What happens to our body in and after sauna?

Human beings have always loved the warmth. There’s a good reason for that. In a temperate environment, we need less food to maintain our body heat. And it’s generally nice to be in a warm environment. Let’s explore what our body experiences in the sauna and how it affects how we feel when we leave the steam room.


We have always sought warmth to feel good

Northern people often travel south to escape our cold and gloomy winter or heat up a sauna. In either case, we seek warmth to feel good. However, the heat experienced in the sauna is unusually high.

All animals, including us humans, have evolved in a relatively small temperature range. Sauna temperatures of 158-212° F  (70–100 °C) are, of course, higher than anything we experience in nature, and because of this, our bodies cannot tolerate such heat for long. While in a sauna, the human body experiences all kinds of changes meant to keep the heat at bay.


A sauna triggers a fight-or-flight response in our bodies

Imagine being faced with a wild tiger. Your pulse goes up, and your palms start to sweat. This is your body preparing to fight or flee the danger. It may seem an odd comparison but taking a sauna bath similarly affects our physique.

Our body interprets the high temperatures of the steam room as a danger and automatically prepares to deal with it. The fight-or-flight reaction kicks in. No one is forcing us to go to the sauna, of course, so it is not quite the same as facing a tiger in the wild. Yet our body reacts much the same way. These changes affect our health and well-being during and after the sauna.



In the sauna, the heart beats like an athlete’s

Although we sit still in one place in the sauna, our heart reacts as if we were physically active.

This is because blood vessels dilate in a hot environment, and the heart needs to work hard to maintain normal blood pressure. The heart rate reaches 120 beats per minute, sometimes even 150 beats per minute, as if we were doing sports. These figures typically fall between 60–80 beats per minute in a relaxed state.

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Skin temperature as high as 41 °C (105.8 °F)

Perspiration takes time. You do not start to sweat the second you enter the steam room. Why so?

Well, even though your skin temperature will start to rise immediately and eventually reach 41 °C (105.8 °F), our body feels the need to cool itself only once the core body temperature has reached a rough 37 °C (98.6 °F). We may sit in the steam room for quite a while before that happens.

Soon enough, though, 70% of our body is wet from sweat.  Our core body temperature will rise 1 °C per minute, reaching as high as 39–40 °C (104 °F).  Due to this sharp rise in our core body temperature, we may sweat one and a half litres of water per hour.


Cognitive and motor skills in the sauna

Entering the steam room late at night, we feel already quite tired from all the hassle and bustle of the day’s activities. Sauna adds to this exhaustion and pressures our cognitive and motor skills. Our brain does not have enough resources to deal with the heat and solve complicated mental tasks simultaneously. It is inevitably programmed to focus all its energy on saving itself from the effects of high temperatures.

Try it yourself. Next time you are in the sauna, try writing your name in a mirror image. Or explain to your friends the theory of general relativity. If you are not a physics teacher or Leonardo Da Vinci (who liked writing in mirror images), these tasks will prove very-very tricky.


Why do we feel less hungry in the sauna?

You may have noticed that you don’t want to eat much in hot weather or when you have a fever. The same thing happens in the sauna. A hormonal change in your body is to blame. The hormones regulating our appetite cannot work properly when the outside temperature hits 30 °C (86 °F). Such heat raises leptin levels in our blood, reducing hunger, even if we have not eaten much.




A sauna helps a body to recover

If you are one of those whose feet and hands often get cold, you probably also know the cause is insufficient blood supply. While in the sauna, the blood vessels expand due to the heat. Dilated veins allow blood to flow more easily from the middle of the body to the arms and legs.

The sauna’s heat improves the blood supply to the hands and feet. Also, with the help of red blood cells, more oxygen moves to these areas. Oxygen is indispensable to produce the energy muscle cells need and make our body move.

As a result of good blood supply, metabolic residues, and carbon dioxide deposited there during the day are removed from the muscles. The sauna helps the body recover only if there is enough oxygen-rich air in the steam room to breathe.

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Sauna improves your sleep

Taking a sauna or a warm bath before bed helps us fall asleep more quickly, shortening the time to fall asleep by almost nine minutes and ensuring a deeper sleep.

This is how it’s explained. In the intense heat of the steam room, our blood rushes to the skin and limbs to help with cooling. Once we exit the sauna, the body cools down very quickly. And this drop in body temperature lets the brain know it is time to hit the sack.

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Sauna vs. viruses

Many viruses cannot stand high temperatures. This is good news for all who like saunas since the sauna’s heat is intense enough to kill many viruses that harm us.

The air we breathe in kills the viruses in the upper airways. In addition, the steam rising from the stove raises the relative humidity, which helps restore the mucus of the airways. As a result, our body is better prepared to fight off viruses also after the sauna.

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Our body experiences a series of changes during and after the sauna session. All of them are mediated by our sympathetic nervous system, which interprets a hot sauna as threatening our life and health. The fight-or-flight response is triggered.

To save the body from overheating, we start sweating, our blood vessels expand, and the heart is forced to pump blood faster. The brain gets busy coordinating survival, so at the same time, our mental acuity isn’t precisely brilliant on the sauna stage. Relaxation and a night of good sleep are guaranteed after leaving the sauna.


Based on:

Hõbepappel, Urmas; Hõbepappel, Liisa; Nellis, Silja; Nellis, Siim. Suur sauna raamat. Tartu, (manuscript)

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