A 52 °C hot simple thermal spring in Beppu's Nakajima district, neutral pH and hypotonic. Total dissolved solids are light at 872 mg/kg, but metasilicic acid runs a generous 200 mg/kg — enough to leave a thin silica film that makes skin feel noticeably smoother. Colorless, clear, tasteless and odorless at the source, very gentle on the body.
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
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
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⁺25.1mgP43 national15%
- ManganeseMn²⁺0.40mgP59 national0.2%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻79.8mgP35 national24%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃200mgP85 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂7.7mgP48 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂3.5mgP25 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.
- Naito Y et al. A Hot-Spring Water Improves Inflammatory Conditions in an Atopic Dermatitis Model. Biomedicines 13(11):2707, 2025.
- 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.