A sodium-led bicarbonate-chloride spring — the classic jūsō-sen style softened with a salty edge from a chloride sub-type. Weakly alkaline and gentle on the skin, it sits squarely in Japan's beauty-water family. The wellhead runs at 81.6 °C, among the country's hottest natural sources, and a generous 170 mg/kg of metasilicic acid leaves skin feeling noticeably 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
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⁺511mgP76 national94%
- Potassiumminor; matters for drinking limitsK⁺27.3mgP72 national3%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺6.7mgP21 national
- LithiumLi⁺2.2mgP92 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻233mgP57 national28%
- Fluoridetrace; drinking limits applyF⁻0.41mgP31 national2%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻975mgP90 national
- Carbonatestrongly alkaline; slippery feelCO₃²⁻5.1mgP34 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃170mgP76 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂45.6mgP86 national
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.
- 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.