A sauna is a heated room or small house intended to induce sweating and allow relaxation. Saunas are sometimes used for therapeutic purposes as well. Saunas have existed for hundreds of years, and there are now many different types of saunas, including smoke, heat-storage, continuous fire, and infrared.
Saunas originated in Finland, where they are an important part of local culture to this day. The most traditional form of sauna is the smoke sauna. Smoke saunas lost their popularity in the advent of newer technologies, but were revived in the 1980s. They are favored by some traditionalists, but drawbacks include difficulty of use as compared to newer types of saunas, a lengthy waiting period while the sauna heats, and large quantities of wood required for burning.
A smoke sauna contains a pile of rocks and no chimney. A fire is lit under the rocks, and when it dies out, the rocks retain some heat. Water is poured over the rocks to create steam. Though the smoke sauna is not as hot as many modern saunas, it features high humidity, which helps induce sweating.
A more modern variation of the smoke sauna is the heat-storage sauna, which includes some important innovations. The heat-storage sauna has a chimney, which reduces smoke, and a covered stone compartment, which stores heat. These saunas are hotter than traditional saunas, but also humid. The source of heat may be electric instead of from a fire.
Another type of sauna requires the constant maintenance of a fire while in use. This type, the continuous fire sauna, features a firebox, covered by stones, and a chimney. The heat of a continuous fire sauna is comparable to that of a heat-storage sauna, but it takes only about an hour to heat up. Despite this advantage, continuous fire saunas are difficult and potentially dangerous to use because the fire must be maintained continuously. Some otherwise similar saunas that use electrical heat rather than fire are safe enough to be used in the home.
One of the newest types of sauna is the infrared sauna. This type of sauna works not be heating the air, but by heating objects in the room. The infrared heat works like sunlight to penetrate the body with warmth. Some people believe that the infrared sauna offers greater health benefits over traditional saunas, and many users find that they are able to remain in an infrared sauna longer than in a traditional sauna, allowing them to sweat more.