Personality Disorders: What Are They, Symptoms, and Treatment What Are Personality Disorders? Personality disorders are long-standing and ingrained behaviors that affect a person's thoughts, feelings, and behaviors. These behaviors can have a negative impact on a person's daily life and relationships. Personality Disorders Causes The causes of personality disorders are not fully understood, but genetics, environmental factors, and changes in brain structures are thought to play a role. Personality Disorders Types Personality disorders are classified into 10 different categories in the DSM-5 (Diagnostic and Statistical Manual of Mental Disorders). These categories are created according to the fundamental characteristics of personality disorders. Cluster A Personality Disorders: These disorders lead to inconsistencies and abnormalities in a person's thoughts and behaviors. Paranoid, schizoid, and schizotypal personality disorders are included in this category. Cluster B Per...