The main difference between these two is fundamentally how they produce heat. Infrared saunas use light (usually red) in the infrared spectrum of different wavelengths to excite the air molecules, penetrate body tissue, and produce heat. Steam saunas, as the name suggests, produce heat in the air by adding steam to it. Either an electric heater or fire warms sauna rocks, and water is carefully ladled over them to produce steam and warm the sauna.