higher than those in normal individuals. Uncertainties for the distinction of pathological and nonpathological NB are also reflected in the classification of psychiatric disorders. While some behavioral problems such as trichotillomania (hair pulling) are classified as an impulse control disorder in Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV), NB is not classified in DSM-IV.⁶ Nail biting can also be classified as a self-injurious behavior such as pathological skin-picking or as a stereotypic movement disorder.⁵ Others believe that NB is a part of obsessive compulsive disorder spectrum.⁶

Ana’s Interpretation:

Nail biting isn’t always an obsessive or compulsive behavior. Many people outgrow it or are able to stop the habit.

Often times nail biting is a symptom of something bigger.

Nail biting could fall in the category of Impulse Control Disorder like compulsive hair pulling.

Many of us by now have been diagnosed with some sort mental disorder.

While some of the mental disorders are commonly known as depression and anxiety—nail biting can be a symptom of ADHD, OCD, ODD, and a host of other mental disorders.

Is Nail Biting Age Related?

Nail biting usually does not start until the age of three or four years.⁷There are contradictory reports about the prevalence of NB. The prevalence of NB increases from childhood to adolescence and then decreases in adulthood.⁷It is not clear what percentage of the children with NB behavior stops it, and will not suffer from it later. Nail biting was not related to gender, conduct problems, inattentiveness, hyperactivity, and peer problems.

Ana’s Interpretation:

Usually, nail biting starts during childhood and is outgrown. For some people though, the behavior continues into adulthood. It’s really not understood why.

Nail biting isn’t exclusive to gender, certain conduct issues, lack of attention, hyperactivity or struggles with other students or co-workers.

It seems that most of the studies have been done with children. I’m not sure why. Perhaps it’s because it’s easier to gather data from them quickly. It’s also possible that children don’t have the additional work and relationship stress factors that adults have.

I find it interesting that nail biting increases during adolescence but supposedly isn’t related to peer problems.

Humm… Even though it’s been over 25 years since I attended high school, I’m pretty sure that it’s still riddled with cliques and peer problems.

Nail biting is probably because of rampant insecurity and self-loathing that is common among children.

Different stressors can certainly increase the intensity of a nail biting habit.

Epidemiological Factors

Epidemiology is the study and analysis of the patterns, causes, and effects of health and disease conditions in defined populations. It is the cornerstone of public health and shapes policy decisions and evidence-based practice by identifying risk factors for disease and targets for preventive health care. [Source: Wikipedia]

Connection between TMJ Disorder and Nail Biting

The rate of finger and nail biting in patients suffering temporomandibular joint pain and dysfunction was about 24.1%.⁸ Therefore, it is recommended to inquire about oral habits such as NB in all temporomandibular joint pain and dysfunction. Moreover, patients with temporomandibular joint pain and dysfunction should be consulted as part of their management.⁸

Ana’s Interpretation:

I wore braces twice to correct TMJ Disorder.

My jaw would lock shut or painfully pop while eating. I once dated someone who said I was a dainty eater. I had to take small bites because I could barely open my mouth!

My orthodontist told me to never chew gum and to wear my retainers every night for the rest of my life!

He said that the human jaw is not supposed to be constantly chewing.

This is why grinding teeth at night is also a problem. Biting nails can tire the jaw also.

E. Coli and Nail Biting

Oral habits like thumb sucking and nail biting are pernicious habits that act as an adaptive function in obtaining pleasure and subduing anxiety. These habits may also act as carriers of numerous microorganisms into the oral cavity, of which, Enterobacteriaceae members are transient pathogens, which might result in debilitating systemic conditions.¹⁰

The Enterobacteria species isolated in our study were E. coli, Klebsiella, Proteus, and Enterobacter. Of these, the most commonly isolated Enterobacteria among all three groups was E. coli (in 12 subjects), whereas the least isolated Enterobacteria was enterobacter (3 subjects). Our results are consistent with the results of Baydas et al. and Sushma et al.⁹ who showed a greater isolation of E. coli. Other organisms such as streptococci, staphylococci, pseudomonas, and candida were also seen along with Enterobacteria.

Literature revealed that environmental organisms can be inoculated into the oral cavity through paranormal habits like nail biting resulting in transmission of infections to other parts of the body, by contaminated hands or environmental objects, which may be responsible for the cause of morbidity and mortality worldwide.⁹

This indicates the greater prevalence of E. coli in humans among different population groups. Studies by earlier authors reported that E. coli were the most frequently isolated organism among Enterobacteriaceae family in different systemic illnesses. With these data, it can be suggested that E. coli gets a channel of entry into the oral cavity through the chronic nail biting and thumb sucking habits and can be a perpetrator of local and systemic infections.¹⁰

Ana’s Interpretation

Although it can calm anxiety, nail biting has a dirty little secret—you’re eating bacteria that can make you very sick.

The most common bacteria found is E. coli in research studies, but other organisms like strep, staph, pseudomonas, and candida were also found.

Unfortunately, bacteria don’t always die in the mouth. It can spread to your internal organs. Infections can lead to diseases and even death.

Nail Biting and E. Coli in Your Mouth

The Research Says:

The presence of a nail biting habit indicated a higher plaque index, which in turn showed a higher carriage of Enterobacteria spps, predominantly Escherichia coli.

Accumulating evidence suggests the impact of the dental diseases on the general health of the individual, warranting a harmonious relation of the microorganisms with that of the oral tissues, albeit any shift in this balanced ecology would unfold a series of events that might result in a disease status.¹⁰

Ana’s Interpretation:

People who bite their nails tend to have more plaque on their teeth, which makes a nice environment for E. coli to flourish.

Dental diseases can also mess with the good bacteria in your mouth.

Hand Washing

Here are some interesting statistics about hand washing. They’re pretty shocking.

While 62% of women are washing more than 10 times per day, only 37% of men are doing the same. 41% of men wash their hands 6 times a day or less, compared to only 17% of women. On average, American heads of household wash their hands 8.6 times per day (up from 8.0 in 2008).¹¹
In a survey of 100,000 people, which was the largest ever analysis into hand-washing, it revealed that 62% of men and 40% of women admit they don’t bother washing their hands after using the restroom.¹²
A study by the firm Initial Washroom Hygiene found that after using the restroom, a person has on average 200m bacteria per square inch on each hand. People can then transfer the bacteria to their hands or mouths, as well as onto doors, keyboards, phones. This means office workers come into contact with an average 10 million bacteria a day.¹³
Last year, US researchers highlighted the importance of hand washing, as it found a virus can spread through an office within two to four hours. Researchers found 40% to 60% of workers as well as visitors were infected after touching objects in the building.¹³

In the photo to the right, the green areas are the bacteria present on an average office keyboard.

