Have you ever wondered why your fingers automatically find their way into your mouth without you even realizing it?

Well, you might be one of the millions who suffer from onychophagia. 

According to National Center for Biotechnology Information,“Onychophagia is defined as chronic nail biting behavior, which usually starts during childhood.”

While nail biting is a habit more common in children than adults, there are people who retain the habit even beyond the age of 18 years.

For example, clichéd as it may sound, the phenomenon is often seen in adults (often involuntarily) while watching horror or thriller movies.

Explaining why adults tend to often bite their nails, psychologist and author of “Obsessive-Compulsive Disorders: A Complete Guide To Getting Well And Staying Well,” Fred Penzel, told International Business Times: “People do these things as a way of managing levels of stimulation within their nervous systems.  They do these behaviors when they are either over-stimulated (stressed or excited) or under-stimulated (bored or sedentary).”

“When under-stimulated, the behavior provides stimulation to the nervous system and when over-stimulated, it reduces stimulation by getting people to focus down on what they are doing, to the exclusion of other things, and can have a kind of meditative effect,” Penzel added.

Nail Biting While nail biting is a habit more common in children than adults, there are people who retain the habit even beyond the age of 18. In this photo, Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge during the match between Andy Murray of Great Britain and Nicolas Almagro of Spain in the Quarterfinal of Men's Singles Tennis on Day 6 of the London 2012 Olympic Games at Wimbledon in London, England, Aug. 2, 2012. Photo: Getty Images/ Pascal Le Segretain

In a 2014 study, which interviewed 339 young adults, it was found that 46.9 percent of participants suffered from onychophagia and 0.9 percent had onychotillomania, a compulsive neurosis in which a person picks constantly at the nails or tries to tear them off.

Of those who were found to have onychophagia, 92.2 percent participant described nail biting as an automatic behavior.

Around 66 percent of nail biters reported feeling tension before biting their nails while, by 42 percent took pleasure from the act of nail biting. Among the participants with lifetime onychophagia, 22.5 percent were detected with a history of anxiety disorder and 3.1 percent suffered from OCD.

Despite this, the study did not find any definite links between OCD and nail biting.

This is why Penzel considers nail biting “an obsessive-compulsive related disorder” or “body-focused repetitive behaviors” – patterns of behavior that also include “hair-pulling and skin-picking.”

According to the TLC foundation, “Body-focused repetitive behavior (BFRB) is a general term for a group of related disorders that includes hair pulling, skin picking, and nail biting.  These behaviors are not habits or tics; rather, they are complex disorders that cause people to repeatedly touch their hair and body in ways that result in physical damage.”

Nail Biting Nail biting can be disease-causing bacteria and an array of germs being transferred into one’s body. In this photo, Barcelona's Argentinian forward Lionel Messi takes part in a training session at the Camp Nou stadium in Barcelona on April 5, 2011. Photo: Getty Images/ LLUIS GENE

There is one vital difference in behavioral patterns between people with OCD and people who are in the habit if biting their nails, according to Carol Mathews, a psychiatrist at the University of California, San Francisco, NPR reported. It is the fact that while the former act out of fear, the latter derive pleasure out of it.

OCD patient operate under a constant nagging feeling that if they do not arrange their clothes in a certain way or wash their hands at a certain time, something bad will happen to them. On the other hand, for people who bite their nails, "It's rewarding. It feels good. When you get the right nail, it feels good. It's kind of a funny sense of reward, but it's a reward," Mathews said.

According to Mercola, some of the harmful effects of nail-biting can be disease-causing bacteria and an array of germs being transferred into one’s body, paronychia (a skin infection caused by bacteria, yeast, and other microorganisms entering the damaged cuticles surrounding the nails), warts on one’s fingers caused by human papillomavirus, dental problems and impaired quality of life.

Penzel told IBT that while some easy-to-do tricks can be tried out for people who are not chronic nail biters, psychological therapy might be required for some, for whom it is a serious issue.

“In mild cases, doing things to retrain yourself over time, such things as chewing gum, covering your fingertips with tape, bandaids, or gloves, or finding small stimulating objects to manipulate can help,” Penzel said.

“In serious cases, it requires a form of comprehensive behavior therapy that helps the person identify all the various inputs and triggers that lead up to performing and maintaining the behavior, and then coming up with tactics to modify or control these things.”