Causes - Borderline personality disorder

Borderline personality disorder (BPD) is caused by a combination of factors.

Your genes

There is evidence that BPD can run in families. This means that genes you inherit may make you more likely to develop it.

Problem with brain chemicals

It's thought that many people with BPD have something wrong with the neurotransmitters in their brain, particularly serotonin.

Neurotransmitters are "messenger chemicals" used by your brain to transmit signals between brain cells. Altered levels of serotonin have been linked to depression, aggression and difficulty controlling destructive urges.

Brain development

Difficulties with 3 parts of the brain may cause symptoms of BPD.

These are the:

• amygdala - plays an important role in regulating emotions
• hippocampus - helps regulate behaviour and self-control
• orbitofrontal cortex - helps planning and decision making

Research shows that in many people with BPD these parts of the brain were smaller or had unusual levels of activity.

The development of these parts of the brain is affected by your experiences during childhood.

These parts of your brain are also thought to have a role in regulating your mood. They may cause some of the difficulties people with BPD have in close relationships.

Difficult or traumatic life events

There are some difficult or traumatic experiences that may be common in people with BPD.

These include:

• being a victim of emotional, physical or sexual abuse
• feeling fear or distress long-term as a child
• being neglected by 1 or both parents
• growing up with a family member who had a mental health difficulty - for example, a problem with substance use

Your relationship with your family has a strong influence on how you come to see the world. It influences what you believe about other people.

Feelings of fear, anger or distress from childhood that have not been resolved can lead to certain ways of thinking about yourself and other people.

For example:

• idealising others (thinking they are better than they are)
• expecting others to be a parent to you
• expecting other people to bully you
• behaving as if other people are adults and you're not