A simple sulfur spring pumped up at 92 °C, which puts it among Japan's hottest natural sources — the well sits in the Okuhida hot spring villages of Takayama. The water runs colorless and clear, yet carries the unmistakable faint rotten-egg note of hydrogen sulfide from free H₂S and hydrosulfide ions. At neutral pH and only 793 mg/kg of dissolved solids it stays lightly mineralized and gentle on the body. What stands out is the metasilicic acid at 247 mg/kg — enough to leave the kind of thin silica film that puts this water squarely in Japan's beauty-water family.
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
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
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⁺137mgP38 national77%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺24.0mgP41 national15%
- Potassiumminor; matters for drinking limitsK⁺17.0mgP56 national6%
- LithiumLi⁺1.1mgP77 national2%
- MagnesiumMg²⁺0.21mgP14 national0.3%
- ManganeseMn²⁺0.27mgP46 national0.1%
- FeTotalFe0.02mgP12 national0.0%
- AluminumAl³⁺< —mg0.0%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻145mgP49 national53%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻176mgP55 national37%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻27.0mgP35 national7%
- Hydrogen sulfidesulfur character — antibacterialHS⁻2.9mgP82 national1%
- Thiosulfateoxidized sulfurS₂O₃²⁻4.5mgP93 national1%
- CarbonateCO₃²⁻0.11mgP11 national0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃247mgP95 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂9.7mgP54 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂37.0mgP63 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S4.1mgP84 national
- ArsenicAs0.0080mgP21 national
- 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.
- 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.
- 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