Myoban Yamanoyu is a simple thermal spring, with 284 mg/kg of dissolved solids and a neutral pH that keeps it gentle rather than assertive. The water is more characterful than that classification suggests: at the wellhead it runs weakly milky and clouded, carrying a very faint hydrogen sulfide note and a salty edge on the tongue. At 79 mg/kg of metasilicic acid it still lands in Japan's beauty-water family, leaving the thin silica film that makes skin feel smoother afterwards. The certificate documents the water for neuralgia, muscle and joint pain, frozen shoulder, cold sensitivity, and fatigue recovery.
Good for
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
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
From a certificate analyzed in 1994.
This list uses the wording the Ministry of the Environment replaced in 2014, so it may not match a current certificate.
- Acute illness (especially with fever)
- Active tuberculosis
- Malignant tumor
- Severe heart disease
- Respiratory failure
- Bleeding disorders
- Severe anemia
- Any other illness in a progressive stage
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.
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺17.5mgP36 national40%
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺18.5mgP4 national37%
- Magnesiummild; a laxative if you drink itMg²⁺4.5mgP48 national17%
- Potassiumminor; matters for drinking limitsK⁺4.3mgP32 national5%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻110mgP56 national74%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻44.4mgP28 national23%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻2.6mgP3 national2%
- FluorideF⁻0.30mgP22 national0.6%
- BromideBr⁻0.30mgP37 national0.0%
- H2PO4H₂PO₄⁻0.20mgP53 national0.0%
- CarbonateCO₃²⁻0.0000mg0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃79.0mgP47 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂2.1mgP19 national
- H2SO4FreeH2SO4Free0.0000mg
- Phosphoric acidH₃PO₄0.0000mg
- Metaarsenious acidHAsO₂0.0000mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂29.9mgP59 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.0000mg
Measured at the source
On the certificate
From a certificate analyzed in 1994.
This list uses the wording the Ministry of the Environment replaced in 2014, so it may not match a current certificate.
- Motor paralysis
- Chronic digestive disorders
- Hemorrhoids
- Cold sensitivity
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.
- 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.