Sweat from gland to skin surface – production, transport and skin absorption

By combining galvanic skin conductance (GSC), stratum corneum hydration (HYD) and regional surface sweat rate (RSR) measurements at the arm, thigh, back and chest, we closely monitored the passage of sweat from gland to skin surface. Through a varied exercise-rest protocol, sweating was increased slowly and decreased in 16 male and female human participants (25.3 {plus minus} 4.7 yrs, 174.6 {plus minus} 10.1 cm, 71.3 {plus minus} 12.0 kg, 53.0 {plus minus} 6.8 ml∙kg∙min-1). ∆GSC and HYD increased prior to RSR, indicating pre-secretory sweat gland activity and skin hydration. ∆GSC and HYD typically increased concomitantly during rest in a warm environment (30.1 {plus minus} 1.0{degree sign}C, 30.0 {plus minus} 4.7% RH) and only at the arm did ∆GSC increase prior to an increase in HYD. HYD increased prior to RSR, before sweat was visible on the skin, but not to full saturation, contradicting earlier hypotheses. Maximal skin hydration did occur, as demonstrated by a plateau in all regions. Post exercise rest resulted in a rapid decrease in HYD and RSR but a delayed decline in ∆GSC. Evidence for reabsorption of surface sweat into the skin following a decline in sweating, as hypothesized in the literature, was not found. This suggests that skin surface sweat, after sweating is decreased, may not diffuse back into the dermis, but is only evaporated. These data, showing distinctly different responses for the three measured variables, provide useful information about the fate of sweat from gland to surface that is relevant across numerous research fields (e.g. thermoregulation, dermatology, ergonomics and material design).