Finnish sauna

The savusauna (smoke sauna) is a special type of sauna without a chimney. Wood is burned in a particularly large stove and the smoke fills the room. When the sauna is hot enough, the fire is allowed to die and the smoke is ventilated out. The residual heat of the stove is enough for the duration of the sauna. This represents the ancestral type of sauna, since chimneys are a later addition. Smoke saunas have experienced great revival in recent years since they are considered superior by the connoisseurs.[7] They are not, however, likely to replace all or even most of the regular saunas because more skill, effort, and time (usually most of the day) are needed for the heating process.[8]

Smoke saunas are still extant not only in Finland but also in Estonia, Latvia, and Lithuania. They are considered to be cheap, simple to build, and durable (if measures of fire prevention are taken while building the sauna). The longevity is warranted by disinfectant features of smoke.

One specific and rarely seen curiosity is use of a wood pellet burner to heat a smoke sauna stove, typically the actual burner installed into a room adjacent to the actual sauna room and the kiuas. A wood pellet burner, quite similar to an oil burner, is then used to heat a smoke sauna stove - practically a big pile of rocks. As the burning process is much cleaner than with a conventional smoke stove the smoke aroma is much less pungent and soothy, while the moisture produced by the burning the pellets makes the air more pleasant than with continuously warmed stoves.

The wood stove sauna is the most common type of sauna outside of the city areas, where the electric sauna is more common. The metal stove with stones on top (kiuas) is heated with birch wood fire, and this heats the sauna room to the required temperature. If birch wood is not available any other wood will do, but well dried birch wood is preferred because of its good quality and smell, and long lasting burn. The important thing is to have a good löyly, that is when the stones are hot enough to evaporate the water thrown on them into steam that rises to the bathers. The bather in every type of sauna sits on a high bench near the ceiling where the hot steam reaches them quickly.

In city apartments, and in most public saunas, an electric sauna stove (kiuas) is used, as it does not require wood to burn. They are very simple to prepare, only a press of a button will do. They usually have stones to retain heat, like their smoke sauna and wood stove counterparts, but sometimes even a large slab of stone is used to give the same effect as you throw water on it. Most apartment buildings in Finland include at least this type of sauna, or there is one for use by the occupants of a building, with dedicated hours for use for communal men's and women's sauna, and special hours for those who have requested apartment specific hours. Most Finns prefer a wood stove sauna to an electric sauna.

Scouts and various other youth organizations often have portable tent saunas. Saunas have been built into cars, buses, car trailers, tractor trailers or even bicycles and boats.[9] In Finland, there are companies that rent mobile saunas,[10] and an annual mobile sauna event in Teuva.[11]

The 2020 pandemic of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) caused by the virus COVID-19 renews interest in the role temperature plays in our immune response. A febrile response to an infection has been demonstrated to be a protective mechanism, rather than a symptom of infection, and is associated with better survival and shorter duration of disease. [12] Unpublished data that is suggestive of a role for thermal manipulation (similar to what occurs during a Finnish sauna) in the COVID-19 pandemic shows reduced rates of infections and reduced deaths in Finland when compared to neighbouring countries possibly implicating the Finnish sauna for the positive associations in these observations. This information is compiled and presented on 30 March 2020 by Seheult suggests a reduction in the total cases/million population and a reduction in total deaths in Finland (224 infections/million, 11 deaths) where Finnish sauna is common compared to neighboring Sweden (366 infections/million, 110 deaths), Norway (787 infections/million, 25 deaths), and Denmark 413 infections/million, 72 deaths), countries where sauna is not as popular (many confounding variables were not controlled between these countries that could influence these results). In addition March 2020 was very early in the progress of the infection. Note also that Norway's fatality rate was better than Finland's. A randomized controlled trial needs to be done to evaluate the influence of thermal manipulation, such as occurs during Finnish sauna, on SARS-CoV-2 outcomes. [13]

Multiple small studies over the past two decades have suggested a positive response on the immune system with thermal manipulation. [14] In the study by Zellner, a small group (twelve test subjects) were exposed to a hot water bath of 39.5 degrees Celsius to raise core body temperature in order to determine the influence of hyperthermia on monocytes. Monocytes are important for the recognition and elimination of pathogens in the immune response. This study concluded that the thermal effect of fever activates monocytes. Monocytes have been found to be deficient in patients with COVID-19 infection.

In another study [15] subjects core body temperatures were increased followed by cooling. An increase in monocytes was noted, among other positive findings, indicating stimulation of the innate immune response.

Ernst demonstrated regular use of a sauna over a 6 month period showed a reduction in the frequency of common cold symptoms. [16].

The innate immune response refers to the early response of the immune system and is our first line of defense against an infection prior to the later activation of T-cells and B-cells in the complicated immune cascade. A successful innate immune response should be able to suppress viral replication at an early stage of infection. This is where COVID-19 may evade our immune response in patients who are seen to do poorly, evidenced by low monocytes. By blunting the early innate immune response, the body is set up for a "cytokine storm" later in the infection. This may explain why patients initially seem asymptomatic until later when there is an abrupt release of inflammatory cells. The incubation period for the current SARS-COV-2 is believed to be up to 14 days during which patients are generally asymptomatic or have mild symptoms. Compare this to influenza which has 1-4 day incubation period. The subsequent cytokine storm can cause lung injury and sepsis requiring hospitalization and poor outcomes. This early response to infection is mediated in part by type 1 interferon which acts to prepare uninfected neighboring cells to fight a possible infection. Without type 1 interferon, activation of the later immune response is blunted and viral replication is uncontrolled. In the review article by Prompetchara[17], SARS-CoV (in 2002) and MERS-CoV (in 2011) have shown a delayed or suppressed type 1 interferon response. The viruses causing these earlier epidemics (SARS-CoV and MERS-CoV, respectively) show a similar genomic sequence to the current SARS-CoV-2. The response of the immune system to COVID-19 may therefore be similar. Young children have a highly effective innate immune response which may explain their seeming resistance to SARS-CoV-2.

The term thermal manipulation is a more adept term since thermal regulation refers to the body's own response generated internally whereas thermal manipulation is the external intentional influence on core body temperature.