A hot (67.4 °C) sodium-calcium chloride spring from the Shima Onsen area, with sulfate adding quiet body to the salty chloride core. Neutral pH and 1,830 mg/kg of dissolved solids give long-lasting, heat-retaining warmth. Metasilicic acid at 126 mg/kg leaves a thin silica film that smooths the skin afterwards.
Good for
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
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
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
- 急性疾患(特に熱のある場合)
- Active tuberculosis
- Malignant tumor
- 重い心臓病
- 呼吸不全
- Renal failure
- Bleeding disorders
- Severe anemia
- その他一般に病勢進行中の疾患
- 群馬県の定めによる
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⁺410mgP69 national67%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺144mgP79 national27%
- Potassiumminor; matters for drinking limitsK⁺49.1mgP84 national5%
- MagnesiumMg²⁺1.2mgP28 national0.4%
- Manganesetrace; companion to iron springsMn²⁺0.06mgP25 national
- Aluminumshows up in acidic volcanic waterAl³⁺0.05mgP30 national
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺0.05mgP17 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻624mgP76 national66%
- FluorideF⁻0.70mgP41 national0.2%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻388mgP82 national
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻35.0mgP20 national
- Iodideyellows in air; helps blood lipidsI⁻3.4mgP90 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃126mgP66 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂—mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂22.0mgP54 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂SNDmg
Measured at the source
On the certificate
- Chronic digestive disorders
- 慢性皮膚病
- 群馬県の定めによる
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.