The steam and high heat make the bathers perspire. A thermometer in a sauna is typically used to measure temperature; a hygrometer can be used to measure levels of humidity or steam. Infrared therapy is often referred to as a type of sauna, but according to the Finnish sauna organizations, infrared is not a sauna. Areas such as the rocky Orkney islands of Scotland have many ancient stone structures for normal habitation, some of which incorporate areas for fire and bathing.
It is possible some of these structures also incorporated the use of steam in a way similar to the sauna, but this is a matter of speculation. The sites are from the Neolithic age, dating to approximately B. The traditional Korean sauna, called the hanjeungmak , is a domed structure constructed of stone that was first mentioned in the Sejong Sillok of the Annals of the Joseon Dynasty in the 15th century.
Western saunas originated in Finland where the oldest known saunas were made from pits dug in a slope in the ground and primarily used as dwellings in winter. The sauna featured a fireplace where stones were heated to a high temperature.
Water was thrown on the hot stones to produce steam and to give a sensation of increased heat. This would raise the apparent temperature so high that people could take off their clothes. The first Finnish saunas were always of a type now called savusauna ; "smoke sauna". A properly heated "savusauna" yields heat for up to 12 hours. As a result of the Industrial Revolution , the sauna evolved to use a wood-burning metal stove with rocks on top, kiuas , with a chimney. As the Finns migrated to other areas of the globe, they brought their sauna designs and traditions with them.
This led to a further evolution of the sauna, including the electric sauna stove, which was introduced in by Metos Ltd in Vaasa. The sauna became very popular especially in Scandinavia and the German-speaking regions of Europe after the Second World War. German soldiers had experienced Finnish saunas during their fight against the Soviet Union during the Continuation War , where they fought on the same side.
