幕岩源泉Makuiwa Spring
An on-site source at Shiga Kogen's Makuiwa Onsen. A genuinely hot spring at 71.2 °C, classified as a simple sulfur water — neutral pH, lightly mineralized at 259 mg/kg total solids. The sulfur side shows clearly: HS⁻ and free H₂S together at roughly 11 mg/kg, enough to give the characteristic rotten-egg note. A generous 73.2 mg/kg of metasilicic acid layers in a smoothing silica film, while the overall composition stays soft rather than aggressive — among Japan's hotter natural sources, but gentle in body.
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⁺23.3mgP5 national
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺20.7mgP38 national
- Magnesiummild; a laxative if you drink itMg²⁺6.5mgP56 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
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻59.2mgP33 national
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻46.8mgP37 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻16.3mgP16 national
- Hydrogen sulfidesulfur character — antibacterialHS⁻2.9mgP80 national
- Fluoridetrace; drinking limits applyF⁻0.10mgP9 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃73.2mgP44 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂10.4mgP57 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂53.1mgP71 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S8.3mgP90 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.
- 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