Now a Dutch businessman, Alain-Raymond van Abbe, is offering what he calls sure-fire cure.
Four weeks flat you can get rid of that habit for ever, he claims. He is relying on a tooth guard molded to fit either the upper or lower teeth. Barely visible, the 'preventer' makes it impossible to bite, but can be removed for eating.
Abbe, a former health industry and cosmetics promoter, estimates the world's pathological nail biters number 600 million or more. He saw that onychophagy (as the habit is called) was so widespread that he has opened a business devoted to a cure.
'After four weeks, the impulse disturbance is so frustrated that it is controlled. You don't have any problem any more,' he said.
Studies show around 45 percent of adolescents nibble their nails. That drops to about 20 percent as young adults learn to cope with their anxieties or become too embarrassed by their self-inflicted deformity.
In public, compulsive biters typically keep their hands out of sight as much as they can, buried in their pockets or behind their backs. They often feel depressed and shamed, and avoid social contacts. Van Abbe says his clients suffer so much from the stigma that none would volunteer to be interviewed or photographed.
He calculates Holland alone has 2 million chronic sufferers, enough to keep his enterprise busy and profitable. He charges up to $670 for a course of treatment.
After developing his solution over two years and working with about 150 pilot customers, Van Abbe refitted a gabled brick house in Venlo, near the German border, with reclining leather manicurists' chairs where cosmeticians can begin reviving damaged finger and toe nails.
Yes, some of his clients habitually bite their toe nails, including one man in his 40s, Van Abbe said. 'If you start young, you stay flexible.'
Nail biting is one of a category of obsessive-compulsive disorders known as Body-Focused Repetitive Behaviors that is gaining more scientific attention. Others include hair pulling, skin picking or incessantly biting the inside of the cheek.
Lawrence S. Micheletti, an assistant professor of psychiatry at the University of Texas Medical Branch, says most research on nail biting focuses on the psychological stress and on the therapies that treat the source of the problem.
But there also is a chicken-and-egg factor, because the ugly result of self-mutilation heightens anxiety. 'If you cure the symptom, you reduce the stress, and the person is a happier person,' Micheletti said in a telephone interview.
Micheletti, who works with many adolescents in stress management, says nail biting is one of the most common symptoms he sees among his patients.
He said Van Abbe appeared to have developed 'a plausible approach' since, in clinical terms, the treatment involves both cognitive and behavioral aspects. But he wonders about Van Abbe's business model.
'I never thought of opening a clinic just for nail biters,' he said. 'I wouldn't want to rely just on nail biters to make my living.'