A sodium-led bicarbonate-chloride spring — the classic jūsō-sen style, with a salty edge layered in. Weakly alkaline and soft on the skin, it sits in the Japanese beauty-water family. The hot source (54.6 °C) is served as untreated free-flow: no dilution, heating, recirculation, or disinfection.
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, nettō 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
- acute illness (especially with fever)
- active tuberculosis
- malignant tumors
- severe heart disease
- hemorrhagic conditions
- severe anemia
- respiratory failure
- renal failure
- pregnancy (especially early and late stages)
- other generally progressing illnesses
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⁺—mg
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺—mg
- Potassiumminor; matters for drinking limitsK⁺—mg
- LithiumLi⁺—mg
- Magnesiummild; a laxative if you drink itMg²⁺—mg
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺—mg
- StrontiumSr²⁺—mg
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻—mg
- Fluoridetrace; drinking limits applyF⁻—mg
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻—mg
- Hydrogen sulfidesulfur character — antibacterialHS⁻—mg
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻—mg
Measured at the source
On the certificate
- hemorrhoids
- chronic skin conditions
- chronic gynecological conditions
- chronic cholecystitis
- gallstones
- obesity
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.