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The placebo effect in inflammatory skin reactions: the influence of verbal suggestion on itch and weal size, 2015, Darragh et al.

Discussion in 'Health News and Research unrelated to ME/CFS' started by Woolie, May 30, 2021.

  1. Woolie

    Woolie Senior Member

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    Darragh, M., Chang, J. W.-H., Booth, R. J., & Consedine, N. S. (2015). The placebo effect in inflammatory skin reactions. Journal of Psychosomatic Research, 78(5), 489–494. doi:10.1016/j.jpsychores.2015.01.011

    ResearchGate link here
    Scihub link here

    This study found that a placebo cream reduced self-reported itch relative to the same cream presented as an inert moisturiser. It did not find any direct benefits on measures of the size of the rash (weal size).

    Another example suggesting that placebo effects tend to be limited to self-reported measures, and do not extend to objective measures.

    Abstract:
     
    Last edited: May 30, 2021
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  2. Woolie

    Woolie Senior Member

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    PS I am a little uneasy about some of the analyses they did to demonstrate the self-reported benefits as well. There seem to have been a lot of covariates included in the analysis, and this is a technique that can sometimes be used retroactively, to "clean up" the results of an analysis that is non-significant, and make it significant.

    The problem isn't the "cleaning up" on the face of it, the problem is that you should not go fishing for variables that improve your results and then add in only those that do so. That can lead to a bias favouring positive outcomes. Since the study was not pre-registered, we simply cannot know what practices they employed to decide on what covariates to include.

    It's worth noting that this was a healthy sample who had rashes induced by histamine administration on the skin site. It's also worth noting that the self-reported measures were immediate measures, so may be different in character from reports that are based on retrospective evaluation of symptoms over a longer period.

    Edited to add: The self-report measures were immediate, but even they showed a marked drop off over the course of a few minutes, suggesting that this type of "placebo" effect, if reliable, is extremely short-lived indeed. Can't see much use for it clinically, unless its applied during a surgical procedure or the like.
     
    Last edited: May 30, 2021
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  3. Sly Saint

    Sly Saint Senior Member (Voting Rights)

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  4. rvallee

    rvallee Senior Member (Voting Rights)

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    Yes, moisturizing a dry itch will... moisturize it, and thus itch less. Duh.

    I actually had this experience, thinking I had some type of fungus on my skin and occasionally used antifungal cream. Moisturizing cream works just as well, because it reduces the itchiness by the sacred moisturizing power of water. It's just an itch with flaky dry skin.

    The whole "think horses not zebras" thing is really arbitrary, ain't it? Because this is Occam's razor's obvious explanation. But sure, there's also Rube Goldberg's blunt mace of bluntness' explanation, the least likely explanation there is, one that requires introducing all sorts of bizarre cosmic weirdness.

    Or just moisturize it, the essence of water and beauty. It works on dry skin. Like I saw many times what most dermatology is in a nutshell, when in doubt wet dry skin and dry wet skin, apply steroids as needed.
     
  5. Woolie

    Woolie Senior Member

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    That's as may be, but the measure of interest is how the self-reports were affected by the way the cream was presented to the participants - whether as having a direct treatment effect of not.

    (I have eczema, and moisturiser does f-all. Makes my skin actually hotter and more itchy for the first half hour. Its gotta be the corticosteroid cream or no dice. I think doctors see the dry skin look that accompanies eczema, and imagine that somehow the dryness caused the eczema - hence the obsession with moisturiser - but its the other way around. The dryness goes away when the eczema is treated).
     
  6. Snow Leopard

    Snow Leopard Senior Member (Voting Rights)

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    This is a classic and ubiquitous non-sequitur found in medical science. Self-reported symptoms is not the same as experienced symptoms but is almost always assumed to be the same thing.
     
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