A sauna is a small room designed to be heated to very high temperatures, with well-controlled humidity. Saunas are used both for recreational and therapeutic purposes, with most people using to relax, as well as for their health benefits. Most are built of aromatic wood, which releases pleasing aromas as they heat.
There are two main types of saunas: dry and wet. Which type you prefer is just a matter of taste. Wet saunas are sometimes called steam rooms, and are kept at lower temperatures than their dry counterparts — usually between 100 to 115°F (37 to 46°C) to prevent the superheated water from scalding the skin on contact. Dry saunas may be kept at much higher temperatures of up to 250 Fahrenheit (121 Celsius), by keeping the ambient moisture down to nearly zero.
Many saunas, even those using electric heaters, have some form of hot fragrant rocks which may be splashed with water to release both a short burst of steam, (temporarily creating the impression of a higher temperature), and a pleasing aroma. Some wood-burning ones choose their fuels very carefully to help stimulate the participants through scent.
Many cultures have independently created their own form of hot room. The Finnish sauna, which is by far the most popular globally, originated as a hole in the ground with a fire in the middle and an insulating roof. Many First Nations people of North America use a traditional sweat lodge. These may be as simple as a hole dug in the ground, or as complex as an entire wooden long-house style structure. In most First Nations' saunas there is no internal fire; instead, stones are heated in a fire outside of the building and transported into the sweat lodge. Even many desert peoples have their own variants of the sauna, usually with full humidity and lower temperatures.
Saunas are thought by many to be best used alternating hot and cold. To this end, spending enough time in the room to become hot, and then leaving it to cool back down, before repeating, is an ideal way to use the sauna to its full potential. Many people enjoy jumping into very cold water between sessions. This shock is thought by some to be good for the immune system, though others hold it can be detrimental to one's health. Those with high blood pressure should be especially careful of this immediate transition from hot to cold, as it spikes blood pressure for brief periods.
Alcohol should never be used in tandem with a sauna, but should be particularly avoided if one has a low blood pressure. Spending time in intense heat causes surface capillaries to dilate, lowering blood pressure even further. When mixed with alcohol this can cause lightheadedness or fainting.