A simple sulfur spring from Minamitateishi in Beppu: clear and colorless, but carrying a moderate rotten-egg note of H₂S at the bath inlet. Weakly acidic and faintly tangy, it is lightly mineralized and gentle on the body. Its metasilicic acid content is high enough to leave a thin silica film that makes skin feel smoother, placing it in Japan's beauty-water family. The certificate's sample was drawn at the bath inlet 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.
- Sodiumsalt's cation: pairs with chloride to make the water saltyNa⁺10.8mgP2 national47%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺6.4mgP20 national32%
- Magnesiummild; a laxative if you drink itMg²⁺2.2mgP36 national18%
- Potassiumminor; matters for drinking limitsK⁺1.7mgP19 national4%
- Bicarbonate"soda": softens skin, leaves it smoothHCO₃⁻33.7mgP21 national55%
- Sulfate"gypsum / Glauber's salt": vessels and wound healingSO₄²⁻9.7mgP20 national20%
- Chloridetable-salt anion: coats the skin and holds heat inCl⁻4.7mgP6 national13%
- Thiosulfateoxidized sulfurS₂O₃²⁻5.3mgP93 national9%
- NitrateNO₃⁻1.7mgP90 national3%
- Fluoridetrace; drinking limits applyF⁻< —mg
- Metasilicic acidmetasilicic acid: a natural moisturizer for silky skinH₂SiO₃71.1mgP44 national
- Metaboric acidmetaboric acid: mildly antibacterialHBO₂0.20mgP6 national
- H2SO4FreeH2SO4Free0.0000mg
- Phosphoric acidH₃PO₄0.0000mg
- Metaarsenious acidHAsO₂0.0000mg
- Free carbon dioxidefizz: widens blood vessels (strong above 1000 mg/kg)CO₂73.0mgP75 national
- Free hydrogen sulfide"egg" smell: opens vessels, antibacterialH₂S0.90mgP74 national
- Mercurytoxic trace: part of the drinking-safety checkHg0.0007mgP58 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