A sodium-led bicarbonate spring with a chloride sub-type layered in — the classic jūsō-sen style, served hot at 57.4 °C from the wellhead. Weakly alkaline and soft on the skin, it sits squarely in Japan's beauty-water family. A generous 177 mg/kg of metasilicic acid leaves the kind of silica film that makes skin feel noticeably smoother, while a faint metallic taste and odor betray the trace iron carried up from depth.
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
Warming
Salt forms a film on the skin that slows heat loss, so the warmth lingers long after the bath (the classic heat-keeping water, nettō 熱の湯).
cold sensitivity
Cuts
Mineral-rich chloride, sulfate and sulfur waters have a long-recorded soothing effect on minor cuts and slow-healing skin.
minor wounds
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⁺254mgP57 national74%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺32.4mgP48 national11%
- Magnesiummild; a laxative if you drink itMg²⁺15.3mgP67 national8%
- Potassiumminor; matters for drinking limitsK⁺30.2mgP74 national5%
- LithiumLi⁺1.3mgP85 national1%
- Iron (II)Fe²⁺0.40mgP48 national0.1%
- StrontiumSr²⁺0.30mgP55 national0.1%
- BariumBa²⁺0.20mgP74 national0.0%
- ZincZn²⁺< —mg
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻568mgP79 national66%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻119mgP44 national24%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻72.2mgP48 national11%
- FluorideF⁻0.20mgP17 national0.1%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃177mgP78 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂6.4mgP44 national
- Metaarsenious acidHAsO₂0.0000mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂4.4mgP29 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S< —mg
- CadmiumCd< —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.
- Kario K et al. Hemodynamic Effects of Hot Spring Bathing. Hypertension Research 46(3):711–720, 2023.
- 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.