Onychophagia
Nail biting is the habit of biting one's fingernails or toenails during periods of nervousness, stress, hunger, or boredom . It can also be a sign of mental or emotional disorder. It can be obsessive compulsive or can even be a completely unconscious act where the affected person is not or barely aware of the behavior whilst performing it. It has been documented that some people bite their nails in their sleep, sometimes exclusively. This has been linked to stress while dreaming or stress from the dream, or simply stress in general. It is considered to be the most widespread form of mild self mutilation. According to Freudian theory, nail biting is a symptom of oral fixation. The clinical name for nail biting is chronic onychophagia.
It occurs in:
- 28% to 33% of children ages 7-10 years old,
- 44% of adolescents,
- 19% to 29% of young adults and
- 5% of older adults

# Negative effects
Nail biting may result in the transportation of bacteria that are buried under the surface of the nail that are hard to clean and easy to get in the mouth. Likewise, broken skin on the cuticle may be susceptible to microbial and viral infections. These pathogens can be spread between digits via saliva.
Extreme nailbiting can be considered to be a form of masochistic self-mutilation. Bitten fingertips can become very sensitive to pain, usually at the place the skin meets the edge of the nail.

# Nail Biting and IQ
Studies by Russian researchers on children living in the Ural mountains region have found that nail biting may be contributing to the loss of IQ due to lead poisoning.  This is specially true among children who are still mentally developing.  Nail biters who work with iron (plumbers, painters or printers) may also be susceptible to poisoning in a similar way.

# Treatment
Causes of fingernail Biting

## Behavioral therapy
Some patients have found behavioral therapy to be beneficial on its own or as a complement to medication.  The first part of nail biting therapy consists of Habit Reversal Training (HRT), a four part process that seeks to "unlearn" the habit of nail biting and possibly replace it with a more constructive habit.  In addition to HRT, stimulus control therapy is used to both identify and then eliminate the stimulus that frequently triggers biting urges.
One might also use a mouthpiece to prevent the bite.  This can be found at nailbitestopper.com
The symptoms have been found to respond best to a combination of medication and therapy.

## Medication
Nail biting has been shown to respond well to certain types of medication.  The medications used to treat the problem include the newest, most potent anti-depressants. These medications are also used to treat Trichotillomania and OCD and include clomipramine, fluoxetine, sertraline, paroxetine, fluvoxamine, citalopram, escitalopram, nefazodone and venlafaxine.  Also, small amounts of the anti-psychotics used to treat schizophrenia such as risperidone, olazapine, quetiapine, ziprasidone, and aripiprazole can be used to augment anti-depressants. It is important to note that the use of anti-psychotics to treat nail biting does not necessarily indicate that the patient is suffering  from psychosis.