Balneotherapy using naturally occurring carbonated water (more precisely, a carbon dioxide-containing spring) is at once the most traditional of therapeutic methods and also the most thoroughly studied technique in the field of applied balneotherapeutics. Sources of springs called “carbon dioxide springs” have since ancient times been used not only as spas for bathing but also for drinking. As H.D. Hentschel writes in his review of the history of carbonated water, the major direct effects had already been repeatedly observed by early spa physicians. Bode of Bad Nauheim noted a “congested, velvety, reddened skin” (1845); Piderit (1836) and Beneke (1859) described a sensation of warmth in CO2 baths and flushing of the skin in the bathed areas of the body; and in 1911 Goldscheider discussed the possibility that flushing of the skin arising from sensory stimulation by carbon dioxide may be due to vasomotion. In absorption experiments conducted by Hediger (1928), it was first demonstrated that CO2 is absorbed by passing through intact skin, although there were still many errors in the quantitative measurements taken at the time.