Dorogawa Onsen's "Shinsen" source is a gentle simple thermal water, lightly mineralized at 439 mg/kg dissolved solids. Weakly alkaline and soft on the skin, it sits in the Japanese beauty-water family. A generous 101 mg/kg of metasilicic acid leaves the kind of silica film that makes skin feel noticeably smoother afterwards. The source emerges cool at 30.7 °C and qualifies as an onsen by temperature.
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
Recovery
Warmth and buoyancy lower stress markers and improve sleep; habitual bathing is linked to lower rates of depression.
fatigue, stress
Take care
- acute illness (especially with fever)
- active tuberculosis
- malignant tumors
- severe heart disease
- respiratory failure
- renal failure
- hemorrhagic diseases
- severe anemia
- other diseases generally in a progressive state
- pregnancy (especially early and late stages)
- wholly contraindicated regardless of any illness
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⁺87.2mgP26 national
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺8.0mgP23 national
- Magnesiummild; a laxative if you drink itMg²⁺1.3mgP28 national
- AmmoniumNH₄⁺0.70mgP56 national
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺0.20mgP39 national
- Potassiumminor; matters for drinking limitsK⁺0.20mgP2 national
- Aluminumshows up in acidic volcanic waterAl³⁺0.10mgP54 national
- Manganesetrace; companion to iron springsMn²⁺< —mg
- ZincZn²⁺< —mg
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻187mgP56 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻24.2mgP19 national
- Carbonatestrongly alkaline; slippery feelCO₃²⁻9.6mgP50 national
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻3.2mgP12 national
- Fluoridetrace; drinking limits applyF⁻3.0mgP66 national
- Hydrogen sulfidesulfur character — antibacterialHS⁻0.90mgP69 national
- Hydrogen phosphateHPO₄²⁻0.20mgP54 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃101mgP55 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂9.5mgP53 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂< —mg
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S< —mg
- ArsenicAs0.01mgP24 national
- CadmiumCd< —mg
- CopperCu< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —mg
Measured at the source
On the certificate
- neuralgia
- muscle pain
- joint pain
- frozen shoulder
- motor paralysis
- stiffness of joints
- bruises
- sprains
- chronic digestive disorders
- hemorrhoids
- sensitivity to cold
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.
- 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.