Etiological Factors: The Contributing Causes of Nail Biting

(Etiology: the study of causation, or origination.)

The Research Says:

There are a lot of controversies about the causes of NB. While some studies related NB to behavioral problems,¹⁴ and anxiety,^15,16others did not believe so.^17,18Anxiety in children with NB is not a trait; it is a state.¹⁹

Although it was suggested that NB might reduce anxiety or tension,¹⁶ recent studies do not support the anxiety theory for NB.^1,20Nail biting usually occurs as a result of boredom or working on difficult problems rather than anxiety. Nail biters do not bite their nail when they are engaged in social interactions, or when they are reprimanded for the behavior.²⁰Nail biting occurs more often in boredom or frustration than in contingent or noncontingent attention in undergraduate students.²⁰It is suspected that smoking and gum chewing in adults are substitutes for NB in childhood.⁷Severe and mild NB appear to have some differences in terms of the basis of physical and social consequences, severity, frequency, and physiological mechanisms.²¹

Ana’s Interpretation:

Remember when I said that the various hypotheses and research studies contradict each other?

Above is a perfect example. Some studies say that behavior problems and anxiety cause nail biting. Others disagree.

I’ve interviewed a lot of people who said that anxiety is one of the main reasons causing them to bite their nails.

I don’t agree with the statement that boredom or working on difficult problems is the reason for biting over anxiety.

It’s thought that smoking and gum chewing in adults is replacing a childhood nail biting habit.

The research I reviewed indicated that people who were childhood biters who picked up smoking or chronic gum chewing were less likely to continue with nail biting.

Comorbidities or Underlying Conditions: What Else is Going On?

Definition of comorbidity: In medicine, comorbidity is the presence of one or more additional diseases or disorders occurring with (that is, concomitant or concurrent with) a primary disease or disorder; in the countable sense of the term, a comorbidity (plural comorbidities) is each additional disorder or disease. [Source: Wikipedia]

The Research Says:

There are limited reports about co-morbidity of NB with psychiatric disorders.² Three most common co-occurring psychiatric disorders in clinical sample children with NB are attention deficit hyperactivity disorder (74.6%), oppositional defiant disorder (36%), and separation anxiety disorder (20.6%).²

All of the boys and 81% of the girls of the clinical sample of children with NB suffer from at least one psychiatric disorder.²

The most common co-occurring stereotypic behaviors were lip biting (33.3%) and head banging (12.7%).² Another study reported that 70% of individuals with hair-pulling habit had other stereotypic behaviors, of which skin-picking and nail-biting were the most common ones.²²

Ana’s Interpretation:

There haven’t been many reports about the correlation between nail biting and mental disorders.

Attention deficit hyperactivity disorder (ADHD), oppositional defiant disorder (ODD), and separation anxiety disorder do seem to contribute to nail biting urges.

Interestingly, in one clinical sample, all of the boys and 81% of the girls with a mental disorder bite their nails.

The most common behaviors besides nail biting were lip biting, head banging, hair pulling and skin picking.

Family Matters: Psychiatric Disorders of Parents of Children with Nail Biting

The Research Says:

The only study that investigated the parents of children with NB reported that about 56.8% of mothers and 45.9% of fathers suffered from a psychiatric disorder, which most often was a major depressive disorder.²The rate of major depressive disorder in mothers was 46.6% and in fathers was 35.1%. A study on children of mothers with psychiatric disorders reported that the rate of NB in children of mothers with schizophrenia was more than that in children of mothers with bipolar disorder. Also, the rate of NB in children of mothers with schizophrenia or bipolar disorder was higher than that in the control group.²³

Overall, the reviewed literatures suggest that co-morbidities of psychiatric disorders and other stereotypic behaviors in a clinical sample of children with NB is more than 80%, and more than half of the parents suffer from psychiatric disorders mainly depression.³²

Ana’s Interpretation:

Only one study looked at the parents of nail biting children. Approximately 50% of mothers and fathers suffered from a mental disorder. Depression was most often reported.

Another study showed that the type of mental disorder in the mothers made a difference too. More children bite their nails if their mother has schizophrenia when compared mothers who have bipolar disorder.

Over 80% of the children in one clinical sample also had a mental disorder.

Nail Biting is a Family Issue

The Research Says:

Nail biting consequences are not limited to the afflicted individuals, and usually, have an impact on members of the family. Sometimes, the parents or other family members feel shame from the behavior of their children or siblings. The children or adults with NB might be laughed at or stigmatized by others. Nail biting may cause a restriction in social behaviors or behaviors that should be done in the presence of others using hands such as writing, drawing, or playing.³²

Children with NB are frequently attacked by others. Children with NB are usually told that they are able to control or stop NB, but they do not like to stop it. Attacks not only do not improve NB behavior but also can add more to the stress, frustration, helplessness, hopelessness, and anxiety of the children. In addition, nail biting has effects on the oral carriage of Enterobacteriaceae.³²

The rate of Enterobacteriaceae is more in the oral cavities of children with NB habit than those without it.²⁴The force of biting nails can be transferred to the root of teeth and lead to apical root resorption,²⁵alveolar destruction,⁷ malocclusions,²⁶temporomandibular disorders,²⁷and gum injuries.²⁸Moreover, nail biting may damage the tissue around the nail and lead to infection and teeth root damage.²⁹Furthermore, in severe cases, NB may damage the nail beds and cause the disappearing of nails.³⁰The growth of nails can be increased by NB.³¹The outcome of NB is not just limited to medical consequences. Nail biting also causes some negative social and psychological consequences for the patients and their parents.³²

Ana’s Interpretation:

Nail biting can have a significant impact on the rest of the family. Shame, ridicule, and isolation are very common.

Children are often attacked by others and told they can stop biting easily. This leads to more stress, frustration, helplessness, hopelessness, and anxiety.

Of course, as mentioned earlier in this article, the rate of germs and bacteria significantly increases with nail biting. It can cause teeth, gum, and joint injuries too.

Although damaging the nails by biting can actually speed nail growth, it’s inconsequential since the biter is causing more damage to the nail plate and nail bed.

Management and Treatment of Nail Biting

The Research Says:

Nail biting is a habit that cannot be managed without considering some related factors such as comorbidities, precedent, and consequences of the behavior.

