An alkaline simple sulfur spring with a strongly alkaline pH of 9.6 that gives a remarkable slippery, beauty-water feel on the skin. It carries hydrogen sulfide, so the pale-yellow water at the source has a faint metallic-and-sulfur note. Sodium and sulfate lead the modest mineralization at 663 mg/kg.
Good for
Skin conditions
Sulfur and acidic waters are antibacterial and keratolytic, studied for atopic dermatitis and psoriasis.
atopic skin, eczema
Circulation
Skin-absorbed CO₂ and hydrogen sulfide relax the vessel walls; carbon-dioxide springs can raise peripheral blood flow several-fold.
tired legs
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
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
Take care
Sensitive-skin caution
Strongly acidic or sulfur-rich water can sting broken, atopic-flare, or dry elderly skin. Ease in slowly and rinse off if it stings.
broken or dry skin
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⁺187mgP48 national87%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺22.4mgP41 national12%
- AluminumAl³⁺0.40mgP74 national0.4%
- PotassiumK⁺0.70mgP9 national0.2%
- Iron (II)Fe²⁺0.20mgP39 national0.1%
- BariumBa²⁺0.0000mg0.0%
- HydrogenH⁺0.0000mg0.0%
- LithiumLi⁺0.0000mg0.0%
- MagnesiumMg²⁺0.0000mg0.0%
- ManganeseMn²⁺0.0000mg0.0%
- AmmoniumNH₄⁺0.0000mg0.0%
- StrontiumSr²⁺0.0000mg0.0%
- ZincZn²⁺0.0000mg0.0%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻323mgP75 national70%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻68.9mgP32 national20%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻18.8mgP66 national7%
- Hydrogen sulfidesulfur character — antibacterialHS⁻3.8mgP87 national1%
- BicarbonateHCO₃⁻3.6mgP2 national0.6%
- FluorideF⁻0.60mgP38 national0.3%
- BO2BO₂⁻0.30mgP44 national0.1%
- BromideBr⁻0.30mgP36 national0.0%
- Hydrogen phosphateHPO₄²⁻0.0000mg0.0%
- IodideI⁻0.0000mg0.0%
- ThiosulfateS₂O₃²⁻0.0000mg0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃31.5mgP14 national
- H2SO4FreeH2SO4Free0.0000mg
- Phosphoric acidH₃PO₄0.0000mg
- Metaarsenious acidHAsO₂0.0000mg
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂0.0000mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂0.0000mg
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.0000mg
- ArsenicAs< —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.
- Tei C, Kihara T. Waon Therapy for Chronic Heart Failure. J. Cardiology 53(2):214–218, 2009.
- Coavoy-Sánchez SA et al. Hydrogen sulfide and dermatological diseases. Int. J. Dermatology, 2019.
- Naito Y et al. A Hot-Spring Water Improves Inflammatory Conditions in an Atopic Dermatitis Model. Biomedicines 13(11):2707, 2025.
- Akiyama H et al. Antimicrobial effects of acidic hot-spring water on S. aureus. J. Dermatological Science 24(3):193–200, 2000.
- Toriyama T et al. Carbon dioxide foot bathing on critical limb ischemia. International Angiology 21(4):367–373, 2002.
- 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.
- Ministry of the Environment, Japan. 禁忌症及び入浴又は飲用上の注意事項 (2014 notice).official