Response of term babies to a warm environment.

The response of healthy term babies to warm environments was assessed by placing them naked in incubators and increasing the air temperature in steps until either sweating occurred or the rectal temperature reached 37.9 degrees C. The rate of evaporation of water from the skin was measured by a method based on the estimation of vapour pressure gradient. When a 50% increase in the rate occurred at a given site, sweating was judged to have begun. 39 studies were made on 30 babies, aged from 4 hours to 11 days. As babies approached the point of sweating, spontaneous activity usually ceased, the skin reddened, and a sunbathing posture was adopted. Sweating was found on 35 occasions. It was most pronounced and often was found initially on the forehead but it was also detected on the trunk and limbs. No thermal sweating was noted on the palms or soles. Sweating generally began when the incubator air temperature exceeded 34 degrees C and the rectal temperature exceeded 37.1 degrees C, but there was wide individual variation. Older and more mature babies tended to sweat at lower air temperatures.