A sodium-led bicarbonate spring — the classic jūsō-sen style — with chloride and sulfate nuances layered in, emerging hot at the source. Weakly alkaline and soft on the skin, it sits in the Japanese beauty-water family. At the wellhead the water carries a faint yellow-brown tint with a weak salty tang and a metallic iron note. A fair 88.4 mg/kg of metasilicic acid leaves the kind of silica film that makes skin feel smoother.
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
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, 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⁺593mgP77 national86%
- Magnesiummild; a laxative if you drink itMg²⁺18.2mgP71 national5%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺28.8mgP47 national5%
- Potassiumminor; matters for drinking limitsK⁺28.2mgP72 national2%
- LithiumLi⁺1.9mgP91 national0.9%
- AmmoniumNH₄⁺3.7mgP86 national0.7%
- StrontiumSr²⁺1.4mgP80 national0.1%
- Iron (II)Fe²⁺0.30mgP45 national0.1%
- AluminumAl³⁺0.10mgP57 national0.0%
- BariumBa²⁺0.10mgP54 national0.0%
- HydrogenH⁺0.0000mg0.0%
- ManganeseMn²⁺0.0000mg0.0%
- ZincZn²⁺0.0000mg0.0%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻1,370mgP93 national75%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻216mgP70 national15%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻110mgP43 national10%
- FluorideF⁻0.90mgP46 national0.2%
- BromideBr⁻0.40mgP41 national0.0%
- IodideI⁻0.30mgP61 national0.0%
- Hydrogen phosphateHPO₄²⁻0.10mgP39 national0.0%
- AsO2AsO₂⁻0.0000mg0.0%
- BO2BO₂⁻0.0000mg0.0%
- CarbonateCO₃²⁻0.0000mg0.0%
- Hydrogen sulfideHS⁻0.0000mg0.0%
- HSiO3HSiO₃⁻0.0000mg0.0%
- ThiosulfateS₂O₃²⁻0.0000mg0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃88.4mgP52 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂45.4mgP85 national
- Metaarsenious acidHAsO₂0.0000mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂141mgP85 national
- 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.
- 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.
- 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.