ラムネ温泉Ramune Spring
A rare carbonated spring that earns its name — fine bubbles cling to the skin the moment you enter. The wellhead is a cool 31.5 °C and free CO2 reaches 1,400 mg/kg, so bathers stay in long while the carbonation tingles. The base chemistry is a magnesium-sodium bicarbonate water, neutral pH and lightly mineralized, with a generous 172 mg/kg of metasilicic acid adding softness to the skin feel.
Good for
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
Circulation
Skin-absorbed CO₂ and hydrogen sulfide relax the vessel walls; carbon-dioxide springs can raise peripheral blood flow several-fold.
tired legs
Recovery
Warmth and buoyancy lower stress markers and improve sleep; habitual bathing is linked to lower rates of depression.
fatigue, stress
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.
- Magnesiummild; a laxative if you drink itMg²⁺143mgP93 national43%
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺215mgP52 national34%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺101mgP72 national18%
- Potassiumminor; matters for drinking limitsK⁺36.5mgP79 national3%
- Iron (II)Fe²⁺2.9mgP79 national0.4%
- LithiumLi⁺0.60mgP61 national0.3%
- AmmoniumNH₄⁺0.90mgP61 national0.2%
- ManganeseMn²⁺0.90mgP79 national0.1%
- StrontiumSr²⁺0.60mgP69 national0.0%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻1,250mgP92 national76%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻193mgP67 national15%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻83.8mgP37 national9%
- FluorideF⁻0.40mgP33 national0.1%
- H2PO4H₂PO₄⁻0.20mgP50 national0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃172mgP79 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂4.2mgP32 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂1,400mgP100 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.0000mg
- ArsenicAs0.0050mgP20 national
- CadmiumCd< —mg
- CopperCu< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —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.
- Toriyama T et al. Carbon dioxide foot bathing on critical limb ischemia. International Angiology 21(4):367–373, 2002.
- 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.