You step out of the sauna and lower yourself into cold water. Your heart skips, just once.

Then you sit on a chair. Looking at the sky, or at the person next to you.

A few minutes pass, and something shifts.

The heat slowly leaves the body, from the inside out. The noise inside the head becomes a little softer. The palms feel warm. The fingertips, all the way to their ends, feel like part of the body again.

This sensation has a name in Japanese sauna culture: totonou. It means, roughly, "to be put in order."

Only recently has neuroscience begun to describe what is actually happening in those minutes.

Here is the story, told as quietly as the experience itself.

The body is stretched twice

Inside the sauna, the body is trying to escape the heat.

Blood vessels widen. Heart rate climbs. Sweat appears. The sympathetic nervous system — the "fight or flight" side — is dominant. The body is in active mode.

Then comes the cold water.

The opposite stimulus. Vessels constrict sharply. Heart rate spikes again. The sympathetic nervous system fires again, even more strongly than before.

A short immersion in water around 10°C can elevate plasma norepinephrine to two to five times its resting level (SweatDecks, 2026). Dopamine rises by roughly 250%.

Norepinephrine governs focus and alertness. Dopamine governs mood and motivation.

The body has been stretched twice. Once by heat. Once by cold.

And here, totonou has not yet arrived. The body is, in fact, at the peak of its tension.

The switch happens during the rest

You leave the cold water and sit down.

What happens next is probably the most important part.

The sympathetic nervous system, which was firing hard, quietly steps back. The parasympathetic system — the "rest and digest" side — takes over.

Vessels gently open again. Blood returns to the periphery. Heart rate slows. Breathing deepens.

This, researchers say, is the closest thing to totonou itself.

In 2023, Chang and colleagues measured the brainwaves of subjects before and after sauna sessions (PMC10681252).

After cycles of heat, cold, and rest, two changes appeared in the EEG.

The first: a marked increase in theta and alpha power. Theta waves are the slow rhythms of deep relaxation and meditation. Alpha waves emerge when the eyes are closed and the mind is calm.

The second: a reduction in the P300 component — the brain's response to external attention. It became smaller.

In other words: attention that had been pointed outward turned back inward. The brain entered observer mode.

It resembles the EEG of experienced meditators.

Totonou arrives on its own

What matters here is that this state cannot be forced.

Sitting in meditation, breathing deeply — these things rarely produce theta waves of this magnitude on their own.

But after a cycle of heat, cold, and rest, it happens. The body switches over by itself.

Chang and colleagues describe this as a state of being put in order. Not "putting yourself in order."

This may be why sauna culture has survived for two or three hundred years. Relaxation is not something the mind decides to produce. When you leave it to the body, it happens.

The afterglow of norepinephrine

There is another finding worth noting.

The norepinephrine released during cold exposure does not disappear right away. Plasma levels remain elevated for several hours afterward (Nomad Labs, 2026).

And elevated norepinephrine has measurable anxiety-reducing effects.

The sharp clarity you feel right after the cold plunge is the spike. But the quiet, focused hours that follow — those are the same molecule, persisting.

The way the world feels a little easier for the rest of the day after a sauna is not imagination. It is a neurochemical aftereffect.

Parasympathetic dominance, and the urge to talk

When the parasympathetic system is in charge, the body becomes unguarded. The face softens. The voice drops.

And, oddly, the urge to talk arrives.

After the sauna, you find yourself in a slightly longer conversation with the person who happened to sit next to you. You say things you would not normally say.

This is, perhaps, the social side effect of a parasympathetic state.

The Polyvagal Theory (Stephen Porges, 2011) describes how the ventral vagal complex — a specific branch of the parasympathetic system — governs human connection and feelings of safety. The reason people want to talk after the sauna may be that this circuit is more active than usual.

The sauna looks like a solitary practice. But what often follows is a quiet form of social presence.

And still, not everything can be explained

Having written this much, it feels strange to say what comes next.

The neuroscience cannot fully account for totonou.

Norepinephrine numbers, theta wave amplitudes — these can be measured. But the feeling of the world looking a little softer after the sauna does not appear on a graph.

The research tells you how it happens. Why it feels so good is something you can only understand by entering the heat yourself.

The reason this practice has stayed with people for so long is not that the science was figured out. People knew long before the studies came. They knew that moving between heat and cold leaves something different behind.

In Bali, the same thing happens

A small note to end on.

We run two sauna places in Bali. KAYUN, in the forest of Ubud. Hokkaido Icebath, on a rooftop in Kuta.

After the heat and the cold, in Ubud you can hear the forest. In Kuta you can see the sky.

While you are sitting there, all the things written above are quietly happening inside your body.

But we hope you come without knowing any of it. The theta waves and the norepinephrine — you do not need to know about them.

If you just sit on the chair and look at the sky, the body will tell you the rest.

That is what we have prepared the space for.

References

Chang et al. (2023). A study on neural changes induced by sauna bathing: Neural basis of the "totonou" state. PMC10681252.
Shinkai & Tomita (2025). Hydrogen sulfide and the physiology of "totonou". ScienceDirect.
Laukkanen, Lipponen, et al. (2019). Recovery from sauna bathing favorably modulates cardiac autonomic nervous system.
Porges, S. W. (2011). The Polyvagal Theory. W. W. Norton & Company.
Šrámek et al. (2000). Human physiological responses to immersion into water of different temperatures. European Journal of Applied Physiology.

The Neuroscience of Totonou — What Actually Happens After the Sauna