nail biting - 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. According to Freudian theory, nail biting a symptom of oral fixation. The clinical name for nail biting is chronic onychophagia. Nail biting may result in transportation of bacteria that are buried under the surface of the nail that are hard to clean and easy to get in your mouth. Likewise, broken skin on the cuticle may be susceptible to microbial and viral infections. These pathogens can be spread between digits via saliva. A long-time habit of nailbiting may have detrimental effects on the substantia adamantinea of the front teeth, promoting caries in these areas. 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.