Any treatment should be accompanied by educating the afflicted children as well as their parents, siblings, and teachers. They should be taught about what to do and what not to do about it. For example, they should know that punishment, threat or laugh at the children with NB can increase this behavior, because they try to catch others’ attention by NB. Sometimes, the parents feel guilty for their children NB habits. These feelings should be detected and managed. Siblings may feel shame for to their brothers’ or sisters’ NB behavior. So, they need to be included and educated in the process of management as well. Coating nails with unpleasant materials or covering them are tried by many parents, but it is usually ineffective. Others should not blame children with NB habit and increase their disappointments, instead, they should encourage them, and give them support and confidence. The management and treatment of a child with NB behavior will not happen in a few sessions, it is a long process. All of such clinical findings indicate that the management of NB is much more complicated than just focusing on its stoppage. Treatment is not as easy as it seems. Because NB can damage teeth and alveolar structure, the afflicted children should be referred for the assessment and management of possible damages.

There are some methods suggested for controlling of NB such as chewing gum or wearing a rubber piece on the wrist. However, these approaches need to be studied in control trials for their efficacy. Also, the efficacy of engaging fingers with substitute activities such as writing, drawing, holding small balls, or musical instrument should be investigated.³²

Ana’s Interpretation:

Before the nail biting habit can be managed, it’s important to look at why you do it.

Is it a life long issue?
Are mental health issues contributing?
And ultimately, how does the behavior make you feel?

Treatments need to be accompanied with compassion. Punishment and ridicule are more likely to increase biting rather than resolve it.

Parents, siblings, and teachers need to be educated in how to support the nail biter to replace the biting behavior with a more positive behavior.

Coating nails with bitter products usually doesn’t work and learning to manage the behavior takes time.

Treatment is not as easy as it might seem.

As of this writing in 2017, conclusive studies don’t exist.

There have been suggestions for controlling nail biting by looking at the use of chewing gum, wearing a rubber band around the wrist, or keeping hands occupied with something.

Psychotherapy

The definition of psychotherapy is the treatment of mental disorder by psychological rather than medical means.

The Research Says:

There are limited controlled clinical studies on behavioral or psychotherapeutic approaches to the treatment of NB. There are some cognitive behavioral techniques for the management of children’s behaviors. These techniques have many similarities and are based on cognitive and behavioral principles such as learning principles. All of them teach some skills to the children to be able to control NB behaviors. Patients with NB habit can be trained for different types of relaxations such as self-statements of relaxation, visual imagination, muscle relaxation, and deep breathing.³²

Ana’s Interpretation:

There are very few controlled studies that look at behavioral treatment for nail biting.

Adults can be more successful learning different types of relaxation techniques.

Whereas, it’s much more difficult for children to embrace the brain training required to stop an unconscious behavior.

My boys, Mr. D and Mr. B, have ADHD and ADD respectively.

They can’t stand going to the psychiatrist for their medical checkups—and those are only 15 minutes!

Most kids would rather be riding their bikes, playing video games, or other fun activities.

They don’t want to sit on a couch talking to a therapist about why they bite their nails.

Part 2: The Function of Habit in Nail Biting

Functional Assessment Analysis

Nail biting can be a learned behavior according to a cognitive model. In this model, positive, negative, or automatic reinforcement maintains our habits. So, our habits have functions.³²

Ana’s Interpretation:

It’s important to note that it’s pretty much impossible to “break” a bad habit (a little more research about this later).

So if you’re trying to quit a habit like biting your nails, smoking, or reaching for a pint of Ben and Jerry’s when you’re stressed, quitting cold turkey is not going to set you up for success.

Well meaning people and medical professionals will tell you that you just need to develop more “willpower”. They think that willpower will be strong enough to overcome a bad habit.

And if you lack strong enough willpower, that deficiency is often viewed as a character flaw. Sadly, this makes you feel like a bad person.

Well, that’s not how the brain works.

Here’s a look behind the scenes of what makes a habit so hard to break.

Why We Have Habits

Habits are as much a part of our daily survival as oxygen.

We have so much information coming at us all day, every day, it’s impossible for our brains to process all of the new sensory input while we go about all our normal daily activities.

Habits are what allow our brains to put certain important routines on “autopilot” so we can deal with the next thing that comes our way.

Some examples of these helpful “autopilot” habits would include:

- Your morning routine of getting up, getting dressed, brushing your teeth, etc.

- Being able to drive to work without really paying attention to your route.

Riding a bike or touch typing on your computer without looking at the keys.

Taking the Highway or Surface Streets?

Once you’ve developed these routines/autopilot habits, they create a solid set of neural pathways in your brain.

This might seem like a weird exercise, but imagine your neural pathways like a huge 6-lane highway.

The 6-lane highway is the easy way to get where you’re going. Your brain is always looking for the easiest way to get things done.

When you try and go “cold turkey” to break a habit, it’s a bit like taking surface streets and trying to pretend the 6-lane highway doesn’t exist anymore.

Even if you don’t use the highway for years, it’s still there.

Your brains’ neural pathways have created a well-beaten path that won’t ever really go away.

It’s always easy to get back on that bad habit neural pathway. This is why it’s so easy to relapse in your habit-breaking quests.

An example of this alcoholics or others who struggle with addictions.

It’s so easy to relapse without a good support system and plans in place for different routines when these people experience triggers that they used to associate with drinking.

So, if you can’t break a habit, what do you do with it?

The better solution is to replace the routine or action you take when you’re triggered to bite your nails.

The Parts of a Habit

According to Charles Duhigg, author of The Power of Habit, there are three parts of a habit:

1. The trigger

1. The action or routine

The reward

These are the key components of how your brain is able to use these “autopilot habits.”

For example, your morning routine is triggered by your alarm clock going off (this is an external environmental trigger). Your brain has learned to associate the alarm clock with all the steps you take to get out the door (the routine).

Your brain gets a nice brain boost of chemicals that give you a sense of achievement when you complete the action of the habit. This is the reward.

This autopilot habit process works the same for good habits and bad habits. Let’s look at how it works in a nail biting scenario.

1. The TRIGGER: Can be internal (stress, boredom, etc.) or external (rough skin, peeling or jagged nails, etc.).

1. The ACTION or routine: Biting or picking at your nails.

The REWARD: Sense of completion from performing your bite/pick habit, even if it’s the sting of nails bitten to short or skin picked at until raw and bleeding.

Author Marshall Goldsmith adds to Duhigg’s 3-part habit loop in his book Triggers, by breaking down step the process into 4 steps, adding a step between the trigger and the routine: IMPULSE.

