Experimental framework and methods for the assessment of skin wetness sensing in humans

International audienceThe study of the human ability to both detect the presence and estimate the amount of wetness on the skin has grown in scientific interest over the last century, due the implication of wetness in comfort and skin health. In 1900, Bentley demonstrated that skin wetness is detected based on touch and temperature stimuli combining to produce sensations of liquidity, and that wetness perception increases with cold touch. It has since been demonstrated that, in the absence of a skin hygroreceptor (i.e., wetness receptor), the biophysical effects of moisture on the skin-conductive heat transfer and mechanical interaction-excite specific cutaneous mechanoreceptors and thermoreceptors. The resulting afferent signals are centrally integrated to generate our perception of skin wetness. As well as providing a theoretical foundation for the understanding of this aspect of somatosensation, these insights have helped develop a methodological framework for the study of human skin wetness sensing, which relies on assessing the independent and interactive effects of thermo-tactile stimulation of the skin in the presence of a liquid. This chapter will provide an overview of the experimental framework and methods available to evaluate the biophysical and psychophysical responses to controlled dry and wet stimuli applied to skin, and the resulting wetness perception. We will use example scenarios of skin-moisture interactions (e.g., arising from contact with a wet surface or from sweat production), to critically evaluate the methods, noting their accuracy, reliability and efficiency, and discuss their inherent limitations and commonly encountered difficulties. It is hoped that these considerations will guide and further develop research of this relatively littleinvestigated, yet fundamental, aspect of somatosensation