A sodium-led bicarbonate spring, posted under its older classification name meaning "soda water containing common salt" — juso-sen in the traditional vocabulary. The bicarbonate gives the soft, smooth feel that places it in Japan's beauty-water family, while chloride, running to a little over 40 percent of the anion balance, adds a salty edge that helps warmth linger on the skin. Moderately mineralized rather than sharp, and the posted indications track the chemistry: chronic skin conditions, wounds and burns, alongside neuralgia and chronic rheumatoid arthritis.
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
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.
- All acute illnesses, especially febrile conditions
- Progressive tuberculosis
- Malignant tumor
- Severe heart disease
- Bleeding disorders
- Severe anemia
- Other illnesses in an active or progressing stage
- Early and late pregnancy (dropped from the official list in 2014)
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⁺—mg86%
- Potassiumminor; matters for drinking limitsK⁺39.1mgP81 national6%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺19.2mgP38 national6%
- Magnesiummild; a laxative if you drink itMg²⁺5.1mgP51 national3%
- AmmoniumNH₄⁺0.22mgP32 national0.1%
- Iron (II)Fe²⁺0.24mgP39 national0.1%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻573mgP80 national56%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻252mgP61 national42%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻9.1mgP19 national1%
- CarbonateCO₃²⁻2.1mgP22 national0.4%
- HSiO3HSiO₃⁻2.2mgP56 national0.2%
- Hydrogen phosphateHPO₄²⁻0.59mgP70 national0.1%
- BO2BO₂⁻0.32mgP44 national0.0%
- H2PO4H₂PO₄⁻0.05mgP26 national0.0%
- HydroxideOH⁻0.01mgP25 national0.0%
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.
- Hysteria and neurasthenia, especially in those prone to cranial congestion
- Wounds
- Burns (dropped from the official list in 2014)
- Chronic skin conditions (dropped from the official list in 2014)
- Chronic gynecological conditions (chronic cystitis, chronic adnexitis)
- Chronic rheumatoid arthritis
- Neuralgia
- Neuritis
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.
- 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.