A sodium-led bicarbonate-chloride spring — the classic 'jūsō-sen' style softened by a faint salt-tinged finish. Weakly alkaline (pH 8.17) and soft on the skin, it sits squarely in the Japanese "beauty-water" family that Ureshino is best known for. The wellhead runs hot at 87.9 °C — among Japan's hottest natural sources — and a generous 161 mg/kg of metasilicic acid leaves the kind of silica film that makes skin feel noticeably smoother afterwards.
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⁺453mgP74 national
- Potassiumminor; matters for drinking limitsK⁺28.6mgP73 national
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺6.0mgP19 national
- LithiumLi⁺1.2mgP79 national
- AmmoniumNH₄⁺0.90mgP64 national
- Magnesiummild; a laxative if you drink itMg²⁺0.70mgP23 national
- StrontiumSr²⁺0.40mgP62 national
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻930mgP88 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻252mgP59 national
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻8.4mgP20 national
- Fluoridetrace; drinking limits applyF⁻7.8mgP86 national
- Thiosulfateoxidized sulfurS₂O₃²⁻0.20mgP55 national
- Iodideyellows in air; helps blood lipidsI⁻0.10mgP37 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃161mgP74 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂42.4mgP86 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂2.8mgP24 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.