A blend of five wellheads (Shin'yu Springs #1, #2, #3, #5 and #7) classified as a simple sulfur spring of the hydrogen sulfide subtype. Emerges hot at 60.5 °C, milky-white at the source with the unmistakable rotten-egg note of H₂S and a faint astringent bite on the tongue. Weakly acidic at pH 5.1 and only lightly mineralized (345 mg/kg total dissolved solids), it nonetheless carries a generous 82 mg/kg of free hydrogen sulfide alongside 193 mg/kg of free CO₂ — the kind of dense sulfur water long credited with helping stubborn skin conditions.
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⁺—mg48%
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺2.9mgP1 national25%
- Magnesiummild; a laxative if you drink itMg²⁺—mg23%
- Potassiumminor; matters for drinking limitsK⁺—mg4%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻28.0mgP16 national46%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻—mg31%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻2.2mgP3 national11%
- Thiosulfateoxidized sulfurS₂O₃²⁻1.7mgP80 national6%
- Hydrogen sulfidesulfur character — antibacterialHS⁻—mg6%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃31.5mgP14 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂193mgP88 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S82.0mgP100 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