Ageing and thermal responses during passive heat exposure: sweating and sensory aspects.

The present study investigated the causes of decreases in sweating capacities with age. The hypothesis was that the decrease in local sweat rate in older individuals was associated with deterioration in thermal cutaneous receptor responses leading to weaker signals to the thermoregulatory center (i.e. the hypothalamus). Fifteen older (>60 years), 15 middle-aged (40-50 years) and 15 young (20-30 years) men were exposed for 90 min to a 40 degrees C, 14 degrees C dew point environment. The thermal detection threshold was measured at 9 different cutaneous locations. The results showed a reduced sweat output with age, and that older and middle-aged subjects had higher core and skin temperatures than young subjects. In addition, there was a sensory thermal sensitivity decrease and a correlation between thermal sensitivity and local sweat rate in older and middle-aged subjects, but not in young subjects. The data suggest that the age-related effects on thermoregulatory mechanisms reflect local skin changes rather than central alterations.