文珠温泉Monju Onsen
A sodium chloride spring tinged with sulfur — the certificate classifies it as sulfur-bearing of the hydrogen sulfide subtype, with a faint rotten-egg note layered over the salty body. Richly mineralized at roughly 12 g/kg and hot enough at 58.8 °C to count as a high-temperature spring, the water carries body and heat retention you can feel as soon as you step in. A generous 121.6 mg/kg of metasilicic acid leaves the kind of thin silica film that makes skin feel noticeably smoother afterwards.
Good for
Warming
Salt forms a film on the skin that slows heat loss, so the warmth lingers long after the bath (the classic heat-keeping water, netto 熱の湯).
cold sensitivity
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⁺3,536mgP95 national82%
- Magnesiummild; a laxative if you drink itMg²⁺225mgP97 national10%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺208mgP86 national6%
- Potassiumminor; matters for drinking limitsK⁺160mgP95 national2%
- LithiumLi⁺4.2mgP94 national0.3%
- AmmoniumNH₄⁺10.1mgP96 national0.3%
- StrontiumSr²⁺13.8mgP95 national0.2%
- ManganeseMn²⁺1.1mgP78 national0.0%
- BariumBa²⁺0.20mgP74 national
- Aluminumshows up in acidic volcanic waterAl³⁺< —mg
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺< —mg
- Iron (III)Fe³⁺< —mg
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻5,448mgP94 national78%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻1,956mgP96 national16%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻503mgP87 national5%
- BromideBr⁻16.9mgP92 national0.1%
- FluorideF⁻1.9mgP59 national0.1%
- Hydrogen sulfideHS⁻0.90mgP66 national0.0%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻0.70mgP16 national
- Iodideyellows in air; helps blood lipidsI⁻< —mg
- SS²⁻< —mg
- Thiosulfateoxidized sulfurS₂O₃²⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃122mgP62 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂43.9mgP86 national
- Metaarsenious acidHAsO₂< —mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂596mgP97 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S2.0mgP80 national
- ArsenicAs< —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.
- Kario K et al. Hemodynamic Effects of Hot Spring Bathing. Hypertension Research 46(3):711–720, 2023.
- 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