Yes, this behavior could indicate a compulsion or it could be a sign of another disorder called Trichotillomania. I would probably not think of this pattern as "normal cosmetic behavior," in part because she loses track of time while engaging in it. However, sometimes people play with their hair (or even pull hair) as an anxious habit or during times of stress. Obsessive-compulsive disorder is a type of anxiety disorder. In this case, hair pulling could be a compulsive action since it is repetitive behavior, especially if she "can't stop" (i.e., feels compelled to perform). However, there are several other criteria necessary to diagnose such behavior as obsessive-compulsive disorder (OCD). For instance, the person must feel driven to perform the behavior according to quite rigid rules and/or in response to an obsession. Simply put, an obsession is a persistent, intrusive, inappropriate, and anxiety-provoking thought that's more than just excessive worry about real-life problems and that the person has trouble suppressing. In addition, for OCD, the person must be attempting to reduce or prevent the obsessive distress by performing the compulsive behavior. So, your girlfriend's repetitive hair pulling that seems "driven" to you might even be what many would call a compulsive habit but fall short of qualifying as OCD. Trichotillomania is a pattern of recurrent hair pulling that results in noticeable hair loss. Typically, this pattern would also include an increasing tension or sense of urgency prior to the hair pulling, or when a person is resisting the urge, and an experience of relief, gratification, and/or pleasure when pulling the hair out. For diagnosis of trichotillomania, the person must also experience significant distress or difficulty in social, work, or other areas of functioning. Bottom line: If this behavior causes emotional distress, results in physical/medical problems (e.g., infections, rash, etc.), or significantly interferes with your girlfriend's every day functioning in any way, I'd be concerned and want to encourage her to talk with a mental health counselor or medical provider about the problem. Otherwise, this may be one of those "quirks" you have to accept or tolerate if you stay in the relationship.