"It's an onsen, but it's cold." Have you ever had such an experience? In fact, according to Japan's Onsen Law, water at 25°C or above is recognized as an "onsen." This means that even if it's cold, it's still considered an onsen.
Japanese onsens have a wide range of temperatures, from cold springs to high-temperature hot springs. These temperature differences influence the unique characteristics and benefits of each onsen.
Temperature Classification According to the Onsen Law
The Japanese Onsen Law classifies onsens into four categories based on temperature.
Cold Spring: Below 25°C
Low-Temperature Onsen: 25°C to below 34°C
Onsen: 34°C to below 42°C
High-Temperature Onsen: 42°C and above
Further detailed classification is as follows:
- Cold Mineral Spring: Below 25°C
- Tepid Onsen: 25°C to below 34°C
- Onsen: 34°C to below 42°C
- Hot Onsen: 42°C to below 50°C
- High-Temperature Onsen: 50°C and above
Temperature Conditions of Japanese Onsens
Most Japanese onsens fall under the categories of "onsen" or "high-temperature onsen," meaning they are 34°C or above.
However, cold springs and low-temperature onsens also exist, often found in areas with weak volcanic activity or where deep underground water surfaces.
Cold Springs (Below 25°C)
Cold springs are onsens with temperatures below 25°C. Although "cold onsen" might sound unusual, they are legitimate onsens.
Characteristics of Cold Springs
Temperature: Below 25°C, lower than body temperature.
Bathing Method: Entering as is can feel cold. Many facilities heat the water before offering it.
Benefits: Due to the low temperature, long bathing is possible with less strain on the heart.
Examples: Goshiki Onsen (Nagano Prefecture), Oku-Nikko Yumoto Onsen (Tochigi Prefecture, some parts).
Enjoying Cold Springs
Entering a cold spring without heating can be refreshing and stimulating. In summer, cold onsens feel particularly pleasant.
Additionally, cold springs are often suitable for drinking. The low temperature makes them easy to drink.
Low-Temperature Onsen (25°C~34°C)
Low-temperature onsens are lukewarm, cooler than body temperature but not cold.
Characteristics of Low-Temperature Onsens
Temperature: 25°C~34°C, lukewarm.
Bathing Method: Suitable for long baths. High relaxation effect.
Benefits: Stimulates the parasympathetic nervous system, promoting relaxation and lowering blood pressure.
Examples: Naruko Onsen (Miyagi Prefecture, some parts), Yuda Onsen (Yamaguchi Prefecture).
Enjoying Low-Temperature Onsens
You can soak in low-temperature onsens for 30 minutes to an hour. Enjoy a book while leisurely soaking in the onsen for the ultimate relaxation experience.
Onsen (34°C~42°C)
This is the most common temperature range for onsens. It's the temperature that Japanese people find "just right."
Characteristics of Onsens
Temperature: 34°C~42°C, comfortable temperature.
Bathing Method: A 10~15 minute bath is appropriate.
Benefits: Promotes blood circulation, relaxation, and fatigue recovery.
Examples: Most onsens fall within this temperature range.
What is the Ideal Temperature?
The temperature that Japanese people find most comfortable is around 39~41°C. At this temperature, the parasympathetic nervous system becomes dominant, allowing for relaxation.
When the temperature exceeds 42°C, the sympathetic nervous system is stimulated, leading to a state of excitement.
High-Temperature Onsen (42°C and above)
These are hot onsens. Japan has many very high-temperature onsens.
Characteristics of High-Temperature Onsens
Temperature: 42°C and above, hot.
Bathing Method: Short baths (5~10 minutes). Long baths are not possible.
Benefits: Stimulates the sympathetic nervous system, awakening effect, strong sweating effect.
Examples: Kusatsu Onsen (Gunma Prefecture, source temperature above 50°C), Atami Onsen (Shizuoka Prefecture).
Enjoying High-Temperature Onsens
High-temperature onsens are enjoyed for the "hot!" stimulation. Take short baths and rest in between. Repeat this process.
In some cases, high-temperature onsens are cooled by "yumomi" (stirring the water). Kusatsu Onsen's "yumomi show" is famous.
Onsens with Extremely High Source Temperatures
In Japan, there are onsens with source temperatures close to 100°C.
Tamagawa Onsen (Akita Prefecture): Source temperature 98°C. Also known for its strong acidity with a pH of 1.2.
Kusatsu Onsen (Gunma Prefecture): Source temperature around 50~80°C. Too hot to use directly, requiring dilution or cooling.
These onsens cannot be used directly from the source. Dilution or cooling is necessary.
The Relationship Between Temperature and Benefits
The temperature of an onsen greatly influences its effects on the body.
Tepid Water (34°C~39°C)
Effects: Stimulates the parasympathetic nervous system, promoting relaxation and lowering blood pressure.
Recommended Time: Before bedtime. When you want a long bath.
Optimal Temperature Water (39°C~42°C)
Effects: Promotes blood circulation, fatigue recovery, balanced benefits.
Recommended Time: Anytime. The most versatile temperature.
Hot Water (42°C and above)
Effects: Stimulates the sympathetic nervous system, awakening effect, sweating effect.
Recommended Time: Morning. When you want to wake up.
Temperature Preferences Vary by Person
Preferences for onsen temperatures vary among individuals.
People who like hot water: Feel that "it's not an onsen if it's not hot."
People who like tepid water: Think "I want to soak for a long time."
Both are valid. Choose an onsen with a temperature that suits your preference.
Choosing an Onsen by Temperature
Many onsen facilities display the source temperature and bath temperature. Use this information to choose an onsen with a temperature that suits you.
For relaxation: Tepid water (34°C39°C)42°C)
For balance: Optimal temperature water (39°C
For stimulation: Hot water (42°C and above)
Conclusion
Japanese onsens have a wide variety of temperatures, from cold springs to high-temperature hot springs.
Temperature greatly influences the effects on the body. Tepid water offers relaxation, while hot water provides an awakening effect. Choose an onsen with a temperature that matches your purpose.
Even "cold onsens" are legitimate onsens. Enjoying the differences in temperature is part of the charm of Japanese onsens.
