黒川温泉 山河旅館 低温源泉Kurokawa Onsen Sanga Ryokan Lower-Temp Spring
The lower-temperature wellhead at Sanga Ryokan in Kurokawa Onsen (49.3 °C). Lightly mineralized at 757 mg/kg, this simple sulfur spring of the hydrogen sulfide type carries 4.3 mg/kg of free H₂S — enough to lend the bath a soft rotten-egg note. Neutral pH keeps the feel gentle; metasilicic acid at 67 mg/kg adds a touch of skin-smoothing softness.
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
- General contraindications: acute illness (especially when fever is present), active tuberculosis, malignant tumor, severe heart disease, respiratory failure, renal failure, bleeding disorders, severe anemia, pregnancy (especially the early and late stages), any illness in an actively progressing stage
- Contraindications specific to this spring: dry skin in the elderly
- Contraindications for drinking: kidney disease, hypertension, any other condition with edema
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⁺144mgP39 national62%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺37.3mgP50 national18%
- Potassiumminor; matters for drinking limitsK⁺34.0mgP78 national9%
- Magnesiummild; a laxative if you drink itMg²⁺10.5mgP63 national8%
- LithiumLi⁺1.4mgP85 national2%
- Iron (II)Fe²⁺1.1mgP64 national0.4%
- AluminumAl³⁺0.30mgP67 national0.3%
- ManganeseMn²⁺0.60mgP69 national0.2%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻233mgP68 national48%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻145mgP49 national40%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻73.2mgP38 national12%
- FluorideF⁻0.40mgP28 national0.2%
- Hydrogen sulfideHS⁻0.50mgP55 national0.1%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃67.3mgP42 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂8.8mgP51 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂123mgP82 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S4.3mgP84 national
- ArsenicAs0.06mgP56 national
- CopperCu0.02mgP85 national
Measured at the source
On the certificate
- General indications: neuralgia, muscle pain, joint pain, frozen shoulder, motor paralysis, joint stiffness, bruises, sprains, chronic digestive disorders, hemorrhoids, cold sensitivity, convalescence, fatigue recovery, general health improvement
- Indications of this spring: hypertension, arteriosclerosis, chronic skin conditions, chronic gynecological conditions, cuts, diabetes
- Chronic digestive disorders, chronic constipation
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