Based on Professor Lasse Viinikka’s talk at SaunaExpo in April 2009.
The first scientific study on saunas dates back to 1765, when physician Anton R. Martin from Stockholm visited the border areas of Vyborg Governorate to study the region’s saunas. This is the oldest publication about the health effects of saunas, and it states that:
– The smoke from saunas causes ingrown hairs around the eyes.
+ The skin temperature rises to 38–39 degrees on the Swedish scale.
+ The pulse rises up to 130 beats per minute.
– Delicate children’s pulse could not be taken, but their respiratory rate was 150–160 breaths a minute.
– Reduced lactation in women.
+ Reduced amount of urine.
+ After hard work, a bather feels happy and limber again.
– The human body stretches by an inch in the sauna. – Excessive bathing of children in Finland is the reason behind the commonly occurring constipation.
– The sauna makes people flabby, causing the most avid bathers to look older than they are. (Martin, Kongl. Sv. Vet. Acad. Handl., Jan, Feb, Mart, 1765, 69.)
Some things may be true
Based on what we now know, four of these ten observations are correct. However, it is not hard to imagine that any research results we get today will have a similar accuracy rate when observed 250 years from now.
The skin’s temperature and heart rate will rise while bathing in a sauna.
The amount of urine decreases, as water is lost through sweating.
And the sauna does help relax sore muscles.
The rest of the statements are incorrect. In fact, sauna bathing increases the amount of the hormone that causes lactation, although this has not been shown to have any practical effect. And finally, sauna bathing does not make you look older.
The number of publicly available studies on the physiological and medical effects of the sauna is somewhere between 400 and 500.
Significant changes in circulation
The health benefits of the sauna are relatively well known, as 14 or 15 dissertations have been written about them in Finland alone. The most significant changes in the body during sauna bathing affect the circulation. In room temperature, around 10% of the blood pumped by the heart goes to the skin. But in hot temperatures the skin warms up, causing the vessels to dilate and subsequently the overall volume of the vessels to increase. As much as 70% of the blood may circulate via the skin while in the sauna. The opposite happens when the temperatures drop.
In order to compensate for the increased volume of the blood vessels, the heart begins to beat faster, because otherwise the body’s blood pressure would drop to an unsustainable level. The vessels’ dilation causes redness of the skin. Artists have also captured this phenomenon, for example Eero Järnefelt, whose painting Kylpylakana depicts a girl with beautifully rosy cheeks.
Winter swimming has its risks
Swimming after the sauna makes the skin’s blood vessels contract, and the blood pressure quickly rises relatively high. A healthy person can usually cope well, but an increase in blood pressure may be dangerous to individuals suffering from heart failure, causing weakness in the heart or serious arrhythmia. However, few people in Finland die while bathing in the sauna or swimming in cold water considering how common both of these practices are.
‘People often ask what the main health effect of the sauna is. The answer depends on how we value things. Temporary effects on the circulation have little impact on our overall health. Therefore, I usually reply that the biggest health benefit of the sauna is the relaxation it offers. This is a scientifically proven fact, and all Finns are familiar with it,’ says Lasse Viinikka.
An increase in the feel-good hormone
The mechanism behind the relaxing effects is not yet fully understood. However, two explanations have been proposed, and they are not mutually exclusive.
The first one is biochemical. Bathing in the sauna increases the release of the feel-good endorphins in the brain. Some studies have identified this phenomenon, while others have not. These findings are not particularly reliable, because the creation and effects of endorphins take place in the brain where they cannot be measured, and using blood to study these hormones involves several potential causes for errors.
The second is psychological. Psychoanalysts believe that the warm and calm atmosphere of the sauna – as well as the dark shades and pleasant scents of a chimneyless sauna – take us back to our childhood, even as far as our mother’s womb, making us feel good.
At first glance, these two hypotheses are conflicting, but this might not be the case: if the level of endorphins is sufficiently high, the positive sensations may take the mind back to the golden years of childhood.
Heart attacks do not increase
The sauna is the hottest place where a person will go voluntarily. Because of this, foreigners who are unfamiliar with the concept feel particularly suspicious about it. One example was a British military doctor who once questioned the safety of saunas in a highly prestigious medical publication. At the time, Finland had the highest number of deaths due to heart attacks, and as the nation was also the most frequent users of the sauna, the doctor drew a conclusion that sweating in the sauna thickens your blood, which may lead to a heart attack.
As a result, Finnish researchers quickly began to investigate these claims. A handful of studies were meticulously carried out on deaths caused by bathing in the sauna, but they all concluded that the practice does not increase the risk of death by heart attack.
Drunkenness and sauna do not mix
Those who die in the sauna are typically inebriated – as many as half of the cases, according to some studies. Being drunk may lead a person to slip on the sauna floor or forget to be mindful of an underlying heart problem, potentially resulting in arrhythmia from too much heat. In addition to that, an inebriated person can also fall asleep in the sauna and become dehydrated.
The recommendation not to bathe in the sauna while drunk is not so much about the social norms but about a clear danger shown to exist through medical research.
The sauna is fine for expecting mothers
The fact that the sauna is so hot has caused some in foreign countries to question its safety. In the 1970s, people were wondering whether the sauna causes developmental problems. The risk of being born without a brain, a rare and serious birth defect, was suspected to rise due to bathing in the sauna. Five of the mothers included in the studies had had a fever, and two had bathed in the sauna. References were also made to a research finding that stated that increasing the temperature also increased the risk of defects in the central nervous system amongst pregnant laboratory animals.
Later, an American study comprising approximately 23,000 people came to the same conclusion, but a closer analysis of the findings showed that they all fitted within the margin of error.