The impulse is where your brain automatically analyzes your trigger and does its best to “help” you get to your reward.

Your brain plugs in a routine that it is familiar with and associates with a reward. This association is built through doing the same routine over and over.

When you’re able to help your brain become conscious of your trigger and the following impulse, you’re able to consciously change the routine you take to get the reward. This helps you get the results you want.

Let’s look a little deeper into what research says about habits…

Habit Reversal

The Research Says:

Some authors believe that NB is a learned habit, rather than an emotional condition.²⁹Habit reversal is a form of behavioral therapy, which uses a similar or dissimilar competing response.³²

Ana’s Interpretation:

Like I mentioned before, habits can’t be broken.

Habits have to be replaced with another behavior that is incompatible with the first behavior (remember the 6-lane highway analogy above?).

This process is called competitive response training. This is the fancy label for “replace the bad behavior with a good behavior.

Awareness

The Research Says:

The recording of NB frequency, videotaping of NB behavior and describing its frequencies increase awareness. Its frequency should be recorded on a card. It will help children to monitor their behavioral changes. Situation awareness is the type of awareness that children with NB habit identify the situations or places in which NB is better or worse.³²

Ana’s Interpretation:

It’s a pain in the “you know what”, but it is a good exercise to write down the times you catch yourself biting. Perhaps you could use the notepad application on your phone.

Record what you’re feeling at the moment and where you are. If you’re helping a child, with permission they may be open to you videotaping the behavior.

The Research Says:

For competitive response training, a behavioral pattern that is incompatible with NB is introduced. Competing responses should be contingent with NB. There are different types of contingency management. Parents can comment on improvement of the behavior, and provide some praise for the improved child. For example, the child can go to some places or enjoy activities that he/she has been avoided before. Competing responses should be practiced every day. Parents should encourage children with NB habit using competing response. Behavioral changes are long processes, and parents and their children should be informed that they will not happen over a few days or weeks. This is very important because parents or children usually give up soon.³²

Ana’s Interpretation:

Let’s look at the definition of contingency. It is the relationship between two events, one being “contingent on” or a consequence of the other event.

Here is a real life example of contingency. My son, Mr. D, wanted to stop biting his nails. My agreement with him was to purchase a coveted Lego^® set if he went for 3 weeks without biting.

He held out until he earned the reward and then relapsed.

About a week later he said, “Mom if I go without biting my nails for 3 weeks again, can I get another Lego^®set?” Ah, the creativity of children!

The research suggests that competing response should be practiced every day. That leads us to the next section. Does doing something else at the time of biting help at all?

Habit Reversal Versus Object Manipulation

Pro Habit Reversal

The Research Says:

The current study investigates the efficacy of habit reversal training (HRT) and compares its effect with object manipulation training (OMT) considering the limitations of the current literature.

There was three groups of Habit Reversal Treatment group (HR) (n = 30), Object manipulation group (n = 30), and wait-list or control group (n = 31) in this study. All the three groups were assessed at baseline. However, both HR and Object manipulation groups received intervention while the wait-list group did not receive any intervention.³³

Habit Reversal (HR)

HR treatment was conducted according to a protocol provided by Woods.³⁵ In this protocol, the possible functions of nail biting as well as the feelings experienced before, during and after nail biting were identified. According to this protocol, habit reversal includes awareness training, competing response training, and social support training. These trainings were conducted in a 30-minute session. In fact, the next sessions were booster sessions to monitor the progress and develop solutions to problems which occurred during the implementation of the intervention. In awareness training, children were trained to recognize their nail biting behavior and its warning signs. For competing response, children were trained to exhibit a behavior which was incompatible with nail biting immediately after the occurrence of nail biting or one of its warning signs. They were asked to hold a pencil or a toy with their hands. Finally, a person was identified to support children to increase their treatment compliance, and remind their competing response, and reward them for their compliance.³³

Ana’s Interpretation:

Some authors believe that nail biting is not related to an emotional condition, but rather a learned habit.

Habit reversal is a form of behavior therapy, which uses a dissimilar or similar competing response.

For the habit reversal research group, training included:

1. Awareness Training: how to recognize the biting behavior and warning signs.

1. Competing Response: choose a behavior which was incompatible with nail biting, like holding a pencil or toy.

Social Support Training: another child in the study was assigned to hopefully help improve success.

Let’s look at different possible solutions to help replace the nail biting habit.

Part 3: Possible Solutions for Nail Biting

Object Manipulation (OM)

The Research Says:

[The object manipulation] group of children was trained for all the items reported for HR training. They were trained to play with something (such as a toy, pencil) instead of biting their nail. In fact, nail biting was replaced by playing with something. All other parts including awareness training and social support were similar to habit reversal treatment group. In fact, the object manipulation condition and HR condition were identical. However, children in object manipulation condition manipulated an object instead of doing a competing response.³³

Ana’s Interpretation:

The object manipulation group was trained the three techniques like the HR training group. The only difference was that the competing response was to play or “fidget” with something rather than just hold it.

The Research Says:

Overall, the current results confirmed that HR significantly increases the mean length of nails more than the other two groups in long term. This confirms that HR is an effective treatment for the management of nail biting for the community sample -of children and adolescents. Moreover, nail length increased during the trial in both groups of intervention while the mean length of nails in the wait-list group decreased during the trial. It is consistent with and supports the results of Woods et al.’s study.³⁴ However, there is a lot of covariate factors considered in the current study that were not considered in the study by Woods et al. (1999). Moreover, the study by Woods et al. (1999) was conducted on children with thumb sucking. Only some of their participants had nail biting problem. In addition, we did not find any study on the effect of object manipulation on nail biting behavior. Therefore, the current study seems to be unique.

Regarding our second aim, the obtained results showed that object manipulation was more effective than wait-list in short term. Moreover, object manipulation significantly decreased nail biting in long term. However, the number of children who completely stopped nail biting was very close to each other. Therefore, further studies with longer duration are recommended.

Our third aim was to compare the effectiveness of object manipulation training and habit reversal training. The results showed that, in long term, both object manipulation training and habit reversal training are significantly effective for treating nail biting behavior. However, habit reversal training is more effective than object manipulation training.

Concerning our aim to understand the acceptability of object manipulation training and habit reversal training, the current results showed no significant difference between the two groups regarding their acceptability.

However, the drop-out rate was higher in the object manipulation group than the habit reversal group.

