A calcium- and sodium-led sulfate spring with sulfate's quiet, mineral-rich body. Alkaline at the wellhead (pH 9.0), the water carries the slippery soft-on-skin feel that puts it in the Japanese 'beauty-water' family. It surfaces at 47 °C — faintly whitish and slightly turbid, with a soft oily note rather than the standard 'clear and odourless' default.
Good for
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
Circulation
Skin-absorbed CO₂ and hydrogen sulfide relax the vessel walls; carbon-dioxide springs can raise peripheral blood flow several-fold.
tired legs
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
From a certificate analyzed in 2005.
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
- Arteriosclerosis (when the water is hot)
- Hypertension (when the water is hot)
- Any illness in an actively progressing stage
- 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.
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺202mgP86 national52%
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺212mgP55 national48%
- PotassiumK⁺2.9mgP26 national0.3%
- MagnesiumMg²⁺0.10mgP11 national0.0%
- CopperCu²⁺0.01mgP72 national
- Manganesetrace; companion to iron springsMn²⁺0.01mgP16 national
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻825mgP94 national87%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻72.4mgP31 national10%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻17.3mgP11 national1%
- Fluoridetrace; drinking limits applyF⁻6.7mgP83 national1%
- Bromidetrace, sea-originBr⁻0.05mgP7 national
- Thiosulfateoxidized sulfurS₂O₃²⁻0.05mgP32 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃47.4mgP26 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂46.3mgP87 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.10mgP58 national
Measured at the source
On the certificate
From a certificate analyzed in 2005.
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
- Cold sensitivity
- Hypertension
- 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.
- 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.
- Toriyama T et al. Carbon dioxide foot bathing on critical limb ischemia. International Angiology 21(4):367–373, 2002.
- 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.