The response of the sweat glands of the newborn baby to thermal stimuli and to intradermal acetylcholine.

1. Measurements of evaporative sweat loss were made on fifty-six premature and full-term babies 1-67 days after birth with an infra-red analyser and a ventilated capsule placed on the thigh. Measurements were also made of total evaporative water loss while in a closed metabolic chamber and of the regional distribution of sweating with starch-iodine paper.2. No sweating to thermal stimuli could be detected in infants of less than 210 days post-conceptual age, even when rectal temperature rose as high as 37.8 degrees C. In older infants sweat was detected first on the forehead and temple, later on the chest, and usually by 240-260 days post-conceptual age on the legs (term approximately 268 days). Generalized sweating on the limbs appeared at an earlier post-conceptual age in the more prematurely born infants.3. The response of sweat glands on the thigh to an intradermal injection of 2 mug acetylcholine (ACh) was tested. No sweat response was detected in infants under 225 days post-conceptual age, while all infants born within 2 weeks of term responded. The response was often augmented after 2-5 tests at 5-10 min intervals; all the eight infants born within 2 weeks of term who were examined twice in the first 2 weeks of life showed a greater response on the second occasion.4. An average of 414 active sweat glands/cm(2) were detected on the thigh in eight babies 7-10 days old born within 2 weeks of term. This was 6(1/2) times the number found in adults. The mean peak sweat rate to chemical stimulation was however only 2.4 nl./gland.min, which was 3 times lower than the maximum rate recorded in adults.5. In five infants with congenital defects of the brain and complete absence of temperature control there was no sweat response to thermal or direct chemical stimulation of the glands.6. Functional maturation appears to depend on intact central innervation and is marginally hastened by post-natal factors. Immaturity of the sweat glands can account for the lack of any response to thermal stimuli in premature babies, but not for the modest thermal response obtained in babies at term.