Analyzed by the Wakayama Prefectural Environmental Health Research Center, the "Jotoyu No. 2" source is a sodium chloride spring. Hypotonic and moderately mineralized at 1,249 mg/kg of dissolved solids, it is a salty, heat-retaining water; the posting lists nerve pain, muscle pain, joint pain and poor circulation among its indications. For bathing the source is reheated to a comfortable temperature, and recirculation filtration plus a chlorine-based disinfectant are used for hygiene management.
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
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 feverish)
- active tuberculosis
- malignant tumors
- severe heart disease
- respiratory failure
- renal failure
- hemorrhagic diseases
- severe anemia
- other generally progressing illnesses
- pregnancy (especially 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⁺420mgP73 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.
- neuralgia
- muscle pain
- joint pain
- frozen shoulder
- motor paralysis
- joint stiffness
- bruises
- sprains
- chronic digestive disorders
- hemorrhoids
- chronic skin disease (dropped from the official list in 2014)
- chronic gynecological disorders (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.
- Takeda M et al. Hot spring bathing practices have a positive effect on mental health in Japan. Heliyon 9(9):e19631, 2023.