A strongly acidic calcium sulfate spring rising in the Myoban district of Beppu, recorded on the certificate under its older name as an acidic gypsum spring. At pH 2.4 the water is sharp enough to sting slightly on contact; at the wellhead it shows a faintly milky, slightly cloudy cast with a strongly sour, metallic taste and almost no smell. Sulfate gives it real body at 1,374 mg/kg of dissolved solids, while an exceptional 396 mg/kg of metasilicic acid leaves the kind of silica film that makes skin feel noticeably smoother. It emerges at 90.7 °C, placing it among Japan's hottest natural sources.
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
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
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⁺105mgP74 national34%
- Hydrogenmakes the water acidic — sharp and bactericidalH⁺4.0mgP75 national26%
- Aluminumshows up in acidic volcanic waterAl³⁺19.9mgP91 national14%
- Magnesiummild; a laxative if you drink itMg²⁺24.2mgP73 national13%
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺28.8mgP6 national8%
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺13.3mgP92 national3%
- PotassiumK⁺5.1mgP34 national0.8%
- Iron (III)Fe³⁺2.0mgP89 national0.7%
- ManganeseMn²⁺1.5mgP85 national0.3%
- AmmoniumNH₄⁺0.90mgP63 national0.3%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻678mgP92 national93%
- HSO4HSO491.0mgP66 national6%
- ChlorideCl⁻3.2mgP4 national0.6%
- FluorideF⁻0.30mgP22 national0.1%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃396mgP99 national
- H2SO4FreeH2SO4Free0.90mgP70 national
- Phosphoric acidH₃PO₄0.0000mg
- Metaarsenious acidHAsO₂0.0000mg
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂0.0000mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂66.9mgP74 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.50mgP72 national
- Mercurytoxic trace — part of the drinking-safety checkHg0.0013mgP82 national
- ArsenicAs0.0010mgP6 national
- CadmiumCd< —mg
- CopperCu< —mg
- LeadPb< —mg
Measured at the source
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