A calcium- and sodium-led sulfate–chloride spring emerging at 45.4 °C, weakly alkaline and hypotonic. Sulfate dominates the anion balance (about 90 mval%) with chloride underneath, giving the water a settled, mineral-rich body rather than a salty bite. The posted indications include cuts, peripheral circulation issues, sensitivity to cold and dry skin.
Good for
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
Circulation
Skin-absorbed CO₂ and hydrogen sulfide relax the vessel walls; carbon-dioxide springs can raise peripheral blood flow several-fold.
tired legs
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
- 一般的禁忌症: 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身体衰弱の著しい場合、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
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⁺174mgP82 national59%
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺136mgP34 national40%
- PotassiumK⁺5.4mgP36 national0.9%
- MagnesiumMg²⁺0.70mgP23 national0.4%
- StrontiumSr²⁺0.60mgP69 national0.1%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻634mgP92 national90%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻27.7mgP21 national5%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻43.4mgP25 national5%
- FluorideF⁻0.40mgP33 national0.1%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃40.0mgP23 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂0.80mgP11 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂4.4mgP27 national
- ArsenicAs0.02mgP36 national
- CadmiumCd< —mg
- CopperCu< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —mg
Measured at the source
On the certificate
- 一般的適応症: 筋肉又は関節の慢性的な痛み又はこわばり(関節リウマチ、変形性関節症、腰痛症、神経痛、五十肩、打撲、捻挫などの慢性期)、運動麻痺による筋肉のこわばり、胃腸機能の低下(胃がもたれる感じ、ガスがたまる感じ)、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、疲労回復、健康増進
- 泉質別適応症: きりきず、末梢循環障害、冷え性、うつ状態、皮膚乾燥症
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.
- 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.