A blend of five Umegashima wells, classified as a simple sulfur spring. At pH 9.4 it sits in the alkaline 'beauty-water' band — water that feels slippery on the skin. Mineralization is light (314 mg/kg total), but with 8.9 mg/kg HS⁻ plus thiosulfate and a trace of free H₂S the bath still carries the unmistakable sulfur-spring character: a microgreen-yellow tint and a faint rotten-egg note. A respectable 65.4 mg/kg of metasilicic acid leaves the skin noticeably smooth afterwards.
Good for
Skin conditions
Sulfur and acidic waters are antibacterial and keratolytic, studied for atopic dermatitis and psoriasis.
atopic skin, eczema
Circulation
Skin-absorbed CO₂ and hydrogen sulfide relax the vessel walls; carbon-dioxide springs can raise peripheral blood flow several-fold.
tired legs
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
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
Sensitive-skin caution
Strongly acidic or sulfur-rich water can sting broken, atopic-flare, or dry elderly skin. Ease in slowly and rinse off if it stings.
broken or dry skin
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⁺69.8mgP21 national95%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺2.4mgP9 national4%
- PotassiumK⁺1.0mgP14 national0.9%
- Magnesiummild; a laxative if you drink itMg²⁺0.09mgP7 national
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺0.07mgP18 national
- CopperCu²⁺0.05mgP89 national
- Aluminumshows up in acidic volcanic waterAl³⁺< —mg
- Iron (III)Fe³⁺< —mg
- Manganesetrace; companion to iron springsMn²⁺< —mg
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻133mgP47 national67%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻9.6mgP50 national10%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻14.4mgP27 national9%
- Hydrogen sulfidesulfur character — antibacterialHS⁻8.9mgP94 national8%
- Thiosulfateoxidized sulfurS₂O₃²⁻3.8mgP92 national2%
- BO2BO₂⁻3.1mgP74 national2%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻1.4mgP2 national1%
- HydroxideOH⁻0.40mgP76 national0.6%
- IodideI⁻0.20mgP52 national0.0%
- Hydrogen phosphateHPO₄²⁻0.10mgP34 national0.0%
- Bromidetrace, sea-originBr⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃65.4mgP41 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S< —mg
- ArsenicAs< —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.
- Tei C, Kihara T. Waon Therapy for Chronic Heart Failure. J. Cardiology 53(2):214–218, 2009.
- Coavoy-Sánchez SA et al. Hydrogen sulfide and dermatological diseases. Int. J. Dermatology, 2019.
- Naito Y et al. A Hot-Spring Water Improves Inflammatory Conditions in an Atopic Dermatitis Model. Biomedicines 13(11):2707, 2025.
- Akiyama H et al. Antimicrobial effects of acidic hot-spring water on S. aureus. J. Dermatological Science 24(3):193–200, 2000.
- Toriyama T et al. Carbon dioxide foot bathing on critical limb ischemia. International Angiology 21(4):367–373, 2002.
- 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.
- Ministry of the Environment, Japan. 禁忌症及び入浴又は飲用上の注意事項 (2014 notice).official