A sodium-led bicarbonate-chloride spring drawn very hot (83.5 °C) from the Shirakawa well in Ureshino. Weakly alkaline (pH 8.3 at the source) and soft on the skin, it sits squarely in the Japanese 'beauty-water' family that Ureshino is famous for. With 132.7 mg/kg of metasilicic acid layered onto the bicarbonate softness, the water leaves a thin 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, netto 熱の湯).
cold sensitivity
Gut & metabolic
Bicarbonate and sulfate waters, taken as a drink, neutralize stomach acid and help with constipation and gout.
stomach, gout (drinking)
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
From a certificate analyzed in 2023.
This list uses the wording the Ministry of the Environment replaced in 2014, so it may not match a current certificate. Items marked † were removed from the official list of contraindications then, or include a condition that was. If you have a health condition, ask a doctor before bathing.
- Acute illness (especially when fever is present)
- Active tuberculosis
- Malignant tumor
- Severe heart disease
- Respiratory failure
- Bleeding disorders
- Severe anemia
- Any illness in an actively progressing stage
- Pregnancy (especially the early and late stages) (dropped from the official list in 2014)
- Kidney disease
- Hypertension
- Any other condition with edema
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⁺386mgP70 national93%
- Potassiumminor; matters for drinking limitsK⁺22.5mgP67 national3%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺8.1mgP23 national2%
- LithiumLi⁺1.0mgP74 national0.8%
- MagnesiumMg²⁺0.80mgP24 national0.4%
- AmmoniumNH₄⁺1.0mgP66 national0.3%
- Iron (II)Fe²⁺0.80mgP60 national0.2%
- StrontiumSr²⁺0.30mgP52 national0.1%
- AluminumAl³⁺0.10mgP56 national0.1%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻688mgP83 national64%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻197mgP55 national32%
- Fluoridetrace; drinking limits applyF⁻6.8mgP83 national2%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻7.0mgP39 national1%
- SulfateSO₄²⁻6.3mgP17 national0.7%
- BromideBr⁻0.50mgP48 national0.1%
- Hydrogen phosphateHPO₄²⁻0.20mgP52 national
- Hydrogen sulfidesulfur character — antibacterialHS⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃133mgP65 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂33.5mgP81 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂< —mg
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S< —mg
- ArsenicAs0.0040mgP12 national
- CadmiumCd< —mg
- CopperCu< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —mg
- Radonfaint radon — studied for joint pain (hormesis)RnNDmg
Measured at the source
On the certificate
From a certificate analyzed in 2023.
This list uses the wording the Ministry of the Environment replaced in 2014, so it may not match a current certificate. Items marked † were dropped from the official list then.
- Hemorrhoids
- Cold sensitivity
- Chronic skin conditions (dropped from the official list in 2014)
- Chronic gynecological conditions (dropped from the official list in 2014)
- Chronic eczema
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.
- Matsumoto S et al. Hot spring bathing and HbA1c in type 2 diabetes. J. JAPMC 73(3):163–170, 2010.
- Takeda M et al. Hot spring bathing practices have a positive effect on mental health in Japan. Heliyon 9(9):e19631, 2023.