Finns, once again, began to study these hypotheses, but no differences were discovered in comparison to the control material.
The general consensus in Finland is that bathing in the sauna during pregnancy is safe. The central nervous system defects described above are rare in Finland, even though nearly all pregnant women use the sauna throughout their pregnancy.
Relief for asthma
Can the sauna stop you from getting a cold? A scientific study from Austria claims that sauna bathing can reduce the likelyhood of a cold by up to 30%. However, the study does have certain shortcomings, and no known biochemical mechanism exists to explain why this should be. Furthermore, there are no other research findings on this.
The sauna helps with asthma by dilating the bronchi, but anyone allergic to birch trees should avoid using a sauna whisk made from birch. Additionally, people who suffer from rheumatism have reported that the pain occasionally reduces on the day of sauna bathing, but the following day it may become worse.
Lower blood pressure
The extensive studies carried out amongst heart failure patients in southern Japan on the sauna and the heart have been some of the most intriguing ones in recent years. During sauna bathing, the subjects had reduced blood flow resistance in the heart, the heart pumped more efficiently, the blood pressure was reduced and the heart became smaller. The subjects felt better, meaning that their heart was also in a better condition.
It could therefore be concluded that the sauna puts a similar stress on the circulatory system organs as a brisk walk. If a heart patient is able to walk without getting out of breath, they will also be able to bathe safely in the sauna.
The sauna and cardiovascular diseases
Based on a talk given at the International Sauna Congress in 2006 by Katriina Kukkonen-Harjula (PhD), a docent and senior researcher at the UKK Institute.
Hormones and medication
Sauna bathing causes short-term changes in the secretion of hormones in healthy people (Hannuksela and Ellahham, 2001), with the purpose of maintaining a balance in the body. Some of these changes are similar to other stress inducing situations, while others are typical for the sauna. In particular, the amount of growth hormone and prolactin in the blood increases. Bathing in the sauna can cause either pleasant or unpleasant feelings, although the more used to the sauna we are, the milder these effects become. Usually, the hormone levels in the bloodstream return to their previous levels within a few hours after the sauna.
Few studies comparing the effects of different sauna bathing styles on healthy or sick individuals have been carried out. In our study (Kukkonen-Harjula et al., 1989), healthy young men stayed in a relatively hot (80 ºC) or hot (100 ºC) sauna without throwing any water onto the stones for as long as they felt comfortable doing so. Some changes occurred in their circulation and hormone secretion, but to a lesser degree when compared to bathing until exhaustion (at 80 ºC) while also throwing water onto the heater’s stones.
Unfortunately, whether there is any connection between hormones and the sense of relaxation and wellbeing, often associated with the sauna, remains unclear. Neurotransmitters may provide some explanation, as they have been found (without sauna bathing) to have a link to reduced stress and anxiety, higher pain threshold and improved growth and tissue healing. This could explain the psychological and social effects of bathing in the sauna, but no research data exists on any changes in the hormone levels in circulation due to sauna bathing.
Simultaneous use of medication and bathing in the sauna may, theoretically, cause problems, as the heat accelerates circulation and sweating affects the body’s fluid balance. Because of these factors, medication may be absorbed, distributed around the body, metabolised and excreted differently than normal, resulting in changes in how the medication affects the body. Few studies have been carried out on the impact of the sauna on the effectiveness of medication, and most of the studies have used healthy volunteers. The most extensive ones include Vanakoski’s dissertation (Vanakoski, 1996) and Vanakoski and Seppälä’s reviews (1996, 1998).
The most commonly used medication during sauna include various forms of heart and circulatory system medicines. A moderate amount of sauna bathing does not usually put too much strain on the circulatory system, as long as the person is receiving adequate treatment for their coronary artery disease (Luurila, 1992), hypertension or heart failure. Beta blockers slow down the heartrate, both during rest and physical exertion, as well as during sauna (Luurila et al., 1989). They also lower the blood pressure, particularly after the sauna, which may occasionally lead to dizziness. If that is the case, it may be prudent to avoid taking beta blockers a few hours before going to the sauna. Apparently, newer heart and blood pressure medication that utilises different mechanisms do not cause similar problems while bathing in the sauna. Many Finnish heart patients have found that the sauna can cause a similar effect with nitrovasodilators: the heat dilates the blood vessels, and therefore patients can usually skip a dose before the sauna.
Any medical plasters should be removed before bathing in the sauna, as they might become detached anyway due to sweating, showering or swimming. After the sauna, make sure that the replacement plaster is firmly attached to the skin. It is worth noting that the sauna does not tend to cause any issues with oestrogen patches used as contraceptives (Zacur et al., 2002). These hormonal patches release the medicinal product slowly, which is why bathing in the sauna will not interfere with them in any way. Similarly, the oestrogen in patches used to treat symptoms of menopause have an extensive therapeutic area, and therefore it is safe to leave the patch on while bathing. No data exists on the effectiveness of patches against motion sickness when used in the sauna, but travellers often use them in hot climates as well. (Kukkonen-Harjula et al., 1994.)
In other words, sauna bathing rarely causes any problems with medication. The most likely reason is that the exposure to heat is relatively short in duration and any changes in the body return back to normal within a few hours after a bathing session. Any harmful combination effects only appear under special conditions (e.g. medication given via the skin or medication that makes the sympathetic nervous system work faster). No research data currently exists on any harmful effects on people taking neuroleptics or antidepressants. These medicines may have an effect on heat regulation and the functioning of the autonomic nervous system. Another interesting theoretical area would be to study the effects of sauna bathing on asthma medication.
The information on the page was compiled by Raili Vihavainen.