A sodium chloride spring carrying dissolved sulfur — classed as a sulfur-bearing sodium-chloride water. At pH 9.1 it is alkaline with the slippery beauty-water feel on the skin, and the dissolved hydrogen sulfide gives it a sulfurous taste and the characteristic rotten-egg note. A hot source (47.8 °C) of moderate mineralization (about 3,900 mg/kg dissolved solids) with noticeable body.
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
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, netto 熱の湯).
cold sensitivity
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⁺1,367mgP90 national96%
- Magnesiummild; a laxative if you drink itMg²⁺16.5mgP69 national1%
- LithiumLi⁺6.3mgP96 national1%
- AmmoniumNH₄⁺18.1mgP97 national0.7%
- StrontiumSr²⁺2.9mgP88 national0.2%
- BariumBa²⁺1.4mgP92 national0.0%
- CalciumCa²⁺0.30mgP1 national0.0%
- Hydrogenmakes the water acidic — sharp and bactericidalH⁺0.0000mg
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻1,812mgP87 national79%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻124mgP99 national6%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻235mgP60 national6%
- Hydrogen phosphateHPO₄²⁻145mgP99 national5%
- Fluoridetrace; drinking limits applyF⁻27.8mgP99 national2%
- Hydrogen sulfidesulfur character — antibacterialHS⁻24.3mgP98 national1%
- BromideBr⁻4.3mgP80 national0.1%
- HydroxideOH⁻0.30mgP74 national0.0%
- IodideI⁻0.30mgP61 national0.0%
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂85.8mgP96 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃33.1mgP15 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.20mgP65 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂0.0000mg
- Mercurytoxic trace — part of the drinking-safety checkHg0.0009mgP60 national
- ArsenicAs< —mg
- CadmiumCd< —mg
- ChromiumCr< —mg
- CopperCu< —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.
- 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