A strongly alkaline simple sulfur spring (42.4 °C). At pH 9.9 at the wellhead it sits in the rare 'strongly alkaline' tier and gives that pronounced slippery feel on the skin Japanese bathers call beauty-water. The water carries the unmistakable rotten-egg note of H₂S (4.2 mg/kg HS⁻), yet total dissolved solids are only 131 mg/kg, so the body remains light and gentle. A faint fizz is even visible at the source.
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⁺42.2mgP10 national95%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺1.5mgP5 national4%
- AluminumAl³⁺0.20mgP64 national0.9%
- PotassiumK⁺0.70mgP9 national0.8%
- LithiumLi⁺0.02mgP13 national0.2%
- BariumBa²⁺0.20mgP74 national0.1%
- ManganeseMn²⁺0.20mgP45 national0.0%
- Iron (II)Fe²⁺0.0000mg0.0%
- StrontiumSr²⁺0.0000mg0.0%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻38.8mgP87 national42%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻27.0mgP16 national15%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻6.3mgP9 national9%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻6.8mgP17 national7%
- Hydrogen sulfidesulfur character — antibacterialHS⁻4.2mgP88 national6%
- HydroxideOH⁻1.6mgP92 national4%
- FluorideF⁻0.04mgP4 national0.2%
- 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.
- 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