Exiting the sauna, you step into the cold plunge bath. At that moment, the cold water envelops your entire body. The first 5 seconds are a shock. By 10 seconds, you start to acclimate, and by 30 seconds, it becomes comfortable. Then, after leaving the cold plunge bath, the outdoor air bath brings about the 'totonou' experience.

In Japanese sauna culture, the cold plunge bath is one of the main attractions. Sauna, cold plunge bath, and outdoor air bath—only when these three elements are combined does a perfect sauna experience occur.

Why are Cold Plunge Baths Emphasized in Japan?

In Finnish saunas, people dive into lakes or snow after the sauna. They use natural cold water, and the experience changes with the seasons. On the other hand, Japanese saunas have cold plunge baths permanently installed within the facilities, allowing for a consistent experience with temperature-controlled cold water all year round.

Japan has long had a culture of alternating between hot springs and cold water baths, known as 'alternating hot and cold baths.' Saunas have also merged with this culture. Additionally, since many Japanese saunas are located in urban buildings without natural lakes or rivers, artificial cold plunge baths have developed.

Furthermore, the Japanese commitment to quality has elevated the temperature, water quality, and cleanliness of cold plunge baths to the extreme.

The Temperature of Cold Plunge Baths: Differences in Sensation

When visiting sauna facilities nationwide, you'll find that the temperature of cold plunge baths varies greatly by facility. Understanding the differences in sensation due to temperature is important.

Extremely Cold (Below 10°C)

Intensely cold. Suitable for advanced users. It provides the strongest stimulation and maximum blood vessel constriction. However, it can be taxing on the heart, so prolonged exposure is dangerous. I have experienced it several times, and staying in for more than 10 seconds required considerable resolve.

Cold (10–14°C)

Quite cold and requires acclimation. It offers strong stimulation and allows for a deep 'totonou' experience. For sauna enthusiasts, this is the ideal temperature range. It is my favorite temperature. Notable cold plunge baths like the 11.7°C at Kobe Sauna and the 14°C at New Japan Umeda fall within this range.

Standard (15–17°C)

Cold but bearable. It provides moderate stimulation and is the most balanced temperature range. Many sauna enthusiasts consider this the ideal temperature. It is the easiest to feel 'totonou.' Discovering this temperature at a new facility raises expectations.

Slightly Cold (18–20°C)

Feels cold to some extent. It offers mild stimulation and is recommended for beginners. However, as you become accustomed to saunas, it may start to feel a bit lacking.

Lukewarm (21°C and above)

Not very cold. The stimulation is weak and may be unsatisfactory for sauna enthusiasts. It's unfortunate not to be able to properly cool down a body heated in the sauna.

The Importance of Water Quality in Cold Plunge Baths

Water quality greatly influences the satisfaction of a cold plunge bath.

Tap Water

The most common type. It is disinfected with chlorine and feels ordinary. It's not bad, but it doesn't offer any special excitement.

Groundwater

Some facilities use natural water drawn from underground. It is minimally disinfected, feels soft, and has a pleasant texture. It's noticeably different from tap water.

Natural Spring Water

The highest quality. It uses natural spring water with almost no disinfection. It feels mellow and incredibly soft to the touch. There's no chlorine smell, allowing for extended immersion.

The Impact of 'Drinkable Cold Plunge Baths'

Some sauna facilities in Japan boast 'drinkable cold plunge baths.' They use natural groundwater or spring water with minimal processing, constantly flowing fresh water.

The shock of entering a 'drinkable cold plunge bath' for the first time is unforgettable. It feels like being wrapped in natural silk. It is gentle on the skin, allowing for prolonged immersion. You can experience a deeper 'totonou.'

The cold plunge bath at Spa Alps (Toyama) using Northern Alps natural water was a supreme experience. The wild style of drinking natural water directly in the cold plunge bath is addictive.

The Correct Way to Enter a Cold Plunge Bath

Always Rinse Off Sweat

Before entering the cold plunge bath, always rinse off sweat. This is an absolute etiquette. After leaving the sauna, rinse off sweat with a shower or by pouring water over yourself, using your hands to wipe off sweat.

Why is this important? It is not only hygienic and considerate of others but also protects the water quality and keeps the cold plunge bath clean. Additionally, having sweat on your body makes it harder to cool down, which is a practical reason.

