Unzen Onsen Kojigoku Source
Analysis UnverifiedUnzen Onsen Kojigoku Source rises in Kojigoku, among Unzen's steaming "hells," where a bathhouse for toji cures is said to have opened in 1731, and the scholar Yoshida Shoin is said to have visited. Clear as it gushes, the water turns milky white in the air and soothes the skin with a sulfurous aroma. Plentiful in volume, it suits travelers seeking a rustic, unhurried soak in the Unzen highlands.
The bar length shows how abundant each component is compared to thresholds that make it "distinctive" (therapeutic spring standards, beauty spring criteria, etc.).
The aroma typical of sulfur springs, with circulatory and antibacterial effects.
Absorbed through the skin to gently promote peripheral circulation.
Scores are calculated from mineral analysis data based on the Mineral Spring Analysis Guidelines (Ministry of Environment, Japan). They are unrelated to facility atmosphere or service quality.
▸Note
The temperature, pH and component values shown here are based on the hot spring analysis (source). Actual values in the bath may differ depending on heating, dilution, recycling and filtration. Please check current usage status at the facility.
The source emerges at 51.1°C, so check the temperature near the spout first. As a weakly acidic pH 4.41 water with hydrogen sulfide, avoid long soaks, remove silver jewelry, and rinse lightly afterward if your skin is sensitive.
Holding 2.4 mg/kg of free hydrogen sulfide, this sulfur water has long served toji cures and is valued for immune system stimulation. Its weakly acidic pH 4.41 milky water gently tones the skin, a fitting choice for balneotherapy on tired days.
As the water contains hydrogen sulfide, mind ventilation and leave at once if you feel unwell. The weakly acidic water may irritate sensitive skin, so stop bathing if any discomfort appears.
※ See the analysis data below for detailed contraindications
ANALYSIS DATAView all analysis fields ▼
Source Info
- Source name
- Unzen Onsen Kojigoku Source
- Spring type
- Simple Sulfur Hot Spring (hydrogen sulfide type)
- Old spring type name
- 単純硫化水素温泉
- Source temperature
- 51.1℃
- pH
- 4.41
- Flow type
- 自然湧出
- Osmotic pressure
- 低張性
Analysis Document
- Analysis date
- 2026-02-20
- Analyst organization
- 一般財団法人 佐賀県環境科学検査協会
- Registration No.
- 佐賀県登録41第0002号
Cations
- Lithium ion Li⁺
- 0.00 mg/kg
- Sodium ion Na⁺
- 5.8 mg/kg
- Potassium ion K⁺
- 2.7 mg/kg
- Ammonium ion NH₄⁺
- 2.5 mg/kg
- Magnesium ion Mg²⁺
- 1.6 mg/kg
- Calcium ion Ca²⁺
- 5.7 mg/kg
- Aluminum ion Al³⁺
- 0.90 mg/kg
- Manganese ion Mn²⁺
- 0.00 mg/kg
- Zinc ion Zn²⁺
- 0.00 mg/kg
- Lead ion Pb²⁺
- not detected
- Strontium ion Sr²⁺
- 0.00 mg/kg
- Barium ion Ba²⁺
- 0.00 mg/kg
- Copper ion Cu²⁺
- 0.00 mg/kg
- Cadmium ion Cd²⁺
- not detected
- Total cations
- 0.02 mg/kg
Anions
- Fluoride ion F⁻
- 0.00 mg/kg
- Chloride ion Cl⁻
- 3.5 mg/kg
- Hydroxide ion OH⁻
- 0.00 mg/kg
- Hydrogen sulfide ion HS⁻
- 0.00 mg/kg
- Thiosulfate ion S₂O₃²⁻
- 0.00 mg/kg
- Sulfate ion SO₄²⁻
- 30.5 mg/kg
- Bicarbonate ion HCO₃⁻
- 14.7 mg/kg
- Carbonate ion CO₃²⁻
- 0.00 mg/kg
- Bromide ion Br⁻
- 0.00 mg/kg
- Iodide ion I⁻
- 0.00 mg/kg
- Nitrite ion NO₂⁻
- 0.00 mg/kg
- Nitrate ion NO₃⁻
- 0.00 mg/kg
- Dihydrogen phosphate H₂PO₄⁻
- 0.00 mg/kg
- Total anions
- 0.05 mg/kg
Undissociated Components
- Arsenious acid HAsO₂
- 0.00 mg/kg
- Metasilicic acid H₂SiO₃
- 36.5 mg/kg
- Metaboric acid HBO₂
- 0.00 mg/kg
- Total undissociated
- 0.04 mg/kg
Dissolved Gas
- Free carbon dioxide CO₂
- 121 mg/kg
- Free hydrogen sulfide H₂S
- 2.4 mg/kg
- Total dissolved gas
- 0.12 mg/kg
Totals
- Total dissolved substances
- 0.10 mg/kg
- Component total
- 0.23 mg/kg
- Evaporation residue
- 0.13 mg/kg
Usage
- Heating
- No
- Dilution
- Yes
- Recycle / Filter
- No
- Additives
- No
- Disinfection
- No
Indications & Contraindications
- Bathing indications
- Atopic dermatitis, Plaque psoriasis, Chronic eczema, Epidermal suppuration, Autonomic instability, Insomnia, Depression
- General indications
- High blood pressure (mild), Rheumatoid arthritis, Chronic pain or stiffness in muscles and joints, Muscle stiffness due to motor paralysis, Gastrointestinal dysfunction
- Contraindications
- Acute illness (especially with fever), Active tuberculosis, Malignant tumors, Severe heart disease, Respiratory failure, Renal failure, Bleeding disorders, Severe anemia, Any actively progressing illness, Pregnancy (especially early and late stages), Severe chronic dermatitis (sulphur springs)
Drinking
- Drinkability
- Not drinkable
