When you soak in a hot spring, you might feel a tingling sensation on your skin. Alternatively, it might feel slippery and soft. What causes this difference? The answer lies in the pH level.
Japanese hot springs boast an incredibly diverse range of pH levels, from the world's most acidic to Japan's most alkaline springs. This wide range of pH levels contributes to the unique characteristics of Japanese hot springs.
What is pH?
The pH level is a numerical measure that indicates whether a liquid is acidic, neutral, or alkaline, ranging from 0 to 14.
pH 7: Neutral (pure water) Below pH 7: Acidic (the lower the number, the stronger the acidity) Above pH 7: Alkaline (the higher the number, the stronger the alkalinity)
Lemon juice has a pH of about 2, while soapy water has a pH of around 10.
Classification of Hot Springs by pH
According to Japanese hot spring regulations, hot springs are classified into three categories based on pH levels.
Acidic: Below pH 3 Neutral: pH 3 to below pH 6 Alkaline: pH 6 and above
Further breakdown is as follows:
- Strongly Acidic: Below pH 2
- Acidic: pH 2 to below pH 3
- Weakly Acidic: pH 3 to below pH 6
- Neutral: pH 6 to 7.5
- Weakly Alkaline: pH 7.5 to 8.5
- Alkaline: pH 8.5 to 10
- Strongly Alkaline: Above pH 10
Japanese hot springs can be found across this entire spectrum.
Japan's Extreme pH Hot Springs
Japan is home to some of the world's most extreme pH hot springs.
Japan's Most Acidic Hot Spring: Tamagawa Onsen in Akita Prefecture, with a pH of 1.2. Tsukahara Onsen in Oita Prefecture has a pH of 1.4.
Japan's Most Alkaline Hot Spring: Hakuba Happo Onsen in Nagano Prefecture, with a pH of over 11.5.
This range showcases the diversity of Japanese hot springs.
pH Levels and Their Effects on the Skin
The pH level significantly influences the effects on your skin.
Acidic Hot Springs (Below pH 3)
Effects on Skin: Tingling sensation. High antibacterial properties.
Characteristics: Strong acidity kills bacteria and tightens the skin surface.
Recommended for: Treating skin conditions, athlete's foot, etc.
Caution: Strong stimulation. Avoid long soaks. Rinse with fresh water afterward.
Neutral Hot Springs (pH 6 to 7.5)
Effects on Skin: Minimal irritation. Gentle on the skin.
Characteristics: Close to the pH of human skin. Suitable for long soaks.
Recommended for: Sensitive skin, children, the elderly.
Caution: None. Safest for bathing.
Alkaline Hot Springs (Above pH 8.5)
Effects on Skin: Slippery, smooth. Removes dead skin cells.
Characteristics: Alkalinity softens and dissolves dead skin cells, creating a soapy feel.
Recommended for: Those seeking beauty benefits. People with dry skin.
Caution: Removes skin oils, so moisturize after bathing.
The Relationship Between pH and Spring Quality
pH levels are closely related to the quality of the spring.
Acidic Springs: Mostly strongly acidic to acidic. Contains sulfur or sulfuric acid.
Sulfur Springs: Often acidic to weakly acidic. Some are weakly alkaline.
Simple Springs: Mostly weakly alkaline, around pH 8 to 9.
Bicarbonate Springs: Almost all are alkaline, known as "beauty baths."
Chloride Springs: Mostly neutral to weakly alkaline.
Choosing Hot Springs by pH
Knowing the pH level helps you choose the right hot spring for you.
For Stimulation: Acidic hot springs (below pH 3). Tamagawa Onsen, Kusatsu Onsen, etc.
Gentle on Skin: Neutral hot springs (pH 6 to 7.5). Many simple springs.
Beauty Benefits: Alkaline hot springs (above pH 8.5). Gero Onsen, Hakuba Happo Onsen, etc.
Measuring pH Levels
The pH level of a hot spring is listed in the hot spring analysis report.
Every hot spring facility displays this report, which includes the pH level. Check it before entering the bath.
You can also bring pH test strips to measure it yourself, making for an interesting experience.
Changes in pH Levels
The pH level of a hot spring can change.
The Further from the Source: Exposure to air can alter the pH level. Acidic springs may become more neutral.
Water Addition/Heating: Adding water or heating can change the pH level.
Over Time: Even with continuous flow, the pH level can change over time in the bath.
The most accurate pH measurement is taken at the source. In the bath, it may vary slightly.
pH Levels and "Totonou"
If you've experienced "totonou" in a sauna, you'll be sensitive to hot spring pH levels too.
Entering a strongly acidic spring gives a tightening sensation on the skin, while a strongly alkaline spring makes the skin feel softer.
Sensing these pH differences is part of the enjoyment of hot springs.
Enjoying Extreme pH Hot Springs
Experiencing both Tamagawa Onsen with a pH of 1.2 and Hakuba Happo Onsen with a pH of 11.5 allows you to appreciate the vastness of Japanese hot springs.
Strongly acidic and strongly alkaline. Completely opposite pH levels. Completely different skin sensations. Experiencing these extremes lets you feel the "diversity of Japanese hot springs."
Conclusion
The pH levels of hot springs range from acidic to alkaline, offering incredible diversity. Japan boasts the world's most acidic hot spring and the country's most alkaline hot spring.
pH levels significantly affect the skin. Acidity provides a tingling sensation, while alkalinity offers a slippery softness.
By understanding pH levels, you can choose the right hot spring for you. Check the hot spring analysis report for pH levels and enjoy the diversity of Japanese hot springs through their pH levels.
