Borderline personality disorder: signs, how it differs from mood swings, causes and treatment

CareOps editorial team · October 28, 2026 · 11 min read

Mental wellness information and service guidance published by CareOps.

A reply comes a little late and you're sure they're about to leave you. Someone who felt like the best person in the world yesterday feels unbearable today, and in between, your own sense of who you are keeps blurring. When this keeps happening, you may come across the term “borderline personality disorder.” Here is what it refers to, its signs, how it differs from mood swings and bipolar disorder, and how it is treated and improves.

What is borderline personality disorder? #

The U.S. National Institute of Mental Health (NIMH) describes borderline personality disorder as a mental illness that affects how a person feels about themselves and others and makes everyday life hard to manage. At its root there is often difficulty regulating emotions, which leads to impulsive behavior, a shifting sense of self and troubled relationships. It is usually diagnosed in late adolescence or early adulthood.

Because of the words “personality disorder,” it is easy to mistake it for meaning someone has a bad character. It doesn't mean that. It is closer to a state in which emotions rise far more strongly and quickly than for others and don't settle easily, so holding onto relationships and a steady sense of self becomes unusually exhausting. And there are treatments with a growing body of evidence.

Signs of borderline personality disorder #

These are the signs NIMH lists. It isn't a way to sort people; it shows which difficulties tend to overlap, and not everyone experiences all of them. How intense, frequent and long-lasting they are also varies from person to person.

• Fear of abandonment: to avoid being left, real or perceived, you may jump into relationships quickly or cut them off first.
• Intense, unstable relationships: swinging between extremes, from adoring someone to finding them unbearable.
• Sensitivity to rejection: small rejections hurt deeply, and you feel cut off or alone.
• An unstable self-image: who you are, what you like and what you value keep changing.
• Strong mood shifts lasting hours to days: emotions rise and fall sharply and don't settle easily.
• Chronic emptiness: a hollow feeling that lingers for a long time.
• Intense anger: anger that is out of proportion or hard to control.
• Dissociation: feeling detached from yourself, as if watching from outside, or disconnected from your surroundings.
• Impulsive behavior: spending sprees, binge eating, reckless driving or substance use done in the moment and regretted later.
• Thoughts of self-harm or suicide: in unbearable emotional pain, these thoughts or behaviors can recur.

Having one or two of these doesn't mean someone has borderline personality disorder. Fear of being left is common in anxious attachment, and emptiness is common when you are feeling empty. It is something a professional looks at when many of these signs appear together over a long time, across many relationships and situations, and seriously disrupt life.

How is it different from mood swings and bipolar disorder? #

All three can look alike because moods go up and down, so they are often confused. A review comparing the two disorders (Paris & Black, 2015) explains that mood shifts in borderline personality disorder are brief and happen in response to stress between people, whereas in bipolar disorder mood changes are sustained. NIMH also notes that borderline symptoms occur without the clearly elevated mood of mania or hypomania. Below is a rough guide; a diagnosis is made in a clinical visit.

The two can occur together, and depression, anxiety, post-traumatic stress and eating problems often come along too (NIMH). If your mood changes many times a day, see when mood swings are severe. If elevated and low periods last for days at a time, see bipolar disorder symptoms.

What causes borderline personality disorder? #

The exact cause is not yet known. NIMH considers genetic, physical, environmental and social factors as working together to raise the risk.

• Family history: having a close relative, such as a parent or sibling, with the condition may raise the risk.
• Brain structure and function: differences have been reported in areas that manage impulses and emotions. It is still unclear whether these are a cause or a result of living with the condition.
• Early experiences and relationships: many people report hardships such as abuse, neglect or abandonment in childhood, or long exposure to unstable relationships in which their feelings were not accepted.

Still, having these experiences doesn't mean it will develop, and it can develop without them. Rather than tracing the cause to one person or one event, knowing which moments set off big emotional swings now is more useful for moving forward.

