Itching for Affective Touch: Studying the Influence of Temperature and Velocity on Itch Reduction

Abstract

Itch is an understudied and poorly understood symptom of various dermatological conditions for which treatment is still sparse. Research has shown that affective touch (AT), or touch delivered at 3 cm/s, exerts inhibitory effects on the sensation of itch. This relationship is seemingly sustained by low threshold unmyelinated mechano-afferents (C-tactile or CT) in the human hairy skin. The processing of temperature and velocity of touch is moderated by CT-fiber activation and is in turn hypothesized to mediate the degree of inhibition on itch. In the present study, we investigated whether theoretically optimal stimulation of CT-fibers (3 cm/s touch at 32°C) significantly increases their inhibitory effect on itch. A within-subjects design (N = 17) consisting of 2 x (touch: 3 cm/s, 18 cm/s) 2 x (temperature: 18°C, 32°C) x 7 (timepoints: VAS baseline and measurements) conditions was employed to compare the effect of velocity and temperature of touch on itch modulation. Itch was induced electrically, and touch was administered affectively (3 cm/s) or non-affectively (18 cm/s) at a temperature of 18°C or 32°C, respectively. Participants rated the development of itch seven times during six minutes and the pleasantness of touch once every condition, on a visual analogue scale (VAS). The results indicated that AT was significantly more effective in decreasing itch than the non-AT condition (p = 0.034). Notably, the relationship between itch and touch was not mediated by subjective pleasantness. However, the hypothesis that touch delivered at 32°C would be significantly better at decreasing itch could not be confirmed (p = 0.549). In sum, the present study highlights the relieving effect that slow caress exercises on itch and offers new insights into the relationship between itch and touch.