Matogahama Onsen rises in Kitamatogahama, Beppu, as a bicarbonate spring led by sodium with substantial magnesium and calcium, and a chloride sub-type adds a salty edge — the certificate's legacy name reads as an earth-chloride soda water. It is mildly alkaline and soft on the skin, running very faintly yellow but clear at sampling, with almost no taste or smell and a moderate 1,840 mg/kg of dissolved solids. A generous 233 mg/kg of metasilicic acid puts it squarely in Japan's beauty-water family; the posted panel lists cuts, chronic skin conditions and chronic digestive disorders among its documented bathing indications. That same panel states the water is not suitable for drinking, so this is a bathing-only source.
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
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
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, netto 熱の湯).
cold sensitivity
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
Take care
From a certificate analyzed in 2020.
This list uses the wording the Ministry of the Environment replaced in 2014, so it may not match a current certificate. Items marked † were removed from the official list of contraindications then, or include a condition that was. If you have a health condition, ask a doctor before bathing.
- Acute illness
- Active tuberculosis
- Malignant tumor
- Respiratory failure
- Renal failure
- Bleeding disorders
- Severe anemia
- Any illness in a progressive phase
- Pregnancy (especially the early and late stages) (dropped from the official list in 2014)
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⁺228mgP57 national46%
- Magnesiummild; a laxative if you drink itMg²⁺70.0mgP88 national27%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺90.9mgP71 national21%
- Potassiumminor; matters for drinking limitsK⁺43.4mgP83 national5%
- LithiumLi⁺1.0mgP74 national0.7%
- AmmoniumNH₄⁺0.80mgP60 national0.2%
- Iron (II)Fe²⁺0.50mgP53 national0.1%
- ManganeseMn²⁺0.50mgP66 national0.1%
- StrontiumSr²⁺0.60mgP73 national0.1%
- BariumBa²⁺0.20mgP72 national0.0%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻911mgP89 national70%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻160mgP51 national21%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻91.8mgP53 national9%
- FluorideF⁻0.30mgP22 national0.1%
- BromideBr⁻0.40mgP41 national0.1%
- Hydrogen phosphateHPO₄²⁻0.20mgP52 national0.0%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃233mgP92 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂7.5mgP47 national
- Metaarsenious acidHAsO₂0.20mgP67 national
- H2SO4FreeH2SO4Free0.0000mg
- Phosphoric acidH₃PO₄0.0000mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂26.4mgP57 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.0000mg
- ArsenicAs0.12mgP68 national
- CadmiumCd< —mg
- CopperCu< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —mg
Measured at the source
On the certificate
From a certificate analyzed in 2020.
This list uses the wording the Ministry of the Environment replaced in 2014, so it may not match a current certificate. Items marked † were dropped from the official list then.
- Chronic digestive disorders
- Hemorrhoids
- Chronic skin conditions (dropped from the official list in 2014)
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.