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It is sometimes claimed that the multiple personalities of a person with dissociative identity disorder may not only display different character, behaviour, and movement types, but even show different functionings of the body. Quoting,

One example is a boy who endures allergic reactions when drinking orange juice including symptoms such as hives and water filled blisters which subside immediately when he switches to a different personality.

Another mention of (probably) the same case is here. So to be concrete: Is this particular story correct?

In general: Have there been verified cases of split personalities with significant differences in body function, such as a different immune system, different hormone levels or different physical strength?

While my first link provides some references to publications on this topic, I am uncertain as to whether they represent the scientific consensus, in particular in light of the controversy on split personalities mentioned at this related (and still unanswered) question.

This question was inspired by the movie Split, where this is a major theme.

Fizz
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Saibot
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    If nobody on this site is able to answer if multiple personalities even exist, how would someone be able to answer the title question? – paradisi Jul 01 '17 at 00:45
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    A related question: [Did a nocebo study find that rashes could swap hands?](https://skeptics.stackexchange.com/questions/127) – paradisi Jul 01 '17 at 00:46
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    @sumelic: Mainly by providing a negative answer to this question without arguing against the existence of multiple personalities as such. But even a positive answer to this question may not presuppose a positive answer to the other one: different personalities may display different physical traits *even if* DID is merely therapy-induced. – Saibot Jul 01 '17 at 01:19
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    Closely related: https://skeptics.stackexchange.com/questions/6766/can-mental-state-affect-eye-color – Oddthinking Jul 01 '17 at 05:13
  • So, on the whim of my brain, all of the evil bacteria in my body disappear without a trace, then reappear in the entirety of their previous strength at another whim of my brain? I find that hard to believe. – John Dvorak Jul 01 '17 at 14:34
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    @sumelic re. [Multiple personalities: Do they exist?](https://skeptics.stackexchange.com/questions/6783/) I think that question from 2011 is unanswered because it's too vaguely defined, it'd probably be closed if it was asked today. There's no doubt that dissociative disorders exist, or that some show what appear to be separate personalities and memories; the controversy is around what causes it and whether these people truly *can't* have awareness, control or access to memories, or whether there's an element of role play or social influence *shaping* the "personalities"... – user56reinstatemonica8 Jul 02 '17 at 20:42
  • ...I don't think this question would require "Hollywood-style" multiple personalities, I imagine any dissociative disorder linked with changes in something like an allergy would fit the bill (e.g. if someone loses or gains an allergy only during a dissociaitive fugue). It seems potentially plausible, for example PTSD is known to sometimes change skin, immune, and inflammation related conditions (e.g. [point 4 in this abstract](http://www.sciencedirect.com/science/article/pii/S0738081X17300196)) – user56reinstatemonica8 Jul 02 '17 at 20:47
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    @JanDvorak: There is such a thing as [somatic symptom disorder](https://en.wikipedia.org/wiki/Somatic_symptom_disorder). I wouldn't expect someone to switch between HIV positive / negative, but I could readily picture, for example, differing allergic symptoms. – DevSolar Jul 03 '17 at 12:05
  • Different physical strength also seems possible. Most of the training benefits you get when you start strength training is muscle coordination. The muscles aren't that much stronger, but they work better together. It's possible that different personalities can coordinate muscles better. –  Jul 03 '17 at 16:31
  • @Toby: Your statement about muscle coordination sounds really interesting, do you have a reference for that? – Saibot Jul 03 '17 at 19:37
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    @JanDvorak most symptoms of transient illnesses are not the bacteria/viruses at work, but the body's response to the contagion. Overproduction of mucus or histamines, elevated body temperature, coughing and sneezing are all common examples. Brain (and gut) chemistry is responsible for these changes, as well as being the root of personality, so a link between personality and symptoms is certainly possible. – Asher Jul 05 '17 at 21:54
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    The journal article "Dissociative identity disorder and ambivalence" *Philosophical Explorations*, volume 19, page 223, https://doi.org/10.1080/13869795.2016.1199728 says "there is some evidence that they may even have different allergies", but I don't have easy access to the full text. – DavePhD Sep 30 '19 at 11:58

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According to The Phenomenon of Dissociation, Australian Institute of Professional Counsellors :

The phrase “dissociative identity disorder” replaced “multiple personality disorder” because the new name emphasises the disruption of a person’s identity that characterises the disorder, while the term dissociation draws attention to the actual mental process taking place. When under the control of one identity, (i.e. when those aspects of self are in the conscious foreground), the person is usually unable to remember some of the events that occurred while other personalities were in control. The different identities, referred to as alters, can develop so independently of one another that they exhibit differences in speech, mannerisms, attitudes, thoughts, and gender orientation. The alters may differ in “physical” properties such as allergies, right-or-left handedness, or even the need for eye glass prescriptions. The differences are distinct and can often be quite striking to the observer (Haddock, 2001).

where "Haddock, 2001" is The dissociative identity disorder resource book [sic sourcebook].

DavePhD
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    Thank you! The second to last sentence in that quote looks promising. However, I don't yet see how that book is relevant: google's search comes up empty for either of "allergy", "allergies", "handed" and "handedness". I currently don't have access to the full text, so I may be missing something. – Saibot Oct 02 '19 at 18:47