A sodium-calcium chloride spring with a moderate salty body — 3,941 mg/kg of dissolved solids, weakly alkaline and soft on the skin. The wellhead runs at only 25.5 °C, so the bath is reheated and recirculated, served around 42 °C.
Good for
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
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
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 2017.
- Active stage of any illness (especially with fever)
- Active tuberculosis
- Advanced malignant tumor, severe anemia or other marked physical weakness
- Severe heart or lung disease in which even slight physical activity causes great distress
- Renal failure with edema
- Gastrointestinal bleeding
- Visible bleeding
- Acute exacerbation of a chronic illness
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⁺1,094mgP87 national55%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺390mgP91 national
- FeTotalFe0.30mgP56 national
- Manganesetrace; companion to iron springsMn²⁺0.20mgP47 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻1,488mgP85 national
- Bromidetrace, sea-originBr⁻8.6mgP89 national
- Iodideyellows in air; helps blood lipidsI⁻0.10mgP34 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃18.7mgP4 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂0.20mgP6 national
- Metaarsenious acidHAsO₂< 0.10mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂9.9mgP40 national
- Radonfaint radon — studied for joint pain (hormesis)Rn—mg
Measured at the source
On the certificate
From a certificate analyzed in 2017.
- Chronic muscle or joint pain or stiffness
- Muscle stiffness associated with motor paralysis
- Peripheral circulation disorders
- Reduced gastrointestinal function
- Mild hypertension
- Impaired glucose tolerance (diabetes)
- Mild hypercholesterolemia
- Mild asthma or emphysema
- Hemorrhoid pain
- Peripheral circulation disorders
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.
- 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.