Is there a borderline personality disorder test? #

There are many short checklists online, but borderline personality disorder isn't determined by a quick test. According to NIMH, a licensed mental health professional makes the diagnosis after a thorough conversation about symptoms and personal and family history, and may rule out physical causes. Because it overlaps so much with depression and bipolar disorder, it is a diagnosis that takes time. That is why CareOps does not offer a borderline personality disorder test.

What you can do is look at how you usually handle emotions. The CareOps emotion regulation check (ERQ) is not a borderline personality disorder test; it is a 10-item check on how much you use reappraisal (seeing a situation differently) and suppression (not showing feelings). For the broader struggle with emotions that rise fast and strong, see emotional dysregulation.

Treatment for borderline personality disorder #

NIMH names psychotherapy as the primary treatment for borderline personality disorder. The best-known approach, dialectical behavior therapy (DBT), was developed specifically for it. Along with mindfulness of present-moment emotions, it teaches skills to handle intense feelings, reduce self-destructive behavior and improve relationships. Cognitive behavioral therapy (CBT), which looks at the links between thoughts and behavior, is also used.

The evidence has grown. A Cochrane review of 75 randomized controlled trials with 4,507 participants (Storebø et al., 2020) found that psychotherapy tailored to borderline personality disorder reduced symptom severity compared with usual care, and the most studied approaches were DBT (a third of all trials) and mentalization-based treatment (MBT). Another meta-analysis of 33 trials (Cristea et al., 2017) also found DBT and psychodynamic approaches more effective than control conditions. Both note that effects are modest and the quality of evidence varies, so rather than assuming one therapy suits everyone, what matters is finding a fitting treatment and sticking with it.

NIMH explains that the benefit of medication is unclear, so it is not a first-line treatment, though it may be added to psychotherapy for specific symptoms or co-occurring conditions such as mood swings or depression. Whether medication is needed is decided with your doctor. You can read more about DBT's four skill areas in emotional dysregulation and about calming emotions day to day in how to regulate emotions.

Can borderline personality disorder get better? #

Borderline personality disorder was long seen as lifelong, but long-term studies have shown a different picture. In a study that followed 175 people who sought treatment for 10 years (Gunderson et al., 2011), 85% no longer met the diagnostic criteria (remission), and 12% met them again later. A 16-year follow-up of 290 people who had been hospitalized (Zanarini et al., 2012) found that 78–99% reached symptomatic remission.

The same studies also showed that rebuilding work and relationships takes longer than symptom relief. In the 16-year study, 40–60% reached recovery, meaning symptomatic remission along with good social and work functioning. So treatment continues beyond reducing symptoms, toward rebuilding daily life and relationships too.

If a family member or partner has borderline personality disorder #

When someone close has big emotional swings, the people around them can wear out too. Telling someone who hasn't been diagnosed “you have borderline personality disorder” can make the relationship harder, so leave diagnosis to a professional. NIMH suggests these ways to help.

• Learn about the condition to understand what your loved one is going through. Change can be hard and frightening, but things can improve with time.
• Offer validation, understanding and patience rather than judgment.
• Encourage them to stay in treatment, and look into family therapy together.
• Take any talk of self-harm or suicide seriously, and help them reach a mental health professional or a crisis line (109 in Korea).
• Get counseling for yourself as well, ideally with a different therapist than theirs.

Caring for them and protecting yourself can go together. If you keep falling apart within the relationship, it's okay to think about how much distance you need. If conflict in the family has gone on for a long time, see family conflict.

If you need a place to put shifting feelings into words #

Putting the days your emotions swung hard into words helps you start to see what touched off those feelings. CareOps Maeumi is an AI counseling app that runs sessions with approaches such as cognitive behavioral therapy (CBT) and acceptance and commitment therapy (ACT). It helps you look at the thoughts and actions in the moments emotions surged, and remembers past sessions so you can pick up the thread next time. Get the app

This guide shares mental wellness information. If you are in immediate danger, contact emergency services where you are. Support and contact information.