Osmotic Pressure of Human Sweat

¹ From the Department of Physiology and Health Service Research Unit, University of Illinois, Urbana, Illinois

The osmotic pressure of forearm sweat and of blood serum has been measured in a single individual in 48 sweating experiments involving varied rates of sweating and states of body hydration. The osmotic pressure of the sweat averaged 68.4 (range 47–101) mOs/l. Osmotic pressure of sweat varied directly with the rate of sweating when the body was adequately hydrated. In dehydration the osmotic pressure of the sweat was elevated while the rate of sweating remained low. The sweat remained hypotonic to the blood serum. The osmotic work necessary to effect dilution of the sweat was calculated to be not more than 10 gram calories per minute for the whole body surface. A scheme for the formation of sweat is suggested.