A medical sauna is a sauna that heats its occupants with heaters that emit far infrared radiation. Unlike conventional saunas, which use heated steam, an infrared sauna does not heat the air. An infrared sauna is usually a wooden box containing several infrared heaters, although an infrared sauna could be open air and still heat the users in the same manner. In essence, the sauna box creates the atmosphere of the sauna while the heaters create the actual heating effect.

Infrared radiation heats the skin directly without warming the air. In infrared saunas, a heater produces this radiant energy, which is similar to the heat from the sun. Most of these heaters draw on technology developed in 1965 by Dr. Tadashi Ishikawa, a member of the Research and Development Department of Fuji Medical.

Infrared sauna promoters state that infrared radiant heat is safe and beneficial, claiming that the heat penetrates more than 1.5 inches into the body. They claim this heals and stimulates tissues, and that it is effective therapy for arthritis and tissue injuries. Promoters claim that using infrared saunas allows one to achieve health benefits similar to those from a conventional steam sauna or sweat.