The factors involved in the evocation and maintenance of body focused repetitive behaviours (BFRBs), such as nail biting and nose picking are little understood. Research to date has focused on maintaining factors. One hypothesis is that they are evoked by arousal or stress. Other studies have demonstrated that the presence of other people reduces the frequency of BFRBs. To test this, drivers were observed during morning and evening peak hours. The results showed that BFRBs were more frequent when drivers were alone and less frequent when drivers were conveying a passenger. They were also more frequent in the morning than in the evening. The discussion considers the role of social presence and stress as motivational operations or discriminative stimuli
