A sharp, prickly acidic spring from Myoban in Beppu, carrying sulfur as a second character: strongly acidic enough to sting slightly on contact, colorless and clear, with a tart taste and the faint rotten-egg note of H₂S. It is lightly mineralized overall, yet rich in metasilicic acid at 153 mg/kg, which leaves a thin silica film on the skin and places it in the beauty-water family despite its acidity. Among Japan's hottest natural sources; the analysed sample was taken from the storage basin rather than the wellhead.
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.
- Hydrogenmakes the water acidic — sharp and bactericidalH⁺2.5mgP70 national43%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺20.2mgP38 national17%
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺20.7mgP4 national16%
- Magnesiummild; a laxative if you drink itMg²⁺8.3mgP59 national12%
- Aluminumshows up in acidic volcanic waterAl³⁺4.3mgP83 national8%
- Potassiumminor; matters for drinking limitsK⁺5.1mgP34 national2%
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺2.4mgP76 national2%
- ManganeseMn²⁺0.70mgP73 national0.5%
- StrontiumSr²⁺0.20mgP41 national0.0%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻254mgP70 national94%
- HSO4HSO421.4mgP60 national4%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻3.3mgP4 national2%
- H2PO4H₂PO₄⁻0.50mgP88 national0.2%
- ThiosulfateS₂O₃²⁻0.40mgP60 national0.2%
- FluorideF⁻0.20mgP16 national0.2%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃153mgP69 national
- H2SO4FreeH2SO4Free0.10mgP67 national
- Phosphoric acidH₃PO₄0.0000mg
- Metaarsenious acidHAsO₂0.0000mg
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂0.0000mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂9.7mgP40 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S9.0mgP91 national
- ArsenicAs< —mg
- CadmiumCd< —mg
- CopperCu< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —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