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This chapter uses the phrase nail biting rather than onychophagia because nail biting is more easily understood. Although most nail biters bite only their fingernails, some people bite their toenails as well or overclip their toenails. Occasionally, people may bite their nails as part of a behavioral disorder occasioned by intense pain. Nail biting can be reliably and simply measured by using calipers. For older teenagers and adults, the data from Malone and Massler's study indicate that fewer girls and women than boys and men bite their nails. Studies of obsessive-compulsive spectrum disorders have often revealed quite high levels of nail biting, among other habits. Only one trial of pharmacological agents has been described, in which clomipramine and desimipramine were compared in a double-blind, randomized study. A number of interventions have been proposed, but none has shown clear superiority in adequately designed trials.