Sauna

A sauna (/ˈsɔːnə/ or /ˈsaʊnə/; Finnish pronunciation: [ˈsɑunɑ]), or sudatory, is a small room or building designed as a place to experience dry or wet heat sessions, or an establishment with one or more of these facilities. The steam and high heat make the bathers perspire. Infrared therapy is often referred to as a type of sauna, but according to the Finnish sauna organizations, infrared is not a sauna.

Modern saunas
Under many circumstances, temperatures approaching and exceeding 100 °C (212 °F) would be completely intolerable and possibly fatal if exposed to long periods of time. Saunas overcome this problem by controlling the humidity. The hottest Finnish saunas have relatively low humidity levels in which steam is generated by pouring water on the hot stones. This allows air temperatures that could boil water to be tolerated and even enjoyed for longer periods of time. Steam baths, such as the Turkish bath, where the humidity approaches 100%, will be set to a much lower temperature of around 40 °C (104 °F) to compensate. The "wet heat" would cause scalding if the temperature were set much higher.

In a typical Finnish sauna, the temperature of the air, the room and the benches is above the dew point even when water is thrown on the hot stones and vaporized. Thus, they remain dry. In contrast, the sauna bathers are at about 38 °C (100 °F), which is below the dew point, so that water is condensed on the bathers' skin. This process releases heat and makes the steam feel hot.

Finer control over the temperature experienced can be achieved by choosing a higher level bench for those wishing a hotter experience or a lower level bench for a more moderate temperature. A good sauna has a relatively small temperature gradient between the various seating levels. Doors need to be kept closed and used quickly to maintain the temperature inside.

Some North American, Western European, Japanese, Russian, and South African public sport centres and gyms include sauna facilities. They may also be present at public and private swimming pools. As an additional facility, a sauna may have one or more jacuzzis. In some spa centers, there are the so-called special "snow rooms," also known as a cold sauna or cryotherapy. Operating at a temperature of −110 °C (−166 °F), the user is in the sauna for a period of only about 3 minutes.

Use
A steam sauna can take 30 minutes to heat up when first started. Some users prefer taking a warm shower beforehand to speed up perspiration in the sauna. When in the sauna users often sit on a towel for hygiene and put a towel over the head if the face feels too hot but the body feels comfortable. In Russia, a felt "banya hat" may be worn to shield the head from the heat; this allows the wearer to increase the heat on the rest of the body. Most adjustment of temperature in a sauna comes from,

• amount of water thrown on the heater, this increases humidity, so that sauna bathers perspire more copiously.
• length of stay in the sauna
• positioning when in the sauna

Heating caused by direct radiation will be greatest closest to the stove. Heating from the air will be lower on the lower benches as the hot air rises. Provided the sauna is not crowded, lying on a bench is considered preferable as it gives more even temperature over the body. Heating caused by fresh steam can be very different in different parts of the sauna. As the steam rises directly upwards it will spread across the roof and travel out towards the corners, where it will then be forced downwards. Consequently, the heat of fresh steam may sometimes be felt most strongly in the furthest corners of the sauna. Users increase duration and the heat gradually over time as they adapt to sauna. When pouring water onto the heater, it will cool down the heater, but carry more heat into the air via advection, making the sauna warmer.

Perspiration is a sign of autonomic responses trying to cool the body. Users are advised to leave the sauna if the heat becomes unbearable, or if they feel faint or ill. Some saunas have a thermostat to adjust temperature, but management and other users expect to be consulted before changes are made. The sauna heater and rocks are very hot—one must stay well clear to avoid injury, particularly when water is poured on the sauna rocks, which creates an immediate blast of steam. Combustibles on or near the heater have been known to result in fire. Contact lenses dry out in the heat. Jewellery or anything metallic, including glasses, will get hot in the sauna and can cause discomfort or burning.

Temperature on different parts of the body can be adjusted by shielding from the steam radiator with a towel. Shielding the face with a towel has been found to reduce the perception of heat. It may be advisable to put an additional towel or special cap on the hair to avoid dryness. Few people can sit directly in front of the heater without feeling too hot from radiant heat, but their overall body temperature may be insufficient. As the person’s body is often the coolest object in a sauna room, steam will condense into water on the skin; this can be confused with perspiration.

Cooling down is a part of the sauna cycle and is as important as the heating. Among users it is considered good practice to take a few moments after exiting a sauna before entering a cold plunge, and to enter a plunge pool by stepping into it gradually, rather than immediately immersing fully. In summer, a session is often started with a cold shower. Therapeutic sauna has been shown to aid adaptation, reduce stress hormones, lower blood pressure and improve cardiovascular conditions.
en.wikipedia.org