Borderline personality disorder (BPD), not to be confused with Bipolar Disorder, is an illness characterised by a marked difficulty in maintaining a stable emotional state. Sufferers typically experience wide swings in their moods, their feelings about themselves and others, and in their behavior. These swings can be extreme and can last for up to days at a time.
The consequences of BPD include difficulties in maintaining stable relationships, engaging in impulsive or risky behavior, and self-harming.
Symptoms
Many of the symptoms of BPD involve emotional instability, relationship conflict, and fluctuating self-image. Common symptoms include:
- Fear of abandonment or betrayal.
- Instability in the perception of relationships. Sufferers often fluctuate between thinking that a relationship is unrealistically ideal and thinking that the relationship is extremely negative.
- Impulsive behavior.
- Self-harming behaviors and suicidal thoughts/ideation (BPD is associated with high rates of suicide — nearly all BPD patients have experienced suicidal ideation and almost 10% commit suicide by adulthood).
- Negative mood swings, including depression, anxiety, and/or irritability.
- Feelings of lethargy, emptiness, or boredom. These feelings typically occur when people are not busy or distracted, when they are not striving to connect with loved ones, or when they are preparing to go to sleep. Associated with a feeling of a lack of purpose, such as low agency and self-direction, and unfulfillment, individuals report that feelings of emptiness lead to them feeling less able to function. They might try to create feelings, or choose to inhibit intense emotions in response, using certain strategies to prevent, cope with, and alleviate the symptom of emptiness, such as engaging in impulsive behaviour, for example.
- Intense anger. These angry episodes are often irrational, and they are often followed by periods of guilt or shame.
- Episodes of “dissociation,” in which the sufferer feels as if they are disconnected from their body, or ”outside’ of reality.
- Unstable/distorted sense of self (‘identity disturbance’) sees many people with BPD abruptly and dramatically changing their self-image, with this being reflected in their appearance, goals, opinions, careers, friends, etc. They might imitate other people, developing a false sense of self and shaping their persona according to other people, out of a deep rooted fear of not being accepted.
Subtypes
Although BPD is the only official diagnosis, there are in fact four different types of BPD, albeit unofficial, which people use to describe their symptoms, as identified by one of the leading experts in the field of personality disorders and Borderline Personality Disorder, psychologist Theodore Millon* (1995).
*(Read more on this at Psychology Today).
The subtypes are as follows…
1) Discouraged/’Quiet’ type BPD
(a.k.a. ‘high-functioning’ BPD). Refers to symptoms that are displayed inwardly, instead of outwardly.
While BPD is marked by ‘under-control’ of emotional regulation, the hallmark of quiet BPD is ‘over-control.’
Being ‘over-controlled’, people with quiet BPD may be highly perfectionistic, rigid, and self-critical, constantly putting their thoughts and behaviours under harsh scrutiny. They may have a severe fear of being out of control and impose all sorts of rules on themselves to avoid this. However, their avoidance of situations that make them feel ‘out of control’, e.g., situations without order and structure, only serves to amplify their feelings of social anxiety, thus perpetuating feelings of isolation and hopelessness…
The sense of internal dysregulation and inner turmoil is the same across all types of BPD, but, because people with quiet BPD are masterful at masking their pain, they may appear cold, distant, or aloof as a result, as they avoid communicating their emotions and getting close to other people.
2) Self-destructive BPD
Sees sufferers struggling with deep-rooted feelings of low self-worth/self-hatred. They might often feel bitter and ‘deal’ with their emotions through self harm, substance abuse, suicide attempts, etc.
3) Impulsive BPD
Characterised by a tendency to act in impulsive and, often dangerous ways, usually without regard for others or the possible consequences that will arise from their actions, individuals with impulsive BPD struggle to control their sudden urges. They tend to dive into new relationships very quickly and leave them just as suddenly. There is a strong risk that people with impulsive BPD will suffer from co-occurring conditions such as substance abuse. They might be attracted to using illegal drugs or alcohol in an attempt to feel better but, in their state of impulsiveness, what starts off as ‘just a bit’ can, and often, does, end up spiraling out of control.
4) Petulant BPD
Tends to see those with the condition experiencing unpredictable mood swings in which their emotions rapidly change, going from one emotion to another, seemingly for no reason.
Torn between relying upon people and at the same time keeping their distance for fear of disappointment, individuals with petulant BPD are most likely to experience feelings which vacillate between unworthiness, and anger.
Each of the four sub-types, as referenced above, highlights a different aspect of BPD. Some people might only have symptoms from one sub-type, however, the majority of people will experience a combination of symptoms across all types, hence why ‘BPD’ is the only diagnosable term.
