湯Simple
A gentle, lightly mineralized alkaline hypotonic spring that qualifies as an onsen under Japan's Hot Spring Act on the strength of its total sulfur, fluoride, and metaboric acid content rather than any single dominant ion type. Because the source emerges below 25 °C as a cold-mineral spring, it is reheated year-round to a comfortable 40–42 °C for bathing. The certificate notes the water is not suitable for drinking.
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
Contraindications
- acute illness (especially when accompanied by fever)
- active tuberculosis
- malignant tumors
- severe heart disease
- respiratory failure
- renal failure
- hemorrhagic disorders
- severe anemia
- any other disease in an actively progressing state
- pregnancy (especially the early and late stages)
Measured at the source
Tonicity
Hypotonic
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.