Invisible Perspiration

INVISIBLE PERSPIRATION, the release of water vapor and gases by the skin at average ambient temperatures. According to some authors, this is a purely physical phenomenon of the diffusion of water vapor through the epidermis without the participation of the sweat glands. This phenomenon is called hidden perspiration (reg-spiratio insensibilis) in contrast to visible perspiration (p. sensibilis), when, under the influence of increased temperature or physical exertion, the secretory activity of the sweat glands joins in. (On p. sensibilis—see Skin—Physiology.) P. i. does not manifest equally everywhere on the animal's skin territory. In particular, in humans, P. i. is most pronounced on the palms, followed in descending order by the soles, cheeks, chest, thighs, and forearms; in children, P. i. is higher than in adults. The release of water vapor by the skin depends to a significant extent on the amount of water introduced into the organism, the temperature, and the humidity of the surrounding environment. Alcohol intake reduces P. i. In addition to water vapor, gases should be attributed to hidden perspiration, the so-called skin respiration, which mainly consists of the release of CO₂ and the absorption of O₂, if one does not count the insignificant release of nitrogen and ammonia. In humans, the release of CO₂ does not exceed an average of 8–10 g per day. With an increase in the ambient temperature, as well as muscular work, gaseous perspiration is intensified, and according to the observations of Schierbeck (N. Schierbeck), for carbon dioxide it reaches 20 g at 33°, and at 38.4° it reaches 29.5 g per day.