Despite this though, despite the fact that people cannot be diagnosed with any of the sub-types, they are not recognised diagnoses, it can still be incredibly helpful for people living with BPD to have a more specific label for what they’re experiencing , whether it is ‘official’ or not…
So, now we know what BPD is, the symptoms of BPD, and the (unofficial) sub-types, what about the causes of BPD?
Causes
It has long been considered that BPD is caused primarily by childhood abuse and trauma. Whilst it’s true that many people with BPD have experienced some form of trauma in their early years (70% according to one study, in fact), only in the past decade have researchers begun to identify underlying biological factors associated with the condition, too. Such biological factors see differences in someone with BPDs brain structure compared to someone without. For the former, their brains are, quite literally, ‘wired differently.’

The photos above show a side by side comparison of a ‘normal’ brain (on the right) vs. a ‘BPD’ brain (on the left).
The differences can be seen in the ‘heat patches’ on the two images.
Amygdala
The image of the BPD brain on the left shows a much smaller amygdala compared to the normal, healthy brain on the right. The smaller the amygdala, the more overactive it is. A vital tool for survival, the amygdala is the primitive part of the brain which regulates fear and aggression.
Because of how small the amygdala is in the brains of people with BPD (as much as 16% smaller, according to some studies), this means that, when people with Borderline Personality Disorder experience emotions, they do so more intensely than the general population, thus explaining why many people with BPD report that they ‘feel things deeply.’
Prefrontal cortex
Furthermore, differences arise in the prefrontal cortex of people with BPD VS without. The prefrontal cortex is the pinnacle of human evolution, inhibiting our primal nature. It is responsible for reason, rationality and decision-making… Because people with BPD have prefrontal cortexes which are inactive and inefficient, this majorly contributes to the reasoning behind their impulsive behaviour… With a ‘sleeping’ (I.e.. very inactive) prefrontal cortex, individuals with BPD may frequently find themselves overcome by their emotions which, in turn, might make them feel out of control.
Other differences in brain structure can be seen in the Hippocampus, and the Hypothalamic-pituary-adrenal axis (quite the mouthful)!
Hippocampus
For people with Borderline Personality Disorder, the hippocampus is in a state of continuous hyper-arousal. Uncoordinated and dysfunctional, it consistently misinterprets threats, and relays faulty messages back to the amygdala. Deciding on the correct emotional response- approach or avoidance- is therefore made extremely difficult, and can lead to people with BPD fearing intimacy, and developing an unhealthy, dysfunctional attachment style, (avoidant, anxious, or disorganised), as a direct result.
Hypothalamic-pituary-adrenal axis
The ‘Hypothalamic-pituary adrenal axis’ is primarily responsible for the body’s production* of cortisol, a natural chemical released during times of stress.
*(Production which is heightened to the extreme in people with BPD, who have abnormal levels of cortisol in their bloodstream).
With their coping skills undermined and their body overwhelmed, individuals with BPD experience intense stress in response to their cortisol levels being so high.
Now for the big old question; what causes such differences in our brains? Or rather, what causes BPD?
Whilst the heritability of Borderline Personality Disorder is estimated to be 40–60%, a massive 70% of BPD sufferers have also experienced some form of childhood trauma; often sexual, physical or emotional abuse. It therefore seems highly likely- at least, from my perspective- that BPD, and the inevitable changes in brain structure, are not solely down to genetics (although, genetics certainly do, undoubtedly, play a part, what with studies reflecting how, if you have a family history of BPD, you’re more likely to develop the condition yourself), but due to trauma as well…
To give just one example of why it is feasible that the brain is ‘injured’ by trauma, is in the chemical cortisol. Cortisol is released in response to stress; and so it goes to reason that, extreme stress, particularly stress experienced in childhood and over long periods of time, will lead to abnormal levels of production. And, with cortisol (i.e., stress) eroding parts of the amygdala and hippocampus, and prefrontal cortex away, the brain- a mirror to life- is, quite literally, ‘worn away’ by developmental trauma, stress having eroded core aspects of our lives, the most prized assets of the mind, away.
The symptoms of BPD are therefore not just mental, as the brain images show, patients with BPD are also physically unable to regulate their emotions…
Conclusion
So, it’s evident then that BPD is an extremely complex mental health condition, not just in terms of the symptoms, but also in terms of the causes. Whilst it can be difficult to stay feeling hopeful, particularly if you have been diagnosed with BPD, a condition which is still unfortunately very stigmatised, it is important to remember that there is help available. BPD isn’t ‘curable’, but it is manageable.
With the right help and support, such as psychotherapy and, if needed, medication, symptoms can be decreased.
It is possible to have BPD, and to live a happy life regardless.
There is hope for this, always.
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