A hot (72.9 °C), weakly acidic simple-sulfur spring of the hydrogen sulfide sub-type. Lightly mineralized at 0.199 g/kg of dissolved solids, but with 4.0 mg/kg of free H₂S it carries the unmistakable rotten-egg note that defines a sulfur bath. The water is gentle in body yet distinctly sulfurous — characteristic of the Hachimantai highlands above Amihari.
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
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
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.
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺15.0mgP32 national58%
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺4.6mgP1 national15%
- Magnesiummild; a laxative if you drink itMg²⁺2.0mgP35 national12%
- Aluminumshows up in acidic volcanic waterAl³⁺1.3mgP79 national11%
- Potassiumminor; matters for drinking limitsK⁺0.80mgP11 national2%
- FeTotalFe0.50mgP56 national2%
- ManganeseMn²⁺0.0000mg0.0%
- LithiumLi⁺< —mg0.0%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻75.0mgP50 national74%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻29.0mgP17 national23%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻2.1mgP3 national3%
- FluorideF⁻0.20mgP17 national0.5%
- ThiosulfateS₂O₃²⁻0.0000mg0.0%
- Bromidetrace, sea-originBr⁻< —mg
- Hydrogen sulfidesulfur character — antibacterialHS⁻< —mg
- Iodideyellows in air; helps blood lipidsI⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃68.0mgP43 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂0.20mgP6 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂29.0mgP59 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S4.0mgP84 national
- ArsenicAs0.0020mgP8 national
- Mercurytoxic trace — part of the drinking-safety checkHg0.0007mgP53 national
- CadmiumCd< —mg
- CopperCu< —mg
- LeadPb< —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.
- 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.
- 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