NAMI: National Alliance on Mental Illness | Mental Illnesses

Here is a link to the NAMI page describing BPD. It is a personality disorder (which means a longstanding pattern or way of being that began developing during childhood and has been characteristic of much of your life which includes certain symptoms identified as a particular disorder). It is generally believed that BPD is a response to some kind of ongoing trauma and/or emotional invalidation during childhood. There is a pattern of "unstable relationships" - desperately holding on to relationships sometimes, while other times pushing away. There is a book about BPD titled "I Hate You, Don't Leave Me." This relationship instability is what it refers to. Also, emotions are intense and people with BPD lack effective ways to cope with or make sense of emotions. This comes from emotional invalidation. As a child, when you keep being told that how you feel is wrong or doesn't count, you learn to hold in your feelings until you reach the point where it just explodes. It is possible that some people are predisposed to not displaying emotional cues to others which would be interpreted as distress, and then when you are upset, caretakers don't recognize it and don't respond, so you escalate, and they don't know where that came from and tell you that you didn't have a reason to blow up like that, and you aren't taught how to express emotions appropriately, and try to avoid them even more, which results in more of the same problem. Behaviors include self-destructiveness and impulsivity. You might feel empty all the time or not sure about your identity. Sometimes the connection with reality can feel shaky, and there might be dissociation.

It has been suggested that BPD is a trauma-related disorder. "Complex PTSD" is not currently included in the DSM, but is very similar to BPD. Symptoms are related to PTSD, but the traumatic event is chronic physical, sexual, or emotional abuse as opposed to one or more identifiable traumatic events that are necessarily a threat to someone's life or safety. I also consider BPD to be a dissociative disorder. Even if identities are not completely split off from each other, BPD involves fractured ego-states. There might be parts of you that have different roles and may be at odds with each other, but in BPD these parts are recognized as part of you with shared memory and experiences.