In conclusion, habit reversal more than object manipulation increases the mean length of nails in long term.³³

Ana’s Interpretation:

Interestingly, the act of holding an object—versus fidgeting with it—was more successful this study—in increasing the mean length of nails.

Also, the drop-out rate was higher with the object manipulation group.

Isn’t that interesting?

Perhaps the participants were starting to feel that it wasn’t working well enough.

Competing Response

The Research Says:

In this behavioral method, the subject performs a competing response whenever he/she has the urge to bite or finds his/hers biting nails. For example, a behavior to stop or avoid moving upper limbs towards face or lips, or a behavior to stop or inhibit entering fingers into the mouth is employed. This method has been shown to be more effective than not using it.²⁹Competing response type is not important for the suppression of target behavior, and it does not probably function as an incompatible behavior.³⁵

Ana’s Interpretation:

Like mentioned before, competing response means to do a behavior that makes it difficult to bite.

A good example of this is to stick your hands in your pockets when tempted to bite. Studies have shown that this technique works better than not using it.

The only problem is that we can’t keep our hands in our pockets all the time.

And ultimately, the competing response doesn’t stop the desire to bite.

Aversive Stimulus

The Research Says:

An aversive stimulus is effective for treating NB and is usually done through the painting of an aversive stimulus or a bitter substance on the individual nails. Aversive stimulus therapy improves NB, although its effect is not as much as the competing response method.²⁹

Ana’s Interpretation:

Aversive stimulus means to apply some sort of negative reinforcement. The classic solution is to paint a bitter solution on the nails.

Unfortunately, this works for a very short time and could go the other direction if the person actually becomes accustomed to the bitter solution painted on their nails.

Punishment or ridicule also falls in this category. It’s been proven in many studies to not work, and can even increase the behavior.

Self-Control Intervention

The Research Says:

Considering that human behavior is goal-directed and affected by different factors, self- control intervention is proposed as a method for the management of NB.³⁶In this method, some specific self-control skills are learned and applied by the subjects. The method is performed in a number of steps. First, the children are taught that the targeted behavior is a problem, and they can change it. Second, the children are told to try to find the possible cause of NB as well as the thought and feelings that are associated with the behavior. Third, the children are instructed to do self-monitoring, as it can increase their awareness from the behavior. Fourth, children are educated to use some learned skills such as self-talk and self-reward to change the automated behavior. Fifth, children are trained to use the learned skills to manage and change other similar pathologic behaviors.³⁶

Ana’s Interpretation:

Human behavior is affected by many different things and is goal directed. If we want something, then we want it.

In one study, children were taught to realize that biting is a problem that they can change, and find the cause and feelings related to biting.

The children were asked to do self-observation, then use learned skills like self-talk and self-reward which would help them manage and change their behavior.

These trained behaviors are hard enough for adults to use, let alone children.

“Self-control” is something to me that is said by someone who doesn’t really understand the new research of how behavior works.

That’s like saying “don’t have that piece of cake because the sugar will make you feel horrible and can contribute to weight gain.”

Who cares? If we want cake, then we get an IMMEDIATE reward.

If we want cake, then we get an IMMEDIATE reward.

Or how about this one? “The solution is easy. Just stop biting your nails.” Except that for most people who are nail biters is that they don’t even know they are doing it.

Nail biting has moved beyond a chosen behavior to one that is unconscious.

Pharmacotherapy

As most of my readers know, I try to stay away from medical and pharmaceutical discussions as much as possible.

There is so much misinformation on the internet which is completely false and downright scary.

I also have no right making any medical claims or advice. That is something reserved for your doctor.

With that being said, I feel I would be remiss in not including studies that have included using medications and alternative pharmacological treatments to help with nail biting.

These are definitely things you will want to discuss with your doctors. Feel free to print or email this article to take to your doctor.

Prescriptions

There are several pharmaceutical drugs that have had some success with nail biting.

There is also the factor that all of our bodies are different and react differently to various medications and alternative remedies.

In fact, some medications like selective serotonin reuptake inhibitors (SSRI’s) may make nail biting worse.

There seems to be an interesting correlation in which drugs work better with people with obsessive compulsive disorder (OCD). Some researchers feel that nail biting, hair pulling, and OCD all have similar causes.

The Research Says:

It is supposed that NB, trichotillomania, and obsessive-compulsive disorder have a similar biologic etiology.³⁷

Since NB is an impulse disorder, selective serotonin reuptake inhibitors (SSRIs) may exacerbate it. This suggestion is based on the belief that impulsivity is exacerbated in some impulse-prone patients by SSRIs.³⁸

As of 2011, and to the best of the author’s knowledge, there is no double-blind, placebo-controlled trial investigating the efficacy of drugs such as fluoxetine and fluvoxamine for the treatment of NB. There are just a number of case reports about the association of NB with other similar behaviors such as skin picking. Fluoxetine has been reported to be effective for the treatment of chewing of digits.³⁹ A double-blind comparison of clomipramine and desipramine effects in individuals with NB habit, who did not have obsessive compulsive disorder, indicated that clomipramine was more effective than desipramine.³⁷

Fluoxetine (floo OX e teen)

Brand Names: PROzac, PROzac Weekly, Sarafem, Rapiflux, Selfemra, PROzac Pulvules. Fluoxetine is a selective serotonin reuptake inhibitors (SSRI) antidepressant. Fluoxetine affects chemicals in the brain that may be unbalanced in people with depression, panic, anxiety, or obsessive-compulsive symptoms, bulimia nervosa (an eating disorder), obsessive-compulsive disorder, panic disorder, and premenstrual dysphoric disorder (PMDD). [Source: Drugs.com]

Fluvoxamine (floo-VOX-a-meen)

Brand Names: Faverin, Fevarin, Floxyfral, Dumyrox and Luvox. Fluvoxamine is a medication which functions as a selective serotonin reuptake inhibitor (SSRI) and receptor-agonist. Fluvoxamine is used primarily for the treatment of obsessive–compulsive disorder (OCD), and is also used to treat major depressive disorder and anxiety disorders such as panic disorder and post-traumatic stress disorder. Fluvoxamine CR (controlled release) is approved to treat social anxiety disorder. [Source: Wikipedia.org]

Clomipramine (Clo-mi-pram-mine)
Brand Name: Anafranil. Clomipramine is a tricyclic antidepressant (TCA).^[2] It is used for the treatment of obsessive compulsive disorder, panic disorder, major depressive disorder, and chronic pain. [Source: Wikipedia.org]

Desipramine (also known as desmethyl-imipramine)
Brand Names: Norpramin, and Pertofrane. Desipramine is a tricyclic antidepressant (TCA). It inhibits the reuptake of norepinephrine and to a minor extent serotonin. It is used to treat depression, but not considered a first line treatment since the introduction of SSRI antidepressants. [Source: En.Wikipedia.org]

Alternative Pharmacological Treatments

Two medication alternatives that might show promise are Glutamate and N-acetylcysteine.

