幕岩源泉Makuiwa Spring
A simple sulfur spring at Shiga Kogen's Makuiwa Onsen. The source emerges at 71 °C — among Japan's hottest natural sources — with near-neutral pH 6.47 and hypotonic mineralization. Free H₂S of 8.3 mg/kg classifies it as a sulfur spring and carries the characteristic rotten-egg note. Mineralization is light overall, but the sulfur signature and the heat give the water real presence.
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
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⁺23.3mgP5 national
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺20.7mgP39 national
- Magnesiummild; a laxative if you drink itMg²⁺6.5mgP57 national
- Potassiumminor; matters for drinking limitsK⁺3.4mgP28 national
- AmmoniumNH₄⁺0.80mgP59 national
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺0.10mgP29 national
- Manganesetrace; companion to iron springsMn²⁺0.10mgP36 national
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻59.2mgP33 national
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻46.8mgP40 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻16.3mgP15 national
- Hydrogen sulfidesulfur character — antibacterialHS⁻2.9mgP82 national
- Fluoridetrace; drinking limits applyF⁻0.10mgP8 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃73.2mgP45 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂10.4mgP57 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂53.1mgP69 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S8.3mgP91 national
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.
- 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