Can itch-related visual stimuli alone provoke a scratch response in healthy individuals?

Abstract

The sensation of itch and the scratch response elicited by application of histamine are enhanced by itch-related visual cues in people with existing skin conditions and, to a lesser extent, in healthy controls. We tested whether visual cues alone could generate feelings of itch and provoke a scratch response in healthy volunteers. A secondary aim was to assess whether the content of some pictures evoked these sensations more effectively. Thirty participants viewed static images that were either itch-related (e.g. ants, fleas or skin conditions) or neutral (e.g. butterflies or healthy skin). These were further separated by picture type into 'skin contact' (e.g. ants crawling on the hand or a butterfly on a finger), 'skin response' (e.g. scratching an insect bite or washing the hands) or 'context only' (e.g. viewing midges or birds flying). The sensation of itch was successfully generated using itch-related pictures, with higher self-reports of itch in answer to the questions 'How itchy do you feel?' and 'How itchy do you think the person in the picture feels?', compared with viewing neutral pictures (P<0·001), and these measures correlated (P≤ 0·003). Participants also scratched themselves more when viewing itch-related pictures than when viewing neutral ones (P<0·001). The interaction with picture type was significant, with more scratching behaviour recorded when viewing pictures depicting others scratching (P=0·01). This study demonstrates the impact of visual cues in eliciting sensations of itch and provoking a scratch response, and may provide behavioural evidence linking contagious itch to the mirror neuron system.