The heat source for infrared saunas is Far-Infrared Radiant (FIR) heat. It is simply a form of energy that is directly transmitted onto objects because of its specific wavelength. It has nothing to do with ultraviolet light which is known to cause sunburn and damage skin.
Conventional saunas transfer heat by circulating hot air - warming your body from your head down whereas infrared heat rays warm your body directly. This allows an in-depth heat at a more pleasant temperature of 100-150°F providing more health benefits and a highly enjoyable and comfortable environment.