A cold-mineral source (19.6 °C) heated for bathing, classified as a strongly alkaline simple thermal water. Lightly mineralized at just 0.326 g/kg dissolved solids, it is mild on the body, while the pH 9.5 strong alkalinity delivers the slippery, beauty-water feel on the skin that this style is known for.
Good for
Smooth skin
Bicarbonate and alkalinity gently lift dead keratin while silica hydrates, leaving skin smooth. This is the basis of the beautifying-water (bijin-no-yu 美人の湯) reputation.
dry, rough skin
Recovery
Warmth and buoyancy lower stress markers and improve sleep; habitual bathing is linked to lower rates of depression.
fatigue, stress
Take care
- Acute illness
- 活動性結核
- Malignant tumor
- 重い心臓病
- 呼吸不全
- Renal failure
- Bleeding disorders
- その他一般に病勢進行中の疾患
- 妊娠中(とくに初期と末期)
Full composition
The bar is each ion's share of charge (mval%) within its group; over 20% names the spring. Gases, silica and trace metals are measured by mass only.
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺87.7mgP26 national
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺6.4mgP20 national
- Potassiumminor; matters for drinking limitsK⁺1.0mgP14 national
- StrontiumSr²⁺0.60mgP72 national
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻111mgP44 national
- Carbonatestrongly alkaline; slippery feelCO₃²⁻51.2mgP92 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻13.0mgP15 national
- Hydrogen sulfidesulfur character — antibacterialHS⁻9.1mgP94 national
- Fluoridetrace; drinking limits applyF⁻1.4mgP53 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃28.8mgP11 national
Measured at the source
Evidence
- Maeda M. 温泉の医学的効果とその科学的根拠. J. Hot Spring Science 70:197–207, 2021.
- Naito Y et al. A Hot-Spring Water Improves Inflammatory Conditions in an Atopic Dermatitis Model. Biomedicines 13(11):2707, 2025.
- Li H et al. Bicarbonate Ionized Water Bathing Enhances Natural Killer Cell Activity. Scientific Reports 14:51851, 2024.
- Takeda M et al. Hot spring bathing practices have a positive effect on mental health in Japan. Heliyon 9(9):e19631, 2023.