地獄温泉(すずめ湯混合泉)Jigoku Onsen (Suzume-no-yu Blended Spring)
A strongly acidic (pH 2.8) sulfur-bearing simple-thermal spring — an opalescent, milky-white water with a moderately astringent bite and a powerful rotten-egg note of H₂S. Free hydrogen sulfide runs to 9.3 mg/kg and total sulfur reaches 8.8 mg/kg, well into the sulfur-bearing band; metasilicic acid at 166 mg/kg adds a faint silica film on top of the pricking, distinctly sulfurous bite that defines the bathhouse's signature Suzume-no-yu pool.
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
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.
- Hydrogenmakes the water acidic — sharp and bactericidalH⁺1.7mgP71 national29%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺24.7mgP42 national21%
- Magnesiummild; a laxative if you drink itMg²⁺9.7mgP61 national14%
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺18.2mgP4 national14%
- AmmoniumNH₄⁺8.8mgP94 national8%
- Aluminumshows up in acidic volcanic waterAl³⁺4.3mgP83 national8%
- Potassiumminor; matters for drinking limitsK⁺8.9mgP43 national4%
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺2.3mgP74 national1%
- ManganeseMn²⁺0.40mgP59 national0.3%
- Iron (III)Fe³⁺0.10mgP58 national0.1%
- StrontiumSr²⁺0.30mgP55 national0.1%
- BariumBa²⁺< —mg
- CopperCu²⁺< —mg
- LithiumLi⁺< —mg
- ZincZn²⁺< —mg
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻270mgP71 national96%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻6.4mgP9 national3%
- FluorideF⁻0.40mgP31 national0.4%
- Hydrogen phosphateHPO₄²⁻0.40mgP69 national0.1%
- Bromidetrace, sea-originBr⁻< —mg
- Carbonatestrongly alkaline; slippery feelCO₃²⁻< —mg
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻< —mg
- Hydrogen sulfidesulfur character — antibacterialHS⁻< —mg
- Iodideyellows in air; helps blood lipidsI⁻< —mg
- NitrateNO₃⁻< —mg
- HydroxideOH⁻< —mg
- Thiosulfateoxidized sulfurS₂O₃²⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃166mgP75 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂4.3mgP32 national
- Metaarsenious acidHAsO₂< —mg
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S9.3mgP92 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂< —mg
- ArsenicAs< —mg
- ChromiumCr< —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.
- 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