A sodium-led bicarbonate spring with a salt-tinged finish from a chloride sub-type — the classic jūsō-sen style and a very hot source at 81.6 °C, placing it among Japan's hottest natural sources. Weakly alkaline and soft on the skin, it sits in Japan's beauty-water family, carrying a very faint hydrogen sulfide note. It holds metasilicic acid for a smoother-skin film, plus enough radon (about 34 Bq/kg) to fall in the hormesis tradition.
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
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⁺446mgP73 national94%
- Potassiumminor; matters for drinking limitsK⁺25.1mgP70 national3%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺6.9mgP21 national2%
- LithiumLi⁺1.0mgP74 national0.7%
- MagnesiumMg²⁺0.90mgP25 national0.4%
- AmmoniumNH₄⁺1.1mgP67 national0.3%
- StrontiumSr²⁺0.30mgP55 national0.0%
- Iron (II)Fe²⁺0.10mgP30 national0.0%
- ZincZn²⁺< —mg
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻852mgP87 national70%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻201mgP54 national28%
- Fluoridetrace; drinking limits applyF⁻5.4mgP79 national1%
- SulfateSO₄²⁻7.8mgP19 national0.8%
- BromideBr⁻0.60mgP49 national0.0%
- Hydrogen sulfideHS⁻0.20mgP40 national0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃72.4mgP45 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂41.8mgP85 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂35.2mgP63 national
- ArsenicAs0.01mgP24 national
- CopperCu< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —mg
Measured at the source
On the certificate
- Chronic pain or stiffness of muscles or joints (rheumatoid arthritis, osteoarthritis, lower back pain, neuralgia, frozen shoulder, bruises, sprains)
- Peripheral circulatory disorders
- Reduced gastrointestinal function (heaviness in the stomach, intestinal gas buildup)
- Mild hypertension
- Impaired glucose tolerance (diabetes)
- Mild hypercholesterolemia
- Mild asthma or emphysema
- Hemorrhoids
- Stress-related symptoms (sleep disorders, depressive states)
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.
- Naito Y et al. A Hot-Spring Water Improves Inflammatory Conditions in an Atopic Dermatitis Model. Biomedicines 13(11):2707, 2025.
- 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.