An iron-rich simple thermal spring of the sulfate sub-type (formerly classified as tanjun-ryokuban-sen). It carries a good deal of iron and oxidizes reddish-brown on contact with air, while a pH of 3.31 makes it acidic and faintly tangy on the skin. With about 35 mg/kg of dissolved iron and 117.7 mg/kg of metasilicic acid, it sits firmly in the iron-bearing family.
Good for
Skin conditions
Sulfur and acidic waters are antibacterial and keratolytic, studied for atopic dermatitis and psoriasis.
atopic skin, eczema
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.
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺73.5mgP23 national
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺33.1mgP97 national
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺20.5mgP39 national
- Potassiumminor; matters for drinking limitsK⁺17.9mgP59 national
- Magnesiummild; a laxative if you drink itMg²⁺4.3mgP45 national
- Iron (III)Fe³⁺2.2mgP90 national
- ZincZn²⁺0.80mgP94 national
- Manganesetrace; companion to iron springsMn²⁺0.70mgP72 national
- Hydrogenmakes the water acidic — sharp and bactericidalH⁺0.50mgP64 national
- LithiumLi⁺0.50mgP55 national
- AmmoniumNH₄⁺0.40mgP43 national
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻282mgP72 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻65.2mgP31 national
- Fluoridetrace; drinking limits applyF⁻2.3mgP60 national
- Bromidetrace, sea-originBr⁻0.20mgP30 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃118mgP60 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂3.6mgP27 national
- Metaarsenious acidHAsO₂0.80mgP89 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂2.3mgP23 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.20mgP68 national
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.
- 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.
- 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