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How does DID/OSDD develop?

The theory of structural dissociation assumes that no one is born with an ‘integrated’ personality. Every person is born with different ‘parts’ of themselves called ego states that are more tied directly to needs than complex emotions. Over time, these ego states will naturally integrate into one seamless and coherent personality, generally by the age of about 7-9.

However, repeated childhood trauma can disrupt this process of integration. Ego states will be unable to merge and integrate due to conflicting needs, trauma responses, trauma memories, or learned actions due to trauma. A coherent sense of self cannot seamlessly form when the child is safe in one moment and in fight/flight/freeze/fawn the next, putting their body in survival mode.

Depending on the severity or degree to which the ego states cannot integrate, this can result in various disorders. It can result in PTSD, c-PTSD, BPD, or – if it gets to the point where amnesiac barriers get built between the ego states to protect them from the knowledge of what’s happening to one another – it can result in DID.

Layman’s Definition

Have you ever seen a little kid feel ‘melancholy’ or ‘bittersweet’? Probably not! No, they’re usually happy, sad, hungry, tired, angry – the extremes. That’s because – according to the theory of structural dissociation – everything starts out separately. Happy and sad can talk to each other, but they aren’t “there” simultaneously. It’s one and then the other.

Around 7-9 years old, those parts start naturally melding together so that kids can feel those complex emotions, and so they aren’t so all-or-nothing anymore – it’s a natural part of development. Trauma kind of messes with that.


Let’s say a child lives with her mom, and her mom has a boyfriend who stays with them on the weekends. On the weekends, that boyfriend sexually abuses that child. And she knows her mom knows. This goes on for months or even years, and she mentally can’t get through the week knowing what she will have to deal with on the weekend without breaking down. She can’t talk to her mom and feels that she can’t talk to anyone else – she’s a kid and doesn’t know what to do. But her brain is still young, and her ego states (happy, sad, mad, scared) are still separate.

This is when she develops structural amnesia so that she “forgets” the weekend. And the part of her that experiences the weekend might forget the week. They both live their own lives. Now, one girl can get through the week and be a happy child without knowledge of the trauma happening every weekend. Her brain has sectioned a part away from her knowledge and awareness because that’s a scared part, an angry part, or a strong part, and she doesn’t have communication with that part anymore. Now that child has DID. That child has developed that coping mechanism for further trauma and may split again in the future and can develop more and more sectioned-off parts or “alters” to deal with other traumatic things for the rest of her life because her brain learned that this works. This keeps her ‘safe’… at least mentally.

End Trigger Warning

Core Theory

Core theory is the theory that there is one ‘original’ or ‘main’ personality. There are other alters who split off from that core. If there were to be a final fusion of a system – viewed through core theory – they would fuse back to be that core once more, with more memories and understanding. Perhaps with a few shifted traits from the alters who fused, but the core personality is generally seen as dominant in the sense that it will be withstanding throughout the system’s life.

Core theory is used less frequently these days, with structural dissociation being the leading theory in the field. That being said, some systems identify with a core. Some people may struggle with validating those alters if they believe in the theory of structural dissociation. Firstly, identity should be respected, and if that’s how their system identifies, just respect them – it doesn’t matter your views outside. However, there’s also a reason some systems could identify more with a core while they still were formed through structural dissociation.

If a system went through its trauma after most of its ego states had already merged, it may have had an almost fully formed identity with only one or two ego states left to merge when it formed DID/OSDD. If that’s the case, they may have formed more of what might feel like a ‘core’ – rather than a system that had all their ego states separated when they formed DID and, therefore, started out much more fractured. This is, of course, just a theory, but for systems out there struggling with feeling like they have a core but believing in the theory of structural dissociation, this could be an explanation.

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