A sodium-led bicarbonate spring — the classic jūsō-sen (soda-water) style, weakly alkaline and soft on the skin, placing it in Japan's beauty-water family. The source emerges hot at over 51 °C; the water is medium yellow-brown and clear with a moderate mineral note. A generous 198 mg/kg of metasilicic acid leaves the kind of silica film that makes skin feel noticeably smoother afterwards.
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
Aches & joints
Warmth eases stiffness and raises the pain threshold. Radon and sulfate springs show the strongest evidence for joint and muscle pain.
stiff shoulders
Recovery
Warmth and buoyancy lower stress markers and improve sleep; habitual bathing is linked to lower rates of depression.
fatigue, stress
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⁺287mgP60 national91%
- LithiumLi⁺0.10mgP29 national0.1%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺35.0mgP49 national
- AmmoniumNH₄⁺1.6mgP76 national
- Fluoridetrace; drinking limits applyF⁻5.8mgP81 national2%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻55.2mgP93 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃198mgP85 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂3.3mgP26 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.
- Donaubauer AJ et al. Serial radon spa therapy on pain in musculoskeletal disorders. Frontiers in Immunology, 2024.
- Verhagen AP et al. Balneotherapy for rheumatoid arthritis. Cochrane Database of Systematic Reviews CD000518, 2015.
- 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.