A cold-mineral spring (14.3 °C) at Ihatasan Yakushiji, reheated for bathing. Lightly mineralized at about 697 mg/kg, it is alkaline and soft on the skin, with notable fluoride and metasilicic acid carried alongside the bicarbonate framework. The certificate also approves it for drinking — one of the rarer sources that doubles as a fountain — and lists digestive complaints among its indications.
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
Recovery
Warmth and buoyancy lower stress markers and improve sleep; habitual bathing is linked to lower rates of depression.
fatigue, stress
Take care
- 病気の活動期(特に熱のある時)
- Active tuberculosis
- 進行した悪性腫瘍又は高度の貧血など身体衰弱の著しい場合
- 少し動くと息切れし、又は動悸のするような重い心臓又は肺の病気
- むくみのあるような重い腎臓の病気
- 消化管出血
- 目に見える出血があるとき
- 慢性の病気の悪化期
- 下痢のとき
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⁺212mgP50 national98%
- CalciumCa²⁺1.2mgP4 national0.6%
- PotassiumK⁺1.4mgP16 national0.4%
- LithiumLi⁺0.20mgP37 national0.3%
- MagnesiumMg²⁺0.20mgP15 national0.2%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻367mgP67 national68%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻75.0mgP97 national28%
- Fluoridetrace; drinking limits applyF⁻4.5mgP78 national3%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻8.3mgP12 national3%
- SulfateSO₄²⁻1.9mgP12 national0.4%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃20.0mgP6 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂9.0mgP48 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂13.2mgP44 national
- ArsenicAs< —mg
- CadmiumCd< —mg
- ChromiumCr< —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.
- Naito Y et al. A Hot-Spring Water Improves Inflammatory Conditions in an Atopic Dermatitis Model. Biomedicines 13(11):2707, 2025.
- 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.