For those of you who want to stay away from pharmaceutical medications, these are worth discussing with your doctor or psychiatrist.

The Research Says:

Glutamate

Glutamate, an excitatory central nervous system neurotransmitter, is emerging as a potential alternative pharmacological treatment when compared to gamma-aminobutyric acid (GABA)-, dopamine-, and serotonin-modulating treatments for neuropsychiatric conditions. The pathophysiology, animal models, and clinical trials of glutamate modulation are explored in disorders with underlying inhibitory deficits (cognitive, motor, behavioral) including obsessive–compulsive disorder, attention deficit hyperactivity disorder, Tourette syndrome, trichotillomania, excoriation disorder, and nail biting. Obsessive–compulsive disorder, attention deficit hyperactivity disorder, and grooming disorders (trichotillomania and excoriation disorder) have emerging positive data, although only scarce controlled trials are available.⁴⁰ CNS homeostasis of inhibition–disinhibition signaling ultimately depends on a well-regulated glutamate–GABA balance, in conjunction with other neurotransmitter systems that impact on this final effector pathway, which highly impacts neuronal health.⁴¹

Future drug design approaches will benefit from a better understanding of these pathways (which also impact on other biologic systems, including immune and developmental networks) in OCD and related disorders, tics and ADHD, in order to provide a paradigmatic framework to better understand the imbalance in inhibition–disinhibition from the molecular level (glutamate–GABA) to the macro-behavioral level (obsessions, compulsions, tics, hyperactivity, and grooming behaviors). The heuristic value of considering these cross-disorder clinical manifestations in toto in relation to glutamate awaits future drug discovery to address these disinhibitory phenomena. In summary, drugs that impact the glutamatergic balance in the CNS are emerging as a therapeutic alternative for neuropsychiatric disorders, which implicate abnormal inhibitory control in cognitive, motor, behavioral, and grooming domains. OCD has the most support at present for the use of glutamate modulators, with ADHD and grooming disorders also showing promise.⁴⁰

N-acetylcysteine

N-acetylcysteine (NAC) is emerging as a useful agent in the treatment of psychiatric disorders.

Quotes from the following article published in the Journal of Psychiatry and Neuroscience was recommended to me by my children’s psychiatrist.

The interesting thing to me is that he is a nail biter!

When I asked him what his triggers were, his response was “being caught in heavy traffic, watching movies and idleness”.

The Research Says:

Our review outlines the current literature regarding the use of N-acetylcysteine (NAC) in disorders including addiction, compulsive and grooming disorders, schizophrenia and bipolar disorder. N-acetylcysteine has shown promising results in populations with these disorders, including those in whom treatment efficacy has previously been limited. The therapeutic potential of this acetylated amino acid is beginning to emerge in the field of psychiatric research.⁴²

In addition to TTM (hair pulling), promising preliminary results suggest the need for controlled studies in other grooming disorders, including nail biting and skin picking.^43,44 A case report was published regarding an individual with both TTM and nail biting behaviours, in whom nail biting ceased following 9 weeks of NAC treatment.⁴³ The participant relapsed after a hiatus in treatment, but recommencement of NAC resulted in a remission of symptoms.⁴³

A serendipitous finding of the benefit of NAC treatment in the reduction of nail biting in a study primarily investigating NAC (2000 mg/d) in the treatment of mood disorders has been reported.⁴⁴

Three participants taking NAC reported significant reductions in nail biting during the 6-month course of treatment. All 3 participants were still abstinent from nail biting 1 month after the discontinuation of NAC.⁴²

Ana’s Interpretation

N-acetylcysteine (NAC) has shown promising results in populations with addiction, compulsive and grooming disorders, schizophrenia and bipolar disorder. It has been helpful for people who have tried other medications with no success.

The healing ability of this acetylated amino acid is beginning to emerge in the field of psychiatric research. We need more controlled studies to see if NAC works better than a placebo.

One study using NAC to treat mood disorders happened to reveal a side effect of reduced nail biting.

Three participants reported this during their 6-month treatment and after another month of stopping the NAC, they still were not biting. That is promising news!

Side Benefits?

Often times a drug that is formulated for one issue can actually have other side benefits—that make it sell even better than the original intent.

Here are a couple of examples of what I mean.

Propecia, that ubiquitous drug used to treat male-pattern baldness, was originally marketed as Proscar, a drug to treat the benign enlargement of the prostate. After five years on the market in the 1990s, it became clear that one of the side effects of Proscar was – you can practically see the money signs flashing in the pharmaceutical marketers’ eyes – hair growth on bald men. Cha-ching!⁴⁵

Listerine was invented 133 years ago, first as a surgical antiseptic, but also as a cure for gonorrhea (don’t try that at home). An article from 1888 recommends Listerine “for sweaty feet, and soft corns developing between the toes.” Over the course of the next century, it was marketed as a refreshing additive to cigarettes, a cure for the common cold, and as a dandruff treatment. But it was in the 1920s that the powerful, germ-killing liquid finally landed on its most lucrative use as a magical cure for bad breath.⁴⁵

Medical Advancements

The world of science and mental disorders is continually changing and making discoveries that can change our life for the better.

Think about how little we knew about the human body just 100 plus years ago. Here are some of the advancements we have made;

1901 Blood typing was established
1921 Discovery that the absence of vitamin D causes Rickets
1907 Blood transfusions started
1922 Insulin was first used to treat diabetes
1928 Discovery of penicillin
1930 Discovery of vitamins
1935 Invention of the Heart-Lung machine
1953 Heart-Lung machine used for the first time in surgery
1953 The DNA molecule was discovered
1967 The first human heart transplant was performed
1978 The first test tube baby was born
1996 Dolly the sheep became the first cloned mammal and lived for 7 years.⁴⁸

Other advancements that were life changing were the creation of vaccines starting in 1923 to the present, and their ability to prevent diseases like diphtheria, pertussis (whooping cough), tuberculosis, tetanus, influenza, polio, measles, mumps, etc. The list goes on and on. The discovery of anesthetics, clean water, and sanitation practices, and the creation of the birth control pill were also very important.⁴⁶

Mental Health Advancements

Although people have been living with mental health issues since the beginning of the human race, the Mental Health America (MHA) wasn’t founded until 1909.

