A sodium-led bicarbonate spring with a sulfur edge — classic 'jūsō-sen' soda-water territory layered with the unmistakable rotten-egg note of H₂S. The wellhead runs hot at 83.5 °C, among Japan's hottest natural sources, and still reaches the bath at 71.8 °C. Weakly alkaline (pH 8.2) and lightly mineralized, it sits in the Japanese 'beauty-water' family — soft on the skin despite the heat. Diluted with fresh water at the bath but otherwise served as flowing source water.
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
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
- 病気の活動期（特に熱のあるとき）、活動性の結核、進行した悪性腫瘍または高度の貧血など身体衰弱の著しい場合
- 少し動くと息切れがするような重い心臓または肺の病気、むくみのあるような腎臓の病気
- 消化管出血、目に見えている出血や近い時期に出血の可能性のある場合
- 慢性の病気の活動期
- 皮膚または粘膜の過敏な人、高齢者の皮膚乾燥症
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⁺241mgP56 national93%
- AmmoniumNH₄⁺11.8mgP96 national6%
- LithiumLi⁺0.50mgP55 national0.6%
- CalciumCa²⁺1.0mgP2 national0.5%
- Aluminumshows up in acidic volcanic waterAl³⁺< —mg
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺< —mg
- Magnesiummild; a laxative if you drink itMg²⁺< —mg
- Manganesetrace; companion to iron springsMn²⁺< —mg
- StrontiumSr²⁺< —mg
- ZincZn²⁺< —mg
- Hydrogen sulfidesulfur character — antibacterialHS⁻1.5mgP74 national5%
- FluorideF⁻1.3mgP50 national0.7%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻588mgP79 national
- Bromidetrace, sea-originBr⁻< —mg
- Iodideyellows in air; helps blood lipidsI⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃109mgP58 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂5.7mgP40 national
Measured at the source
On the certificate
- きりきず、末梢循環障害、冷え性、皮膚乾燥症、アトピー性皮膚炎、尋常性乾癬、慢性湿疹、表皮化膿症
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.
- 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