The role of decreasing contact temperatures in the perception of wetness on the skin

Previous studies have indicated that the perception of wetness on the skin results from the integration of the somatosensory sub-modalities of touch and temperature [1]. However, how these inputs interact to evoke this synthetic perception is still unclear [2]

Body mapping of thermal sensitivity to skin wetness across the torso

Humidity receptors have never been identified on human skin and the ability to perceive skin wetness has been suggested to rely on the sensory inputs arising from thermal cold afferents. However, limited data are available on how thermal afferents and their regional distribution influence the perception of wetness. PURPOSE: Given the regional variability in thermal sensitivity across the torso, here we examined whether regional differences in the sensitivity to wetness exist

Regional differences in the cutaneous thermal sensitivity to wetness across the torso

Humans are not provided with humidity receptors and the ability to perceive skin wetness seems to rely on the sensory inputs arising from thermal cold afferents. Given the regional variability in thermal sensitivity across the torso, we examined whether regional differences in the sensitivity to wetness exist. Sixteen male participants were tested at rest. Twelve regions of the torso were stimulated with a dry or wet thermal probe (25cm²) set at a temperature of 15°C below the local skin temperature, which was measured pre and post stimulation. Thermal and wetness sensations were recorded using likert scales. As a result of the same relative cold stimuli, the skin cooling response varied by location and regional differences were found in thermal and wetness sensations. The lateral chest showed the greater drop in local skin temperature. Colder sensations were reported on the lateral abdomen and lower back. Greater wetness was reported on the lower back. No differences were perceived between wet and dry stimuli, the dry ones perceived as wet as the wet ones. The regional variability in wetness sensitivity showed a pattern similar to the thermal sensitivity to cold. We conclude that, as thermal cold afferents seem to have a critical role in driving the perception of wetness, based on the regional variability in thermal sensitivity, humans present regional differences in the cutaneous sensitivity to wetness across the torso

Upper and lower body sensitivity to cold at rest and during exercise

Upper and lower body sensitivity to cold at rest and during exercis

Individual ability to discriminate between wetness and dryness during short contacts with a warm surface

The interaction between thermal and touch sensing seems to be largely acknowledged as the principal responsible of the perception of skin wetness [1]. However, it is still unclear which sensory input is essential or sufficient to generate this perception [2]

Thermal and tactile interactions in the perception of local skin wetness at rest and during exercise in thermo-neutral and warm environments

The central integration of thermal (i.e. cold) and mechanical (i.e. pressure) sensory afferents is suggested as to underpin the perception of skin wetness. However, the role of temperature and mechanical inputs, and their interaction, is still unclear. Also, it is unknown whether this intra-sensory interaction changes according to the activity performed or the environmental conditions. Hence, we investigated the role of peripheral cold afferents, and their interaction with tactile afferents, in the perception of local skin wetness during rest and exercise in thermo-neutral and warm environments. Six cold-dry stimuli, characterised by decreasing temperatures [i.e. -4, -8 and -15°C below the local skin temperature (Tsk)] and by different mechanical pressures [i.e. low pressure (LP): 7 kPa; high pressure (HP): 10 kPa], were applied on the back of 8 female participants (age 21 ± 1 years), while they were resting or cycling in 22 or 33°C ambient temperature. Mean and local Tsk, thermal and wetness perceptions were recorded during the tests. Cold-dry stimuli produced drops in Tsk with cooling rates in a range of 0.06 to 0.4°C/s. Colder stimuli resulted in increasing coldness and in stimuli being significantly more often perceived as wet, particularly when producing skin cooling rates of 0.18°C/s and 0.35°C/s. However, when stimuli were applied with HP, local wetness perceptions were significantly attenuated. Wetter perceptions were recorded during exercise in the warm environment. We conclude that thermal inputs from peripheral cutaneous afferents are critical in characterizing the perception of local skin wetness. However, the role of these inputs might be modulated by an intra-sensory interaction with the tactile afferents. These findings indicate that human sensory integration is remarkably multimodal

A comparison of galvanic skin conductance and skin wettedness as indicators of thermal discomfort during moderate and high metabolic rates

The relationship between local thermal comfort, local skin wettedness (w) and local galvanic skin conductance (GSC) in four body segments during two different exercise intensities was compared in 10 males. In a balanced order, participants walked at 35% VO for 45min (WALK) (29.0±1.9°C, 29.8±3.6% RH, no wind) in one test and in a separate test ran at 70% VO for 45min (RUN) (26.2±2.1°C, 31.1±7.0% RH, no wind). During both tests, participants wore a loose fitting 100% polyester long sleeve top and trouser ensemble with a low resistance to heat and vapour transfer (total thermal resistance of 0.154mKW and total water vapour resistance of 35.9mPaW). w, change from baseline in GSC (δGSC) and local thermal comfort were recorded every 5min. The results suggest that both w and δGSC are strong predictors of thermal comfort during the WALK when sweat production is low and thermal discomfort minimal (r>0.78 and r>0.71, respectively). Interestingly, during the RUN w plateaued at ~0.6 to 0.8 due to the high sweat production, whilst δGSC gradually increased throughout the experiment. δGSC had a similar relationship with thermal comfort to w during the RUN (r>0.95 and r>0.94, respectively). Despite the strength of these relationships, the ability of w to predict local thermal comfort accurately dramatically reduces in the exponential part of the curve. In a situation of uncompensated heat stress such as high metabolic rate in hot climate, where sweat production is high, δGSC shows to be a better predictor of local thermal comfort than w. The w data shows regional differences in the threshold which triggers local discomfort during the WALK than RUN; lower values are found for upper arms (0.22±0.03 and 0.28 ±0.22) and upper legs (0.22±0.11 and 0.22±0.10), higher values for upper back (0.30±0.12 and 0.36 ±0.10) and chest (0.27±0.10 and 0.39 ±0.32), respectively. However, no regional differences in the threshold of discomfort are found in the {increment}GSC data. Instead, the data suggests that the degree of discomfort experienced appears to be related to the amount of sweat within and around the skin (as indirectly measured by δGSC) at each body site. © 2013 Elsevier Ltd

Sex differences in thermal strain induced by a typical hiking scenario in a cool environment

Most research investigating hill walking has focused on the mechanisms of accidental hypothermia with protocols involving males exposed to prolonged wet and windy environments [1]. No attention has been paid to discomfort associated with the different phases of recreational hiking in non-adverse conditions. The present study was designed to evaluate overall and local thermal strain during a typical hiking scenario and to highlight potential differences between males and females. This knowledge can be of practical importance for improved clothing requirement

Different physiological responses but similar thermal perceptions for males with various body fatness during cold air exposure

There is no consensus regarding the potential effect of body fatness on subjective responses to cold at rest [1,2]. Most studies have examined overall sensation and comfort with no attention to regional values or the influence of exercise on thermal perception. The present study aimed at exploring overall and regional perceptual responses of males, varying in body fat content (¿) in association with their physiological responses, specifically regional skin temperatures (Tsk)