Around the turn of the twentieth century, Clifford W. Beers, a recent graduate of Yale College and a newly-minted Wall Street financier, suffered his first episode of bipolar disorder (manic depressive illness) following the illness and death of his brother. In the throes of his illness, Beers attempted to take his own life by jumping out a third story window. Seriously injured but still alive, Beers ended up in public and private hospitals in Connecticut for the next three years.

While in these institutions, Beers learned firsthand of the deficiencies in care as well as the cruel and inhumane treatment people with mental illnesses received. He witnessed and experienced horrific abuse at the hands of his caretakers. At one point during his institutionalization, he was placed in a straight jacket for 21 consecutive nights.

Upon his release, Beers was resolved to expose the maltreatment of people with mental illnesses and to reform care. In 1908, he published his autobiography, A Mind That Found Itself, which roused the nation to the plight of people with mental illnesses and set a reform movement into motion. In the book, Beers declared, As I penetrated and conquered the mysteries of that dark side of my life, it no longer held any terror for me. I have decided to stand on my past and look the future in the face.⁴⁸

Ana’s Interpretation:

We have made significant progress over the last 100 years to identify and support people living with mental illnesses, but it’s still shocking how mental health is still such a taboo subject to talk about, even at the time of this writing in 2017.

This shame and fear make people feel very isolated and more inclined to resort to nail biting, skin picking, and hair pulling as a way to calm their anxiety.

Does that mean that everyone who bites their nails has a mental health disorder?

No, but it sure makes one think.

What if people are struggling with biting because it’s a symptom of something bigger?

There are so many working parts in the brain that depend on the environment, genetics, diet, personal history, current life situations, stressors, support systems and more.

Two different people could be struggling with biting and picking for completely different reasons.

It’s impossible to give a blanket conclusion that solves everyone’s problems because of these multiple layers of complexity.

One of the best ways to utilize all that we have learned in the past 100 years about mental health and physical health and different disorders is to begin to pay attention to YOU.

What works for you?
What doesn’t work for you?
What are your triggers?
What helps you overcome them?

If you don’t have the tools to overcome your triggers and other contributing issues, then you may find it helpful to enlist the help of a qualified physician, counselor, or other support groups.

I’ve started a Bliss Kiss™ support group on Facebook for people who struggle with biting and picking. [ myblisskiss.com/healthynails ]

Wherever you seek help, it’s important to find what works for you.

Find someone who understands you and can help you work through your unique situation.

Conclusion

As you can tell by now, a lot more studies need to be done to understand how to help someone stop biting their nails.

We need more randomized controlled clinical trials to make medication guidelines that are based on good evidence for the treatment of nail biting behavior.

Nail biting is not an isolated symptom.

Studies with children have shown that wearing nail coatings, repeated promptings to stop biting, and many behavior modification techniques don’t work because of the lack of consideration that nail biting might be a symptom for more complicated conditions.

Research studies become even more difficult when nail biting is a symptom of many different mental disorders.

It can be even harder to manage when someone has more than one disorder.

The great thing is that science keeps making advancements.

Society members around the world are using social media as a way to help reduce the stigma of mental health issues.

Online support groups are becoming very popular and available to anyone on the planet.

This is an exciting time in history for people from all over the world to support each other with our personal challenges.

We obtain a huge sense of connection and relief when we find other people who are struggling with the same issue. There are people out there who understand and support us. We no longer feel alone.

This is a very good thing.

References

Dufrene BA, Steuart Watson T, Kazmerski JS. Functional analysis and treatment of nail biting. Behav Modif. 2008;32:913–27. [PubMed]
Ghanizadeh A. Association of nail biting and psychiatric disorders in children and their parents in a psychiatrically referred sample of children. Child Adolesc Psychiatry Ment Health. 2008;2:13. [PMC free article] [PubMed]
Teng EJ, Woods DW, Twohig MP, Marcks BA. Body-focused repetitive behavior problems. Prevalence in a non-referred population and differences in perceived somatic activity. Behav Modif. 2002;26:340–60. [PubMed]
Leung AK, Robson WL. Nail Biting. Clin Pediatr (Phila) 1990;29:690–2. [PubMed]
Stein DJ, Simeon D. The nosology of compulsive skin picking. J Clin Psychiatry. 1999;60:618–9. [PubMed]
Pacan P, Grzesiak M, Reich A, Szepietowski JC. Onychophagia as a spectrum of obsessive-compulsive disorder. Acta Derm Venereol. 2009;89:278–80. [PubMed]
Tanaka OM, Vitral RW, Tanaka GY, et al. Nail Biting, or onychophagia: a special habit. Am J Orthod Dentofacial Orthop. 2008 Aug;134:305–8. [PubMed]
Saheeb BDO. Prevalence of oral and parafunctional habits in Nigerian patients suffering temporomandibular joint pain and dysfunction. Journal of Medicine and Biomedical Research. 2005;4:59–64.
Cohen MB. Etiology and mechanisms of acute infectious diarrhea in infants in the United States. J Pediatr. 1991;118:S34–9. [PubMed]

Firoz G. Kamal and Reginald Ajay Bernard. Influence of nail biting and finger sucking habits on the oral carriage of Enterobacteriaceae. Contemporary Clinical Dentistry.6(2); Apr-Jun 2015 PMC4456744
Echo Research. 2009 National Clean Hands Report Card® Survey Findings August 6-9, 2009. http://www.cleaninginstitute.org/clean_living/092109_summary.aspx
Madlen Davies. Do YOU always wash your hands after going to the loo? 62% of men and 40% of women admit they don’t bother. 27 February 27, 2015. http://www.dailymail.co.uk/health/article-2971931/Do-wash-hands-going-loo-62-men-40-women-admit-don-t-bother.html#ixzz4pxP8QebB
Madlen Davies. Do YOU always wash your hands after going to the loo? 62% of men and 40% of women admit they don’t bother. 27 February 27, 2015. http://www.dailymail.co.uk/health/article-2971931/Do-wash-hands-going-loo-62-men-40-women-admit-don-t-bother.html#ixzz4pxP8QebB
Ghanizadeh A. ADHD, bruxism and psychiatric disorders: does bruxism increase the chance of a comorbid psychiatric disorder in children with ADHD and their parents? Sleep Breath. 2008;12:375–80. [PubMed]
Joubert CE. Relationship of self-esteem, manifest anxiety, and obsessive-compulsiveness to personal habits. Psychol Rep. 1993;73:579–583. [PubMed]

