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
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
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
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
From a certificate analyzed in 2009.
Analyzed before the 2014 revision of the official list, so some wording may be out of date.
- 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⁺114mgP77 national
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺39.0mgP8 national
- Magnesiummild; a laxative if you drink itMg²⁺37.3mgP82 national
- Aluminumshows up in acidic volcanic waterAl³⁺14.5mgP92 national
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺9.5mgP88 national
- Hydrogenmakes the water acidic — sharp and bactericidalH⁺6.4mgP80 national
- Potassiumminor; matters for drinking limitsK⁺3.4mgP27 national
- Manganesetrace; companion to iron springsMn²⁺1.8mgP89 national
- StrontiumSr²⁺0.08mgP14 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⁻216mgP58 national
- HSO4HSO4114mgP71 national
- NitrateNO₃⁻0.61mgP69 national
- Fluoridetrace; drinking limits applyF⁻0.13mgP9 national
- Bromidetrace, sea-originBr⁻0.0000mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃123mgP62 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂4.0mgP29 national
- H2SO4FreeH2SO4Free2.0mgP77 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.03mgP50 national
- ArsenicAs0.0060mgP18 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