A hot (74.8 °C) sulfur-bearing sodium chloride/bicarbonate/sulfate spring — one of Japan's hotter natural sources. The water emerges clear at the wellhead with the unmistakable rotten-egg note of H₂S, neutral pH, and moderately mineralized at 1,349 mg/kg. Unusually high metasilicic acid (272.6 mg/kg) leaves the kind of silica film that makes skin feel noticeably smoother afterwards — a layered Kyushu-style soak.
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, netto 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
- Active stage of any illness (especially with fever)
- Active tuberculosis, advanced malignant tumor, severe anemia or other marked physical weakness
- Severe heart or lung disease causing shortness of breath on slight exertion
- Severe kidney disease with edema
- Gastrointestinal bleeding, visible bleeding
- Acute exacerbation of a chronic illness
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⁺191mgP50 national74%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺21.5mgP39 national9%
- Potassiumminor; matters for drinking limitsK⁺37.4mgP81 national8%
- Magnesiummild; a laxative if you drink itMg²⁺10.5mgP63 national7%
- LithiumLi⁺0.49mgP48 national0.6%
- AmmoniumNH₄⁺0.50mgP47 national0.3%
- Manganesetrace; companion to iron springsMn²⁺0.07mgP24 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻165mgP52 national48%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻182mgP56 national27%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻127mgP59 national24%
- FluorideF⁻1.2mgP49 national0.6%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃273mgP96 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂1.6mgP15 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂201mgP88 national
- ArsenicAs0.01mgP25 national
- Mercurytoxic trace — part of the drinking-safety checkHg0.0005mgP51 national
Measured at the source
On the certificate
- Chronic pain and stiffness, such as muscle and joint pain
- Rheumatoid arthritis, osteoarthritis
- Lower back pain, neuralgia, frozen shoulder, bruises, sprains and similar movement disorders
- Reduced gastrointestinal function (heaviness, bloating)
- Impaired glucose tolerance (diabetes)
- Mild hypercholesterolemia
- Mild asthma or emphysema
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