A calcium- and sodium-led chloride spring sitting right at isotonic mineralization (9.1 g/kg dissolved solids) — close to seawater concentration, with strong heat-retaining body. At the wellhead the water carries a salty-bitter tang and a faint hint of hydrogen sulfide, giving it a distinctly mineral character.
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, netto 熱の湯).
cold sensitivity
Skin conditions
Sulfur and acidic waters are antibacterial and keratolytic, studied for atopic dermatitis and psoriasis.
atopic skin, eczema
Circulation
Skin-absorbed CO₂ and hydrogen sulfide relax the vessel walls; carbon-dioxide springs can raise peripheral blood flow several-fold.
tired legs
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
Sensitive-skin caution
Strongly acidic or sulfur-rich water can sting broken, atopic-flare, or dry elderly skin. Ease in slowly and rinse off if it stings.
broken or dry skin
From a certificate analyzed in 2023.
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 (especially when fever is present)
- Active tuberculosis
- Malignant tumor
- Severe heart disease
- Respiratory failure
- Renal failure
- Bleeding disorders
- Severe anemia
- Any illness in an actively progressing stage
- Pregnancy (especially the early and late stages) (dropped from the official list in 2014)
- Kidney disease
- Hypertension, any other condition with edema
- Hyperthyroidism (iodine-containing springs are contraindicated)
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⁺2,042mgP98 national63%
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺1,327mgP89 national36%
- MagnesiumMg²⁺8.5mgP60 national0.4%
- PotassiumK⁺22.3mgP67 national0.3%
- FeTotalFe0.30mgP56 national
- Manganesetrace; companion to iron springsMn²⁺0.30mgP54 national
- Aluminumshows up in acidic volcanic waterAl³⁺< —mg
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻5,694mgP94 national100%
- BicarbonateHCO₃⁻13.7mgP9 national0.1%
- Thiosulfateoxidized sulfurS₂O₃²⁻0.40mgP60 national
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻0.40mgP4 national
- BO2BO₂⁻< —mg
- Carbonatestrongly alkaline; slippery feelCO₃²⁻< —mg
- Fluoridetrace; drinking limits applyF⁻< —mg
- Hydrogen sulfidesulfur character — antibacterialHS⁻< —mg
- HSiO3HSiO₃⁻< —mg
- HydroxideOH⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃23.3mgP8 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂< —mg
- Free carbon dioxideCO₂0.40mgP14 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S2.1mgP80 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 2023.
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.
- Neuralgia
- Muscle pain
- Joint pain
- Frozen shoulder
- Motor paralysis
- Joint stiffness
- Bruises
- Sprains
- Chronic digestive disorders
- Chronic digestive disorders
- Chronic constipation
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.
- Tei C, Kihara T. Waon Therapy for Chronic Heart Failure. J. Cardiology 53(2):214–218, 2009.
- Coavoy-Sánchez SA et al. Hydrogen sulfide and dermatological diseases. Int. J. Dermatology, 2019.
- Naito Y et al. A Hot-Spring Water Improves Inflammatory Conditions in an Atopic Dermatitis Model. Biomedicines 13(11):2707, 2025.
- Akiyama H et al. Antimicrobial effects of acidic hot-spring water on S. aureus. J. Dermatological Science 24(3):193–200, 2000.
- Toriyama T et al. Carbon dioxide foot bathing on critical limb ischemia. International Angiology 21(4):367–373, 2002.
- Takeda M et al. Hot spring bathing practices have a positive effect on mental health in Japan. Heliyon 9(9):e19631, 2023.
- Ministry of the Environment, Japan. 禁忌症及び入浴又は飲用上の注意事項 (2014 notice).official