Traditional steam/hot rock saunas raise the temperature of the air in the sauna cabin in order to warm the body. Far infrared (FIR) saunas use the safe warming properties of the sun's far infrared spectrum to warm the body rather than the air within the cabin. This process is called conversion. FIR warms only the object and does not raise the temperature of the surrounding air. To understand how infrared heat works, picture yourself outdoors on a summer day with the sun beaming overhead. Your body feels warm from the sun and you become hot. Then a cloud passes overhead, blocking out the sun. The temperature outside has not changed, but you feel cooler in the shade. Your body was being heated by the sun's far infrared rays. Infrared heaters warm the body in the same manner as natural sunlight.
All life requires FIR heat from the sun. FIR heat is not ultraviolet radiation but a narrow band of energy within the 5 to 15 micron level. This type of energy travels 40 - 45 mm deep into the body. The sun is the primary source of radiant energy but not all of this energy is beneficial. Sunlight also contains harmful ultraviolet rays which are not present in the far infrared sauna. FIR heat provides the healthy benefits of natural sunlight without any of the dangerous effects of ultraviolet rays.
The healthcare industry has used infrared heat lamps as a source of FIR heat for many years (Eg to warm prematurely born babies) however the heating lamps were cumbersome, extremely hot and difficult to maintain at a constant temperature. The recent development of ceramic and carbon fibre infrared heaters created a new and convenient source of FIR heat.
If we don't spend enough time outdoors then we may not receive enough infrared in our bodies. While far infrared penetrates and heats our body and causes us to sweat, the composition of chemicals found in the sweat is quite different from that produced by a steam bath, traditional steam/hot rock sauna, or exercise. The sweat of people using a far infrared sauna will not only contain water but will also contain cholesterol, fat-soluble toxins, heavy metals (such as mercury, aluminum, and arsenic), nicotine, sulfuric acid, ammonia, and other undesirable elements. Normal sweat produced by other methods, including exercise, is mostly water and sodium chloride (salt).
The regular use of an infrared sauna has a cumulative effect on the body, meaning that using it on a regular basis magnifies its benefits.