While the cause of personality disorders is complex and not fully understood, the predominant risk factor is genetics. Personality disorders tend to run in families. The risk is especially increased for those who have a first-degree relative with a personality disorder. This is particularly true for antisocial personality disorder, which is marked by criminal activity, disregard for the law, and impulsive acting out that often results in disciplinary or legal problems.
Some research suggests that environmental factors may play a role as well. For instance, many people who meet diagnostic criteria for borderline personality disorder, or BPD, report having experienced traumatic life events, such as abuse or abandonment during childhood. Many people with BPD also describe their childhoods as highly dismissive and invalidating. However, some people with BPD have no history of trauma, and most people who do have a history of traumatic life events do not go on to develop BPD.