A hot sodium chloride spring rising at a remarkable 93.2 °C wellhead temperature — one of the hottest sources in Beppu's catalogue. Weakly acidic at pH 6.67 and moderately mineralized at 3.76 g/kg, with chloride dominating the anion profile and leaving a salty, heat-retaining film on the skin after bathing.
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
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
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
- 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.
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺1,127mgP87 national89%
- Potassiumminor; matters for drinking limitsK⁺175mgP96 national8%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺28.1mgP44 national3%
- MagnesiumMg²⁺3.6mgP43 national0.5%
- ManganeseMn²⁺0.90mgP76 national0.1%
- Iron (II)Fe²⁺0.30mgP43 national0.0%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻1,776mgP86 national87%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻64.3mgP46 national2%
- BicarbonateHCO₃⁻30.6mgP19 national0.9%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃217mgP89 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂64.3mgP92 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂18.5mgP49 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
- Hemorrhoids
- Cold sensitivity
- Chronic skin conditions (dropped from the official list in 2014)
- Chronic gynecological 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.
- Takeda M et al. Hot spring bathing practices have a positive effect on mental health in Japan. Heliyon 9(9):e19631, 2023.