A gentle simple thermal water from the Yugashima valley in Izu. Lightly mineralized at just 189 mg/kg total dissolved solids — a mild, weakly alkaline character that sits soft on the skin rather than asserting itself. The kind of unobtrusive, easy-soaking water that rewards a long bath.
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
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.
- Aluminumshows up in acidic volcanic waterAl³⁺< —mg
- Iron (III)Fe³⁺< —mg
- Manganesetrace; companion to iron springsMn²⁺< —mg
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻52.3mgP40 national48%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻59.4mgP32 national43%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻5.3mgP8 national7%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻1.2mgP21 national2%
- Iodideyellows in air; helps blood lipidsI⁻0.08mgP30 national
- HydroxideOH⁻0.03mgP29 national
- Bromidetrace, sea-originBr⁻< —mg
- Thiosulfateoxidized sulfurS₂O₃²⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃22.4mgP7 national
- Metaarsenious acidHAsO₂0.02mgP34 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂< —mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂< —mg
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S< —mg
- CopperCu< —mg
Measured at the source
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.