An acidic, sulfur-bearing simple thermal spring in the Myoban district of Beppu. Strongly acidic, it is sharp enough to sting slightly on contact, and the water runs pale white and faintly cloudy with a hydrogen sulfide note and a slightly astringent taste. Metasilicic acid is unusually high for this type, at 166 mg/kg. The facility's own poster explains that, because of the water's character, the private baths have no showers or air conditioning, and it lists atopic skin and eczema among the effects.
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⁺4.0mgP75 national53%
- Aluminumshows up in acidic volcanic waterAl³⁺12.9mgP91 national19%
- Sodiumsalt's cation: pairs with chloride to make the water saltyNa⁺17.3mgP3 national10%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺13.8mgP30 national9%
- Magnesiummild; a laxative if you drink itMg²⁺3.7mgP43 national4%
- Potassiumminor; matters for drinking limitsK⁺6.5mgP38 national2%
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺3.5mgP79 national2%
- AmmoniumNH₄⁺0.20mgP29 national0.1%
- ManganeseMn²⁺0.10mgP37 national0.0%
- StrontiumSr²⁺0.10mgP24 national0.0%
- ZincZn²⁺< —mg
- Sulfate"gypsum / Glauber's salt": vessels and wound healingSO₄²⁻337mgP77 national92%
- HSO4HSO445.2mgP64 national6%
- Chloridetable-salt anion: coats the skin and holds heat inCl⁻4.1mgP5 national2%
- ThiosulfateS₂O₃²⁻1.3mgP75 national0.3%
- H2PO4H₂PO₄⁻0.60mgP95 national0.1%
- BromideBr⁻0.40mgP41 national0.1%
- NitrateNO₃⁻0.10mgP26 national0.0%
- Metasilicic acidmetasilicic acid: a natural moisturizer for silky skinH₂SiO₃166mgP76 national
- Metaboric acidmetaboric acid: mildly antibacterialHBO₂0.90mgP12 national
- H2SO4FreeH2SO4Free0.50mgP70 national
- Free carbon dioxidefizz: widens blood vessels (strong above 1000 mg/kg)CO₂8.8mgP38 national
- Free hydrogen sulfide"egg" smell: opens vessels, antibacterialH₂S2.8mgP82 national
- Mercurytoxic trace: part of the drinking-safety checkHg0.0006mgP52 national
- ArsenicAs< —mg
- 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