Robert C. Darling

Relationship between evaporation rate of sweat and mean sweating rate

The rate of evaporation of sweat under a step change of ambient temperature (30-45 degrees C) was compared with the mean sweating rate (MSR) computed from five simultaneous resistance hygrometric measurements. Empirical equations derived for the conditions studied enabled a direct conversion from hygrometric measurements into real evaporative sweat losses and skin wetness for all phases of sweat evaporation. From five chosen skin areas, forehead, forearm, chest, thigh, and calf, it was found that none of these sites gave a local sweating response close to the MSR. In the subjects with a forehead sweating rate within +/- 39% of the MSR, at least four hygrometric sensors were needed to predict the rate of sweat evaporation. For subjects with higher forehead sweating rates, at least five sensors were necessary to calculate the evaporative sweat loss.