Nail-biting is regarded as a bad habit at the best of the times and a form of addiction at worst.
Despite the social implications and potential health consequences, over 30 per cent of people do it. So just what leads someone to habitually chew on the ends of their digits?
According to research, there are four main reasons why people bite their nails:
It feels good
A professor of psychology at UCSF (University of California, San Fransico), Tracy Foose, says it feels "relaxing" to bite one's nails.
Because of the unconscious enjoyment people get from biting nails it can be calming and comforting in a high intensity situation.
You're a perfectionist
Research presented in the Journal of Behaviour Therapy and Experimental Psychiatry discovered that people who are irritable or get angry quickly tend to be subdued by biting nails.
One research paper propsed the possibility of a link between Onychophagia - habitual biting of the nails - and family history.
One Weill Cornell Medicine professor argues that a third of nail biters have a member of their family who also bites their nails.
It's a form of Obsessive Complusive Disorder (OCD)
Although disputed in 2012 the American Psychiatry Association cited nail-biting as a form of OCD (as well as skin picking and hair pulling).
Many psychiatrists disagree with the claim, calling it an over-simplification of the disorder.
Foose said: "As an anxiety specialist, I think that was an overreach for lumping disorders."
Why you should stop
It'll cost you
Biting your nails isn't only bad for you teeth and jaw but can be the cause of high dental bills throughout your lifetime.
It can spread infection
Your hands are at the receiving end of thousands of bacteria every hour - imagine all the dirty surfaces we come into contact with each day.
Then think about putting your fingers in your mouth. The transfer of bacteria can cause infections, both in your mouth and under your nails.
It's socially unattractive
You know it looks gross. The problem for many people who bite nails is how to kick the habit. There's bitter nail polish, wearing gloves and putting tape across your nails.
Ultimately, you need to look at why you bite your nails: If it is for comfort or a calming effect the best way to stop is to replace it with something else.