A sodium-led bicarbonate-chloride spring — the classic juso-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, netto 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
The analysis date is not recorded on our copy of the certificate.
This list uses the wording the Ministry of the Environment replaced in 2014, so it may not match a current certificate. Items marked † were removed from the official list of contraindications then, or include a condition that was. If you have a health condition, ask a doctor before bathing.
- 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) (dropped from the official list in 2014)
- 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
The analysis date is not recorded on our copy of the certificate.
This list uses the wording the Ministry of the Environment replaced in 2014, so it may not match a current certificate. Items marked † were dropped from the official list then.
- hemorrhoids
- chronic skin conditions (dropped from the official list in 2014)
- chronic gynecological conditions (dropped from the official list in 2014)
- 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.