The placebo effect in inflammatory skin reactions: The influence of verbal suggestion on itch and weal size

Abstract

PurposeTo investigate suggestion-induced placebo effects in inflammatory skin reactions. MethodsA healthy sample of volunteers (N=48) attended two laboratory sessions. In each, a local short term inflammatory skin reaction was induced with histamine. Participants were told that one session was a control session and the other was a treatment session in which an antihistamine cream would be applied to the arm to reduce the size of the weal and the experience of itch. Inert aqueous cream was applied in both sessions. Participants were randomly allocated to undergo either the control or the treatment session first. ResultsThe placebo manipulation successfully reduced self-reported itch from the control to the placebo treatment session, but no placebo effect was demonstrated in weal size. Order effects were observed such that only those who underwent control procedures first had a smaller weal in the placebo treatment session as compared to the control session. The same order effect was seen for reported itch at one minute post histamine administration, but this disappeared at the three and five minute measures. ConclusionFindings suggest that explicit verbal suggestion can reduce the experience of itch. In addition to conscious awareness, a concrete representation of the suggested changes gained from prior experience to the stimulus may be an important component of placebo effects on inflammatory skin reactions.