Klatte KM, Deardorff PA. Nail-biting and manifest anxiety of adults. Psychol Rep. 1981;48:82. [PubMed]
Teng EJ, Woods DW, Marcks BA, Twohig MP. Body-focused repetitive behaviors: The proximal and distal effects of affective variables on behavioral expression. Journal of Psychopathology and Behavioral Assessment. 2004;26:55–64.
Friman PC, Larzelere R, Finney JW. Exploring the relationship between thumb-sucking and psychopathology. J Pediatr Psychol. 1994;19:431–41. [PubMed]
Gilleard E, Eskin M, Savasir B. Nail Biting and oral aggression in a Turkish student population. Br J Med Psychol. 1988;61:197–201. [PubMed]
Williams TI, Rose R, Chisholm S. What is the function of nail biting: an analog assessment study. Behav Res Ther. 2007;45:989–995. [PubMed]
Wells JH, Haines J, Williams CL, Brain KL. The self-mutilative nature of severe onychophagia: a comparison with self-cutting. Can J Psychiatry. 1999;44:40–7. [PubMed]
Stein DJ, Flessner CA, Franklin M, et al. Is trichotillomania a stereotypic movement disorder? An analysis of body-focused repetitive behaviors in people with hair-pulling. Ann Clin Psychiatry. 2008;20:194–8. [PubMed]
Vafaei B, Seidy A. A comparative study on the prevalence of emotional and behavioral symptoms in children and adolescents born to mothers with schizophrenia and other psychotic disorders. Acta Medica Iranica. 2003;41:254–9.
Baydas B, Uslu H, Yavuz I, Ceylan I, Dagsuyu IM. Effect of a chronic nail-biting habit on the oral carriage of Enterobacteriaceae. Oral Microbiol Immunol. 2007;22:1–4. [PubMed]
Odenrick L, Brattström V. The effect of nail biting on root resorption during orthodontic treatment. Eur J Orthod. 1983;5:185–8. [PubMed]
Oliveira AC, Paiva SM, Campos MR, Czeresnia D. Factors associated with malocclusions in children and adolescents with Down syndrome. Am J Orthod Dentofacial Orthop. 2008;133:1–8. [PubMed]
Winocur E, Littner D, Adams I, Gavish A. Oral habits and their association with signs and symptoms of temporomandibular disorders in adolescents: a gender comparison. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2006;102:482–7. [PubMed]
Krejci CB. Self-inflicted gingival injury due to habitual fingernail biting. J Periodontol. 2000;71:1029–31. [PubMed]
Silber KP, Haynes CE. Treating nail biting: a comparative analysis of mild aversion and competing response therapies. Behav Res Ther. 1992;30:15–22. [PubMed]
Lee DY. Chronic nail biting and irreversible shortening of the fingernails. J Eur Acad Dermatol Venereol. 2009;23:185. [PubMed]
Bean WB. Nail growth. Thirty-five years of observation. Arch Intern Med. 1980;140:73–6. [PubMed]

Ghanizadeh A. Nail biting; etiology, consequences, and management. Iran J Med Sci. 2011;36:73–79. [PMC free article] [PubMed]
Ahmad Ghanizadeh, Amir Bazrafshan, Ali Firoozabadi, and Gholamreza Dehbozorgi. Habit Reversal versus Object Manipulation Training for Treating Nail Biting: A Randomized Controlled Clinical Trial.l Iran J Psychiatry. 2013 Jun; 8(2): 61–67.
Woods DW, Murray LK, Fuqua RW, Seif TA, Boyer LJ, Siah A. Comparing the Effectiveness of Similar and Dissimilar Competing Responses in Evaluating the Habit Reversal Treatment for Oral-Digital Habits in Children. Journal of behavior therapy and experimental psychiatry. 1999;30:289–300. [PubMed]
Woods DW, Miltenberger RG. Tic Disorders, trichotillomania, and other repetitive behavior disorders. behavioral approaches to analysis and treatment. USA: Springer; 2006.
Ronen T, Rosenbaum M. Helping Children to Help Themselves: A Case Study of Enuresis and Nail Biting. Research on Social Work Practice. 2001;11:338–56.
Leonard HL, Lenane MC, Swedo SE, Rettew DC, Rapoport JL. A double-blind comparison of clomipramine and desipramine treatment of severe onychophagia (nail biting) Arch Gen Psychiatry. 1991;48:821–7. [PubMed]
Kindler S, Dannon PN, Iancu I, Sasson Y, Zohar J. Emergence of kleptomania during treatment for depression with serotonin selective reuptake inhibitors. Clin Neuropharmacol. 1997;20:126–9. [PubMed]
Velazquez L, Ward-Chene L, Loosigian SR. Fluoxetine in the treatment of self-mutilating behavior. J Am Acad Child Adolesc Psychiatry. 2000;39:812–4. [PubMed]
Marco A Grados, Elizabeth B Atkins, Gabriela I Kovacikova, and Erin McVicar. A selective review of glutamate pharmacological therapy in obsessive–compulsive and related disorders. Psychology Research and Behavior Management 2015:8 115-131. PMC4425334

Rothman SM, Mattson MP. Activity-dependent, stress-responsive BDNF signaling and the quest for optimal brain health and resilience throughout the lifespan. Neuroscience. 2013;239:228–240. [PMC free article] [PubMed]
Olivia Dean, Frank Giorlando, and Michael Berk. N-acetylcysteine in psychiatry: current therapeutic evidence and potential mechanisms of action. 2011. PMC3044191
Odlaug BL, Grant JE. N-acetyl cysteine in the treatment of grooming disorders. J Clin Psychopharmacol. 2007;27:227–9. [PubMed]
Berk M, Jeavons S, Dean O, et al. Nail-biting stuff? The effect of N-acetyl cysteine on nail-biting. CNS Spectr. 2009;14:357–60. [PubMed]
Haley Edwards, MentalFloss.com JANUARY 26, 2012 http://mentalfloss.com/article/29840/6-hugely-successful-products-originally-invented-something-else
Sept. 2112. https://health.wikinut.com/Medical-Advances-of-the-Last-100-Years/6j76joph/
Dan Childs, Susan Kansagra, et al. ABC News, Sept. 20, 2007 http://abcnews.go.com/Health/TenWays/story?id=3605442&page=
Source: http://www.mentalhealthamerica.net/our-history