Triggering itch in laboratory studies using histamine or audio‐visual materials

Abstract

Summary Itch is a major symptom of many skin diseases, and in some scientific studies, researchers want to deliberately trigger an itch on volunteers’ skin. There are different methods to induce itch in laboratory settings. One possibility is to transfer an itch inducing substance produced by the body, called histamine, into the skin by use of a light current. This method is called histamine‐iontophoresis and requires ‘direct skin manipulation’. A different, ‘non‐skin manipulating’ method is providing the volunteers with itch‐related audio‐visual material (for example, slides or videos of crawling insects). From other studies it is well‐known that the experience of itch also depends on the person's attention. With this study researchers from Germany aimed to find out whether itch induced (triggered) by audio‐visual material is comparable to itch induced by histamine‐iontophoresis in two situations: not focusing on the skin before itch induction (study 1a) and focusing on the skin before itch induction (study 1b). In study 1a, all 80 subjects rested for 10 minutes. Then 40 of them were shown the itch inducing video, while in the other 40 histamine was applied. Study 1b was the same as 1a, except that instead of resting for 10 minutes, all 80 subjects watched a non‐itch inducing video on the skin before receiving either histamine itch‐induction (40 people) or watching itch‐related audio‐visual material (40 people). Itch was measured by asking the participants how intense their maximum itch was, and how intense the itch was immediately after it was induced. The researchers found that the maximum itch induced by audio‐visual material was comparable to the maximum itch induced by histamine, but only when subjects watched a non‐itch inducing video on the skin before itch induction (study 1b). However, histamine‐induced itch was actually more intense when volunteers did not focus on the skin before itch induction (study 1a). This suggests that channelling the attention of the volunteers before itch induction is important when researchers would like to use itch‐related stimuli (such as audio‐visual materials) in their studies as an alternative to histamine‐iontophoresis. This is a summary of the study: Itch induction by audiovisual stimuli and histamine iontophoresis: a randomized, controlled, noninferiority study.