Kitahama Onsen rises in the Kitahama district of Beppu as a chloride spring led in near-equal measure by sodium, calcium and magnesium, with a bicarbonate sub-type layering in a rounder, softer finish. It is weakly alkaline and easy on the skin, and the certificate records a faintly salty taste at the wellhead. Moderately mineralized at 3,137 mg/kg of dissolved solids, it has real body without feeling heavy. The standout figure is metasilicic acid at 193.8 mg/kg — enough silica to leave the thin moisturizing film that puts this water in Japan's beauty-water family.
Good for
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, nettō 熱の湯).
cold sensitivity
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
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
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⁺516mgP77 national47%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺246mgP87 national26%
- Magnesiummild; a laxative if you drink itMg²⁺135mgP94 national23%
- Potassiumminor; matters for drinking limitsK⁺65.6mgP88 national4%
- LithiumLi⁺1.4mgP86 national0.4%
- Iron (II)Fe²⁺0.70mgP58 national0.1%
- ManganeseMn²⁺0.30mgP53 national0.0%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻1,296mgP82 national76%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻622mgP81 national21%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻54.9mgP41 national2%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃194mgP83 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂4.6mgP35 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂102mgP79 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.
- Kario K et al. Hemodynamic Effects of Hot Spring Bathing. Hypertension Research 46(3):711–720, 2023.
- 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.