Kitahama 2-chome Onsen is a sodium-led chloride spring — salty, heat-retaining water that the poster documents for cold sensitivity, peripheral circulation disorders and dry skin. Bicarbonate accounts for close to a third of the anions, softening what would otherwise be a straightforwardly briny bath, and mineralization is moderate at 2,214 mg/kg. Metasilicic acid runs to 199 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
Take care
- Active stage of any illness (especially with fever)
- Active tuberculosis
- Marked physical debilitation, such as advanced malignant tumor or severe anemia
- Severe heart or lung disease causing breathlessness on slight exertion
- Severe kidney disease accompanied by edema
- Gastrointestinal bleeding
- Visible bleeding
- Acute exacerbation of a chronic 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⁺403mgP71 national58%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺121mgP77 national20%
- Magnesiummild; a laxative if you drink itMg²⁺61.8mgP87 national17%
- Potassiumminor; matters for drinking limitsK⁺44.6mgP82 national4%
- LithiumLi⁺1.5mgP88 national0.7%
- AluminumAl³⁺0.20mgP64 national0.1%
- StrontiumSr²⁺0.30mgP55 national0.0%
- ZincZn²⁺< —mg
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻713mgP78 national64%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻605mgP80 national32%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻53.5mgP41 national4%
- Hydrogen phosphateHPO₄²⁻4.4mgP94 national0.3%
- BromideBr⁻1.8mgP70 national0.1%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃199mgP85 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂5.7mgP40 national
- H2SO4FreeH2SO4Free0.0000mg
- Phosphoric acidH₃PO₄0.0000mg
- Metaarsenious acidHAsO₂0.0000mg
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂30.8mgP62 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S< —mg
- ArsenicAs0.06mgP52 national
- CadmiumCd< —mg
- CopperCu< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —mg
Measured at the source
On the certificate
- Chronic muscle or joint pain and stiffness (rheumatoid arthritis, osteoarthritis, lower back pain, neuralgia, frozen shoulder, bruises, sprains — chronic phase)
- Reduced gastrointestinal function (heaviness, bloating)
- Mild hypertension
- Impaired glucose tolerance (diabetes)
- Mild hypercholesterolemia
- Mild asthma or emphysema
- Hemorrhoid pain
- Stress-related symptoms (sleep disorders, depressed mood)
- Peripheral circulation disorders
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.