I am going to be purchasing a sauna before fall. I have been researching them for the last couple of months. The following is from Sunlight Sauna's website. I hope this helps answer your question.
Far Infrared Sauna s increase the body's core temperature. This helps the body rid itself of harmful toxins through a deeper sweat. Conventional hot rock/steam heater saunas heat the air with steam, which can often be unbearably hot and you will only sweat on the surface. Steam also makes the air difficult to breath. A Far Infrared Sauna uses dry far infrared heat that is well ventilated and extremely comfortable and relaxing.