A sodium-led bicarbonate spring of the classic jūsō-sen style, neutral pH and soft on the skin — squarely in Japan's beauty-water family. The 46 °C source carries a generous 99 mg/kg of metasilicic acid, which leaves the kind of fine silica film that makes skin feel noticeably smoother afterwards. A faint hydrogen sulfide note drifts off the wellhead.
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⁺241mgP58 national59%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺42.3mgP54 national12%
- PotassiumK⁺6.4mgP37 national0.9%
- FeTotalFe1.5mgP74 national0.3%
- LithiumLi⁺0.30mgP41 national0.2%
- StrontiumSr²⁺0.90mgP79 national0.1%
- BariumBa²⁺0.30mgP75 national0.0%
- ManganeseMn²⁺0.20mgP46 national0.0%
- Aluminumshows up in acidic volcanic waterAl³⁺0.0000mg
- Hydrogenmakes the water acidic — sharp and bactericidalH⁺0.0000mg
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻935mgP89 national84%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻100mgP40 national15%
- FluorideF⁻1.0mgP46 national0.3%
- BromideBr⁻0.50mgP48 national0.0%
- CarbonateCO₃²⁻0.20mgP12 national0.0%
- IodideI⁻0.20mgP51 national0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃99.3mgP54 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂13.0mgP63 national
- Metaarsenious acidHAsO₂0.0000mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂105mgP80 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.0000mg
- ArsenicAs< —mg
- CopperCu< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —mg
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.