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reader comments: nocebo
1 March 2011
I found one of the studies you quote does not seem to be adequately referenced in the sources: Japanese researchers tested 57 high school boys for their sensitivity to allergens. The boys filled out questionnaires about past experiences with plants, including lacquer trees, which can cause itchy rashes much as poison oak and poison ivy do. Boys who reported having severe reactions to the poisonous trees were blindfolded. Researchers brushed one arm with leaves from a lacquer tree but told the boys they were chestnut tree leaves. The scientists stroked the other arm with chestnut tree leaves but said the foliage came from a lacquer tree. Within minutes the arm the boys believed to have been exposed to the poisonous tree began to react, turning red and developing a bumpy, itchy rash. In most cases the arm that had contact with the actual poison did not react." (Gardiner Morse, "The nocebo effect," Hippocrates, November 1999, Hippocrates.com)
I found this astonishing, and decided to follow the references. You cite the Hipprocrates article. The journal is now defunct, but I found the article here: It references "a review" of "scattered studies" in Medline by Dr Robert Hahn who is still at the CDC. With the assistance of the fine StackExchange skeptics: (I am not sure if that is available to you until it gets out of beta) I learnt that the review from Dr Hahn is probably this one: Hahn RA. The nocebo phenomenon: concept, evidence, and implications for public health. Prev Med. 1997 Sep-Oct;26(5 Pt 1):607-11. I don't have access to read that, but someone who did explained that "Unfortunately, the study about the rash is not mentioned in that review. It only mentions other studies, e.g. "A double-blind study of symptom provocation to determine food sensitivity."
I do not doubt that nocebos have odd powers, but this one astonished me with the idea that the brain could secrete chemicals that will produce a rash at a particular part of the skin on an arm. I wonder if any rashes were caused by scratching instead (which is a mechanism I could understand.) Now that I find (at least to my meagre abilities) that the original study was not referenced by the sources, I find it far less compelling. I hope this information is useful to you.
Last updated 01-Mar-2011