Alain-Raymond van Abbe, a former health industry and cosmetics promoter, estimates the world's pathological nail biters number 600 million or more. He saw that onychophagy was so widespread that he has opened a business devoted to a cure.

"In four weeks, nail biting can be over - and over forever," he says.

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.

Van Abbe, whose field is marketing rather than medicine, describes himself as a problem solver.

His treatment relies 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.

"After four weeks, the impulse disturbance is so frustrated that it is controlled. You don't have any problem any more," he said.

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.