The placebo effect in inflammatory skin reactions The influence of verbal suggestion on itch and weal size Margot Darragh, Joshua W-H. Chang, Roger J. Booth, Nathan S. Consedine ⁎ The University of Auckland, New Zealand abstract article info Article history: Received 26 August 2014 Received in revised form 19 January 2015 Accepted 21 January 2015 Keywords: Placebo response Placebo effect Inflammatory skin reactions Suggestion Purpose: To investigate suggestion-induced placebo effects in inflammatory skin reactions. Methods: A 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. Par- ticipants were randomly allocated to undergo either the control or the treatment session first. Results: The placebo manipulation successfully reduced self-reported itch from the control to the placebo treat- ment 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 administra- tion, but this disappeared at the three and five minute measures. Conclusion: Findings suggest that explicit verbal suggestion can reduce the experience of itch. In addition to con- scious awareness, a concrete representation of the suggested changes gained from prior experience to the stim- ulus may be an important component of placebo effects on inflammatory skin reactions. © 2015 Elsevier Inc. All rights reserved. Introduction The relative importance of psychological factors in skin conditions such as urticaria continues to be debated [1], but there is empirical evi- dence to suggest that they can influence the experience of itch [2,3] and contribute to idiopathic conditions such as chronic spontaneous urticar- ia [4]. The way an individual thinks and feels appears to impact the sta- tus of the skin; however, whether this ‘mind–body’ relationship can be harnessed to ameliorate the symptoms of skin conditions is less clear. The placebo effect is an intriguing phenomenon in which individuals experience benefit from pharmacologically inert treatments [5]. Expec- tation, an established mechanism of some placebo effects, is when the patient or participant's expectation of improvement generates real psy- chobiological changes [6]. Explicit suggestion of benefit is often used to induce expectations, such as providing verbal instructions that a treat- ment cream will reduce the experience of pain [7]. Placebo-induced ex- pectations are thought to modulate internal homeostatic processes by activating top-down, neurobiological pathways [6,8]. Thus, placebo research has been described as investigations into the ‘impact of expec- tations on brain–mind–body interactions’ [9 p. 1922]. While psychological factors are known to influence the immune sys- tem [10], there is a paucity of evidence demonstrating that placebo ex- pectancy can exert changes on immune parameters [11]. One possible reason for this is that certain placebo protocols may be more appropri- ate for the manipulation of certain outcomes. For example, those out- comes of which we are consciously aware (such as pain or motor function) can be influenced by suggestion, unlike those that are not con- sciously detectable, such as hormone release [12]. Therefore, in order for a suggestive placebo protocol to be effective, a conscious awareness of the suggested changes may be needed [13]. Given the nature of the im- mune system, this type of awareness is often not possible; however, in- flammatory skin reactions can be seen and felt [14], and may be an appropriate target for suggestive placebo protocols. Only a few studies have attempted to influence inflammatory skin reactions by way of suggestive placebo protocols. One study aimed to reduce histamine induced skin reactions with verbal suggestion and the application of topical ‘anti-histamine’ (placebo) cream [15]. While the manipulation was not successful, the suggestion did not explicitly suggest a smaller weal size or a reduction in perceived itch, but instead a ‘dampened’ response to the histamine. Another study demonstrated a suggestion-induced increase in itchiness, but the suggestion of decreased itchiness was not successful [16]. A recent study demonstrated that while verbal suggestion alone did not modulate itch, placebo effects Journal of Psychosomatic Research 78 (2015) 489–494 ⁎ Corresponding author at: University of Auckland, Department of Psychological Medicine, Faculty of Medical and Health Sciences, Private Bag 92019, Auckland Mail Centre, Auckland 1142, New Zealand. Tel.: +64 9 923 5976. E-mail addresses: m.darragh@auckland.ac.nz (M. Darragh), wcha657@aucklanduni.ac.nz (J.W.-H. Chang), rj.booth@auckland.ac.nz (R.J. Booth), n.consedine@auckland.ac.nz (N.S. Consedine). http://dx.doi.org/10.1016/j.jpsychores.2015.01.011 0022-3999/© 2015 Elsevier Inc. All rights reserved. Contents lists available at ScienceDirect Journal of Psychosomatic Research