大涌谷温泉 蒸気造成混合泉３号線（強羅方面）Owakudani Onsen Steam-Generated Blended Spring Line No. 3 (Gora direction)
An acidic calcium sulfate-chloride spring generated from the volcanic steam of Owakudani. At pH 2.2 it is strongly acidic, sharp enough to prickle slightly on the skin, and the kind of water with a track record on stubborn skin conditions. The source emerges hot in the high-50s Celsius and carries 123 mg/kg of metasilicic acid.
Good for
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
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
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, nettō 熱の湯).
cold sensitivity
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
- people with sensitive skin or mucous membranes
- skin dryness in the elderly
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.
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺114mgP75 national
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺39.0mgP8 national
- Magnesiummild; a laxative if you drink itMg²⁺37.3mgP81 national
- Aluminumshows up in acidic volcanic waterAl³⁺14.5mgP91 national
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺9.5mgP87 national
- Hydrogenmakes the water acidic — sharp and bactericidalH⁺6.4mgP80 national
- Potassiumminor; matters for drinking limitsK⁺3.4mgP28 national
- Manganesetrace; companion to iron springsMn²⁺1.8mgP89 national
- StrontiumSr²⁺0.08mgP16 national
- ZincZn²⁺0.04mgP66 national
- LithiumLi⁺0.0000mg
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻540mgP88 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻216mgP56 national
- HSO4HSO4114mgP70 national
- NitrateNO₃⁻0.61mgP64 national
- Fluoridetrace; drinking limits applyF⁻0.13mgP10 national
- Bromidetrace, sea-originBr⁻0.0000mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃123mgP63 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂4.0mgP30 national
- H2SO4FreeH2SO4Free2.0mgP75 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.03mgP53 national
- ArsenicAs0.0060mgP17 national
- CadmiumCd0.0000mg
- CopperCu0.0000mg
- Mercurytoxic trace — part of the drinking-safety checkHg0.0000mg
- LeadPb0.0000mg
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