Causes of Borderline Personality Disorder

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Borderline personality disorder (BPD) is a mental condition characterized by unstable relationships, self-image, and moods. The prevalence of BPD in the United States is 1.6%, with just under 6% of people who will have this condition at some point in their lives.

There is no consensus on what specific factors contribute to the onset or severity of the disease. However, researchers say shared aspects among people with BPD suggest that the condition is the result of a combination of genetic, biological, and environmental factors.

Depressed mature man sitting on couch
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Genetic Factors

While exact estimates vary between studies, and large-scale familial studies are still lacking, research suggests BPD aggregates in families and heritability may be as high as 46%, with the remaining variance being explained by non-shared environmental factors.

In other words, the closest family members (e.g., biological parents and twin siblings) represent a significantly high-risk group for developing BPD.

For example, researchers have found that identical twins were significantly more likely to both have BPD than either fraternal twins or non-twin siblings. The noted differences between identical and fraternal twins strengthens the claim of a genetic liability, meaning that the development of the disorder would likely have occurred even if the identical twins were separated. However, only certain traits were found to be inherited (mostly affective and interpersonal instability), and it's been suggested that others are likely due to the effect of unique environmental factors on those predisposed to BPD.

Which Genes Cause BPD?

To date, two genes are thought to contribute to BPD—DPYD and PKP4—but it is unclear how. These genes are also linked to other mental illnesses, including bipolar disorder, major depressive disorder, and schizophrenia.

Biological Factors

Biological factors, including differences in brain development, HPA axis dysregulation, and the cyclical nature of estrogen, have also been identified as potential contributing factors.

Brain Development

Researchers have found a smaller hippocampus (responsible for memory and learning) and, in certain instances, a smaller amygdala (responsible for stress modulation and the flight-or-fight response) in people with borderline personality disorder.

The hippocampus is highly susceptible to stress hormones and is easily damaged by a variety of external stimuli. Hippocampus atrophy (decrease in mass) is present in several disease states, including Alzheimer’s disease, Cushing’s disease, head injury, and PTSD.

This may explain partly why patients with BPD may have certain cognitive deficits, which could have a ripple effect on how the borderline patient perceives the world around them and can breed emotional instability (e.g., irritability and rage behaviors).

The amygdala also plays a central role in decision-making and emotional responses, including fear, anxiety, and aggression.

One study found lower functional connectivity between the amygdala and the mid-cingulate cortex (an integral part of the limbic system involved with emotion formation and processing), and this connectivity was strongly related to BPD symptomatology.

HPA Axis

The hypothalamic-pituitary-adrenal (HPA) axis refers to the body's central stress response system linking the brain and endocrine organs. It comprises the hypothalamus, the pituitary gland, and the adrenal glands. Each area of the axis acts upon the other to try and create homeostasis (balance). It is a central pathway responsible for the production and secretion of the stress hormone cortisol.

Chronic stress and childhood trauma (a risk factor of BPD) have been shown to lead to dysregulation of this axis, and this has been seen in people with BPD (i.e., individuals with BPD have shown increased urinary cortisol levels compared with control groups).


While the ovarian hormone estrogen does not cause BPD, research suggests the naturally occurring cyclical nature of estrogen across the female reproductive cycle may influence BPD symptom expression and contribute to the inconsistent, unstable characteristic of BPD in some individuals.

Environmental Factors

BPD is strongly associated with a history of childhood abuse or neglect or the disruption of family life. Estimates vary widely, but research shows BPD is associated with child abuse and neglect more than any other personality disorders with a range between 30% and 90% in BPD patients.

Forms of abuse linked to BPD include:

  • Neglect
  • Physical abuse
  • Emotional abuse
  • Sexual abuse
  • Early separation from caregivers
  • Parental insensitivity

The severity of childhood sexual abuse (by a parent or person well known to the patient or by two or more perpetrators) is significantly related to the severity of BPD and overall psychosocial impairment.

Research suggests that childhood abuse directly affects the brain. Chronic stress stimulates the HPA axis, leading to high cortisol levels, which, in turn, may affect the development of the brain in children. As such, early stresses may account for abnormalities in the size of the hippocampus and amygdala in people with BPD.

Mediating Factors

Several mediating factors are believed to either increase or decrease a vulnerable person’s susceptibility to BPD, including:

  • Executive function: The ability to problem-solve, which can mediate rejection sensitivity common in people with BPD, has been identified as a protective factor against BPD features. Strengthening solution-oriented skills may therefore be a path toward greater emotional resiliency.
  • Social interaction: Increased social interaction and inclusion mediate social relationship hypersensitivity, mentalizing (making sense of self and others), and effortful control (self-regulation of emotional reactivity and behavior) are common in people with BPD. Group work and therapy programs may therefore provide a controlled and opportune setting for people with BPD who have limited social interactions.

A Word From Verywell

New theories and a deeper understanding of the complex causes of BPD are continuously emerging and evolving. As such, there is still so much to learn about the factors contributing to one’s likelihood of developing borderline personality disorder. With new research on causes comes new avenues for effective treatments, reducing symptoms, and improving the quality of life for people with BPD.

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Michelle Pugle
Michelle Pugle, BA, MA, is an expert health writer with nearly a decade of contributing accurate and accessible health news and information to authority websites and print magazines. Her work focuses on lifestyle management, chronic illness, and mental health. Michelle is the author of Ana, Mia & Me: A Memoir From an Anorexic Teen Mind.