Most everyone plays mindlessly with their hair from time to time. But for some people it becomes such an uncontrollable compulsion that they end up with bald patches or eyebrows plucked bare.

If it's any comfort, animals too suffer from "grooming compulsions."

Though the behavior is documented in the Bible and ancient medical texts, treatment for hair-pulling has not been studied much. But now a University of Minnesota researcher might have found an answer in a common, over-the-counter nutritional supplement that costs about $15 for 100 pills.

Better yet, his breakthrough could hold promise for a whole range of common obsessive behaviors, from nail-biting to hand-washing.

Dr. Jon Grant, a psychiatrist who specializes in addictive and compulsive behaviors, found that an antioxidant called N-acetylcysteine (NAC) helped about half of the hair-pullers in his study. Some engaged the behavior less often, and some quit altogether.

It's not a cure-all, Grant said, because it didn't work in the other half of his subjects. Still, the study, published Monday in the Archives of General Psychiatry, is important because it shows for the first time that reducing a certain chemical in the brain also eases an uncontrollable behavioral obsession.

Extreme hair-pulling is relatively uncommon compared to other grooming compulsions such as nail-biting, he said, but it occurs in all cultures and in animals.

"Dogs lick themselves to the point of hair loss," he said. "Parrots pull out all their feathers."

Some studies have shown that anywhere from 1 to 4 percent of people engage in hair-pulling at some point in their lives, more often in women than men. Like most obsessive behaviors, it's probably genetic. But the people who suffer from it often suffer in silence and shame, Grant said.