Borderline personality disorder (BPD) is a mental illness characterized by instability in moods, behavior, and relationships. It is caused by a combination of genetic and environmental factors such as childhood trauma. People with BPD may experience extreme mood swings, impulsivity, feelings of emptiness, fear of abandonment, and unstable self-image. Treatment involves medication to reduce symptoms like anxiety and depression as well as psychotherapy approaches like dialectical behavior therapy which teach skills for managing emotions and improving relationships.