Oku no Yu
Analysis VerifiedOku-no-yu, naturally gushing from the profound wilderness of Noboribetsu Onsen—Hokkaido's premier hot spring town renowned for its dramatic “Jigokudani” (Hell Valley)—offers a unique experience. Its milky white, soft waters gently envelop the skin, while the subtle sulfur aroma helps one forget the daily grind. The warmth slowly permeates to the body's core, providing a pleasant, long-lasting restorative warmth. This blessing from nature, cherished by therapeutic bathers for ages, deeply soothes both mind and body, appealing to those who wish to fully immerse themselves in the essence of onsen.
The bar length shows how abundant each component is compared to thresholds that make it "distinctive" (therapeutic spring standards, beauty spring criteria, etc.).
Undissociated boric acid with antibacterial action that keeps the skin surface clean.
The source of the distinctive sulfur smell. Dilates blood vessels via skin and inhalation to strongly boost circulation.
A natural moisturizer also used in skincare lotions. Forms a thin veil on the skin to reduce moisture loss after bathing.
- Sulfur25.6 mg/kg
- Feel
- Smells like boiled eggs; the water may turn milky white or blue-green.
- Said to
- Said to be strongly antibacterial and to promote circulation. Bathing indications include atopic dermatitis and chronic eczema.
- Note
- With sensitive skin, rinse with fresh water after bathing. Remove silver jewelry—it tarnishes.
- Chloride (salt)809 mg/kg
- Feel
- Tastes salty; the warmth lasts after you get out.
- Said to
- Salt is said to form a film on the skin that keeps in heat and moisture. Bathing indications include cuts, poor circulation and dry skin.
- Note
- May sting cuts. Strong salty water can tire you—avoid long soaks.
- Metasilicic acid148 mg/kg
- Feel
- Your skin may feel smoother.
- Said to
- 50 mg/kg or more is said to mark a “skin-beautifying spring”; it is also used in skincare.
- Note
- The “skin-beautifying” label is a common rule of thumb, not a legal standard.
- Source temperature73.3℃
- Feel
- The source is 42°C or hotter; the bath may be on the hot side.
- Said to
- Heat is said to boost circulation and warm the body.
- Note
- Older people and those with high blood pressure or heart conditions should avoid baths of 42°C or more. Keep soaks short.
Effects are general descriptions based on the Ministry of the Environment’s indications by spring type, not a guarantee.
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.
Given its sulfur-rich composition and high temperature (73.3°C from source), verify that water has been appropriately cooled or diluted before entry. Due to its weakly acidic nature (pH 4.76), initial sessions should be limited to 10–15 minutes to acclimate your skin. After bathing, rinse briefly with shower water to prevent excessive sulfur residue; complete the rinse swiftly to preserve therapeutic minerals on your skin.
The weakly acidic pH 4.76 and hydrogen sulfide-type sulfur compounds gently exfoliate skin, offering relief for those with atopic dermatitis and chronic dermatological conditions. Sodium and calcium chloride minerals penetrate deeply to warm the body core, historically supporting recovery from chronic rheumatoid arthritis and motor nerve dysfunction. With a low osmotic concentration of 1.699g/kg total dissolved solids, this spring's mild mineral intensity suits prolonged therapeutic bathing courses.
Those with serious cardiovascular conditions—heart disease, hypertension, arteriosclerosis—or malignant tumors and active tuberculosis should refrain from bathing. High temperatures demand particular caution: avoid prolonged immersion or bathing after alcohol consumption.
※ See the analysis data below for detailed contraindications
ANALYSIS DATAView all analysis fields ▼
Source Info
- Source name
- Oku no Yu
- Spring type
- Sulfur-containing sodium and calcium chloride spring (hydrogen sulfide type)
- Old spring type name
- 含硫黄ーナトリウム・カルシウム-塩化物泉 (硫化水素型) (弱酸性低張性高温泉)
- Source temperature
- 73.3℃
- pH
- 4.7
- Flow rate
- 75 L/min
- Flow type
- Natural spring
- Osmotic pressure
- Hypotonic
Analysis Document
- Analysis date
- 2008-07-28
- Analyst organization
- 北海道立衛生研究所
- Registration No.
- 北海道第1号
Cations
- Sodium ion Na⁺
- 343 mg/kg
- Potassium ion K⁺
- 80.4 mg/kg
- Ammonium ion NH₄⁺
- 1.3 mg/kg
- Magnesium ion Mg²⁺
- 7.0 mg/kg
- Calcium ion Ca²⁺
- 108 mg/kg
- Aluminum ion Al³⁺
- 0.40 mg/kg
- Manganese ion Mn²⁺
- 0.60 mg/kg
- Iron(II) ion Fe²⁺
- 1.1 mg/kg
- Iron(III) ion Fe³⁺
- 0.60 mg/kg
- Zinc ion Zn²⁺
- 0.00 mg/kg
- Lead ion Pb²⁺
- 0.00 mg/kg
- Copper ion Cu²⁺
- 0.00 mg/kg
- Cadmium ion Cd²⁺
- 0.00 mg/kg
- Total cations
- 543 mg/kg
Anions
- Fluoride ion F⁻
- 0.50 mg/kg
- Chloride ion Cl⁻
- 809 mg/kg
- Hydrogen sulfide ion HS⁻
- 0.10 mg/kg
- Thiosulfate ion S₂O₃²⁻
- 20.5 mg/kg
- Sulfate ion SO₄²⁻
- 32.9 mg/kg
- Bicarbonate ion HCO₃⁻
- 6.1 mg/kg
- Carbonate ion CO₃²⁻
- 0.00 mg/kg
- Total anions
- 869 mg/kg
Undissociated Components
- Arsenious acid HAsO₂
- 0.30 mg/kg
- Metasilicic acid H₂SiO₃
- 148 mg/kg
- Metaboric acid HBO₂
- 81.6 mg/kg
- Total undissociated
- 230 mg/kg
Dissolved Gas
- Free carbon dioxide CO₂
- 43.0 mg/kg
- Free hydrogen sulfide H₂S
- 14.6 mg/kg
- Total dissolved gas
- 57.6 mg/kg
Trace Components
- Radon Rn
- 0.011 mE/kg
Totals
- Component total
- 1699 mg/kg
- Evaporation residue
- 1683 mg/kg
Usage
- Heating
- No
- Dilution
- Yes
- Recycle / Filter
- Recycled
- Additives
- No
- Disinfection
- Yes
Indications & Contraindications
- Bathing indications
- Atopic dermatitis, Plaque psoriasis, Chronic eczema, Epidermal suppuration, Cuts and grazes, Peripheral circulatory failure, Poor circulation, Depression, Xeroderma
- General indications
- High blood pressure (mild), Rheumatoid arthritis, Autonomic instability, Insomnia, 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
