A simple thermal spring from the Yagurumaso No. 2 well at Harazuru. Hot at 46.6 °C and weakly alkaline, it is soft on the skin in the Japanese beauty-water family, carrying a faint hydrogen sulfide note at the source. With 69 mg/kg of metasilicic acid, it is a gentle, lightly mineralized water that leaves skin feeling smooth.
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
- acute phase of any illness (especially with fever)
- active tuberculosis
- severe heart or lung disease
- severe kidney disease
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⁺186mgP45 national91%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺10.2mgP27 national6%
- Magnesiummild; a laxative if you drink itMg²⁺2.6mgP38 national2%
- Potassiumminor; matters for drinking limitsK⁺4.2mgP32 national1%
- LithiumLi⁺0.10mgP27 national0.1%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻275mgP61 national50%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻131mgP46 national41%
- Fluoridetrace; drinking limits applyF⁻14.6mgP97 national9%
- SulfateSO₄²⁻1.1mgP9 national0.3%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃69.2mgP45 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂18.0mgP72 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.20mgP65 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂0.0000mg
- ArsenicAs0.0030mgP12 national
- CadmiumCd< —mg
- ChromiumCr< —mg
- CopperCu< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —mg
Measured at the source
On the certificate
- chronic muscle or joint pain and stiffness
- poor circulation (sensitivity to cold)
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.