About 30ml carbon dioxide permeates the skin per minute for every 1m2 of body surface area, in a spa of at least 90% gas concentration, 90% humidity and 30C temperature.
Vessels in the skin dilate; the capillary and plexus sub papillary circulation intensifies; arteriolae dilate; preformed collaterals (side branches of blood vessels) open up, and the speed of blood flow increases.
While these changes can be seen in microscope examinations, the increased blood flow to the tissues will also be seen and felt by the patient. Skin temperature increases and secretions from sweat glands intensify.
As well as proven vasodilatory effects, CO2 also creates a physiological response called the Bohr Effect.
This effect allows skin, muscles and organs to receive more oxygen. The greater the level of carbon dioxide haemoglobin more readily acquires and releases oxygen molecules into the fluid that surrounds it.