A sulfur-bearing sodium spring layering sulfate, chloride, and bicarbonate — drawn at 74.8 °C and delivered to the Kawara-no-Yu and Yumae open-air baths at 43.9 °C and 46.6 °C respectively. Near-neutral at pH 7.2, it carries a soft hydrogen-sulfide note with a salty edge from chloride and a touch of bicarbonate softness. The source sits among Japan's hotter natural wellheads, blended in a mixing tank from two parent wells.
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
Warming
Salt forms a film on the skin that slows heat loss, so the warmth lingers long after the bath (the classic heat-keeping water, nettō 熱の湯).
cold sensitivity
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
- 病気の活動期（特に熱のあるとき）、活動性の結核、進行した悪性腫瘍又は高度の貧血など全身衰弱の著しい場合
- 少し動くと息苦しくなるような重い心臓又は肺の病気、むくみのあるような重い腎臓の病気、消化管出血、目に見える出血があるとき、慢性の病気の急性増悪期
- 皮膚又は粘膜の過敏な人、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⁺668mgP80 national90%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺36.9mgP50 national
- Potassiumminor; matters for drinking limitsK⁺28.0mgP72 national
- Magnesiummild; a laxative if you drink itMg²⁺2.9mgP38 national
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺—mg
- Hydrogenmakes the water acidic — sharp and bactericidalH⁺—mg
- LithiumLi⁺—mg
- AmmoniumNH₄⁺—mg
- StrontiumSr²⁺—mg
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻765mgP78 national64%
- Bromidetrace, sea-originBr⁻1.1mgP60 national
- Carbonatestrongly alkaline; slippery feelCO₃²⁻—mg
- Fluoridetrace; drinking limits applyF⁻—mg
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻—mg
- Hydrogen sulfidesulfur character — antibacterialHS⁻—mg
- Iodideyellows in air; helps blood lipidsI⁻—mg
- Thiosulfateoxidized sulfurS₂O₃²⁻—mg
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻—mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃—mg
- 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
Measured at the source
On the certificate
- 筋肉痛、関節痛の慢性的な痛みまたはこわばり（関節リウマチ、変形性関節症、腰痛症、神経痛、五十肩、打撲、捻挫などの運動器障害）
- 冷え性、末梢循環障害
- 胃腸機能の低下（胃がもたれる、腸にガスがたまるなど）
- 軽症高血圧、耐糖能異常（糖尿病）、軽い高コレステロール血症、軽い喘息又は肺気腫
- 痔の痛み、自律神経不安定症、ストレスによる諸症状（睡眠障害、うつ状態など）
- 病後回復期、健康増進
- きりきず、末梢循環障害、冷え性、うつ状態、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.
- Kario K et al. Hemodynamic Effects of Hot Spring Bathing. Hypertension Research 46(3):711–720, 2023.
- 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