Pour Water Starting from Areas Distant from the Heart

Jumping straight into the cold plunge bath is dangerous. First, pour water on your feet, then your hands, arms, legs, and body in that order, gradually acclimating your body to the cold water.

Enter Slowly

Descend the steps or slowly immerse your feet. Submerge up to your knees, then your waist, and finally your shoulders. Jumping in is dangerous and bothersome to others.

Stay Still

Remain still while bathing. Breathe deeply and slowly. Close your eyes and relax.

The first 10 seconds are intensely cold and shocking, but between 10 and 20 seconds, a thin membrane forms around your body. This 'water membrane' acts as insulation, and after 20 seconds, you start to feel slightly warmer. Understanding this phenomenon can greatly change your cold plunge bath experience.

Exit at the Appropriate Time

For beginners, 30 seconds to 1 minute is a guideline, for those accustomed, 1 to 2 minutes, and for advanced users, 2 to 3 minutes. Exit when you feel sufficiently cooled before feeling too cold. It's important not to overdo it.

For Those Who Dislike Cold Plunge Baths

Many people dislike cold plunge baths. There's no need to force yourself, but it's recommended to challenge yourself gradually.

Start by just dipping your feet in. Sit on the edge of the cold plunge bath and submerge only below your knees. 1 to 2 minutes is enough.

Next, sit on the steps of the cold plunge bath and submerge up to your waist. 2 to 3 minutes.

Once accustomed, immerse your entire body for only 30 seconds. Gradually extend the time.

The key is breathing. Continue deep breathing. Inhale through your nose, exhale through your mouth. Focusing on your breathing makes the cold less noticeable. Gradually, without forcing it, extend the time a little each time.

Health Benefits of Cold Plunge Baths

In the sauna, blood vessels expand, in the cold plunge bath, they constrict, and during the outdoor air bath, they expand again. This cycle of blood vessel expansion and contraction greatly promotes circulation.

Additionally, the sauna promotes sympathetic nervous system dominance (excitement), the cold plunge bath reaches peak sympathetic nervous system activity, and the outdoor air bath switches to the parasympathetic nervous system (relaxation). This switching balances the autonomic nervous system.

The hot and cold stimulation activates the immune system, promotes the elimination of fatigue substances through improved circulation, and adaptation to cold water enhances stress resistance.

Etiquette for Cold Plunge Baths

There are five basic rules: always rinse off sweat (most important), enter quietly (do not jump in), do not submerge your head, do not monopolize for long periods, and do not contaminate the water.

Always tie up long hair. Floating hair in the cold plunge bath is unacceptable. Completely rinse off shampoo suds before entering. These are considerations for other users and etiquette that sauna enthusiasts should observe.

How to Find Facilities with Notable Cold Plunge Baths

Check if they use groundwater or natural water, whether it's a flowing or circulating system, and if they advertise 'drinkable cold plunge baths.' The ideal temperature is 15–17°C. The water should be clear, and the chlorine smell should not be strong. Depth is also important, with deeper being better (able to submerge up to the shoulders).

Sauna-specific review sites, posts by sauna enthusiasts on social media, and apps like 'Sauna Ikitai' are sources of information.

Winter Cold Plunge Baths: The Ultimate Experience

Winter cold plunge baths are special. In summer, an 18°C cold plunge bath may drop to 14°C in winter. With an outside temperature of 0°C, a 15°C cold plunge bath can actually feel warmer, creating a reversal effect.

Moving from a winter cold plunge bath to a cold outdoor air bath. This combination creates the deepest 'totonou.' A winter sauna trip is worthwhile for this experience alone.

Conclusion: Cold Plunge Baths are a Treasure of Japanese Sauna Culture

Cold plunge baths are an essential element of Japanese sauna culture. Warming up in the sauna, cooling down in the cold plunge bath, and 'totonou' in the outdoor air bath. This perfect three-step process is the essence of Japanese sauna culture.

It may be intimidating at first. It may be too cold to enter. However, once you experience the comfort of a cold plunge bath, there's no turning back.

A quality cold plunge bath feels like being wrapped in natural silk. Soft, gentle, and deeply relaxing.

When visiting Japan, be sure to experience a cold plunge bath. Step into the world of 'totonou.'