Seasonal variation of sweating responses under identical heat stress.

The seasonal variation of sweating responses under identical heat stress was investigated to make clear the seasonal acclimatization in daily human life on the experiments. The heat stress of 33 degrees C air temperature, 50% relative humidity laid in the experiments was chosen as a usual daytime condition in summer in metropolitan cities such as Tokyo and Osaka. Five subjects were exposed under the identical heat stress in the climate chamber every two months through the year. Results were discussed on the mean values for five subjects. Although the relation of skin temperature to daily mean air temperature showed a variation of high in summer and low in winter before the heat stress, it rose and showed almost constant value during the heat stress. The seasonal variation of tympanic temperature appeared a little before the heat stress, but disappeared during the heat stress. The seasonal variation of sweating responses was evident, that was high in summer and low in winter. The concluding remarks are as follows: 1) It could be considered that there is a seasonal acclimatization on the threshold temperature for sweat onset. 2) The seasonal acclimatization on sweating is supposed to be caused by the seasonal acclimatization of the threshold temperature. 3) The seasonal acclimatization on sweating could be comprehended in four stages corresponding closely to the daily mean air temperature (Ta). The 1st stage is December-April when Ta < 15 degrees C, the 2nd stage is April-August when 15 degrees C < Ta < 25 degrees C, the 3rd stage is the term centering on August when Ta > 25 degrees C and the 4th stage is August-December when 15 degrees C < Ta < 25 degrees C.