Increased skin wetness independently augments cool‐seeking behaviour during passive heat stress

Abstract

Skin wetness occurring secondary to the build-up of sweat on the skin provokes thermal discomfort, the precursor to engaging in cool-seeking behaviour. Associative evidence indicates that skin wetness stimulates cool-seeking behaviour to a greater extent than increases in core and mean skin temperatures. The independent contribution of skin wetness to cool-seeking behaviour during heat stress has never been established. We demonstrate that skin wetness augments cool-seeking behaviour during passive heat stress independently of differential increases in skin temperature and core temperature. We also identify that perceptions of skin wetness were not elevated despite increases in actual skin wetness. These data support the proposition that afferent signalling from skin wetness enhances the desire to engage in cool-seeking behaviour during passive heat stress. This study tested the hypothesis that elevations in skin wetness augments cool-seeking behaviour during passive heat stress. Twelve subjects (6 females, age: 24±2 y) donned a water-perfused suit circulating 34°C water and completed two trials resting supine in a 28.5±0.4°C environment. The trials involved a 20min baseline period (26±3% relative humidity (RH)), 60min while ambient humidity was maintained at 26±3% RH (LOW) or increased to 67±5% RH (HIGH), followed by 60min passive heat stress (HS) where the water temperature in the suit was incrementally increased to 50°C. Subjects were able to seek cooling when their neck was thermally uncomfortable by pressing a button. Each button press initiated 30s of -20°C fluid perfusing through a custom-made device secured against the skin on the dorsal neck. Mean skin (Tskin ) and core (Tcore ) temperatures, mean skin wetness (Wskin ) and neck device temperature (Tdevice ) were measured continuously. Cool-seeking behaviour was determined from total time receiving cooling (TTcool ) and cumulative button presses. Tskin and Tcore increased during HS (P<0.01) but were not different between conditions (P≥0.11). Wskin was elevated in HIGH vs. LOW during HS (60min: by +0.06±0.07 a.u., P≤0.04). Tdevice was lower in HIGH vs. LOW at 40-50min of HS (P≤0.01). TTcool was greater for HIGH (330±172s) vs. LOW (225±167s, P<0.01), while the number of cumulative button presses was greater from 40-60min in HS for HIGH vs. LOW (P≤0.04). Increased skin wetness amplifies the engagement in cool-seeking behaviour during passive heat stress.