Borderline personality disorder (BPD) is a mental health condition characterized by pervasive patterns of instability in emotions, self-image, interpersonal relationships, and behaviour. People with BPD often experience intense mood swings, fear of abandonment, difficulties managing anger, impulsive behaviours, and chronic feelings of emptiness. Self-harm and suicidal behaviours or threats may occur, sometimes as a means of coping with overwhelming emotions or to regulate relationships. Cognition can also be affected: there may be transient, stress-related paranoid ideas or dissociation. Symptoms typically begin in adolescence or early adulthood and can vary in severity over time.

Core features

• Emotional dysregulation: rapid, intense shifts in mood and difficulty returning to baseline after upset.

• Interpersonal instability: idealising and devaluing others, intense fears of real or imagined abandonment, and volatile relationships.

• Identity disturbance: unstable or unclear sense of self, shifting goals, values, and aspirations.

• Impulsivity: behaviours that are potentially self-damaging (e.g., substance use, binge eating, reckless driving, impulsive spending).

• Self-harm and suicidal behaviour: non-suicidal self-injury and suicide attempts are relatively common.

• Dissociation or transient paranoia: stress-related episodes of feeling detached or suspicious.

Causes and risk factors

• Biological vulnerabilities: genetic factors, temperamental sensitivity to emotion, and neurobiological differences in brain systems that regulate emotion and impulse control.

• Developmental and environmental factors: early attachment disruptions, childhood trauma (including abuse and neglect), and invalidating environments that consistently dismiss or punish emotional expression.

• Interactions between biology and environment: sensitivity plus adverse early experiences increases risk.

BPD is treatable. Evidence-based approaches combine psychotherapy as the foundation, with adjunctive use of medication and psychosocial supports as needed. Treatment aims include reduction in self-harm and suicidality, improved emotion regulation, more stable relationships and identity, and enhancement of functioning and quality of life.

Psychotherapies with strongest evidence

• Dialectical Behaviour Therapy (DBT): a structured, skills-based therapy developed specifically for BPD. DBT targets emotion regulation, distress tolerance, interpersonal effectiveness, and mindfulness. It typically includes individual therapy, group skills training, phone coaching, and a consultation team for therapists. DBT reduces self-harm and suicidal behaviour and improves emotional control.

With appropriate treatment, many people experience significant improvement in symptoms and quality of life