Yubatake Spring
Analysis UnverifiedThe Yubatake source, an iconic symbol of Kusatsu Onsen, has drawn countless literati, samurai, and commoners since the Edo period. Enveloped by its white steam and the purifying hydrogen sulfide scent, visitors are instantly transported to an extraordinary realm. This powerfully acidic water, with a pH of around 2, remarkably tightens the skin, offering a refreshing sensation akin to rejuvenation. It promises profound satisfaction for those seeking silky skin, deep relaxation from daily stress, and authentic hot spring experiences.
The bar length shows how abundant each component is compared to thresholds that make it "distinctive" (therapeutic spring standards, beauty spring criteria, etc.).
Strong astringent action that tightens skin. A key component of acidic springs, suited to oily or acne-prone skin.
The source of the distinctive sulfur smell. Dilates blood vessels via skin and inhalation to strongly boost circulation.
Mild antibacterial action keeps the skin clean. Trace transdermal absorption supports tooth and bone health.
A natural moisturizer also used in skincare lotions. Forms a thin veil on the skin to reduce moisture loss after bathing.
A trace component with gentle antibacterial and anti-inflammatory action.
- Sulfur5.8 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.
- Acidic (pH)pH 2.02
- Feel
- May tingle on the skin; tastes sour.
- Said to
- Said to be strongly antibacterial. Bathing indications include atopic dermatitis and plaque psoriasis.
- Note
- Can irritate sensitive skin—rinse with fresh water after bathing. Keep it out of your eyes.
- Chloride (salt)329 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.
- Sulfate674 mg/kg
- Feel
- Your skin feels moist; the water may taste slightly bitter.
- Said to
- Said to retain heat well and help heal cuts. Bathing indications include cuts and dry skin.
- Note
- It warms you well—do not stay in too long.
- Metasilicic acid243 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 temperature52.3℃
- 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 the strong acidity (pH 2.02), limit your first immersion to 3–5 minutes while monitoring your skin's response before gradually extending duration. The traditional practice is to pat dry with a towel without rinsing away thermal minerals; however, those with sensitive skin may gently rinse with warm water to reduce irritation. Begin with one to two daily immersions, progressively increasing to two or three as your body acclimates—this is the Kusatsu way.
At 52.3°C and pH 2.02, the potent acidity tightens skin surface while free hydrogen sulfide (6.2 mg/kg) delivers antimicrobial and anti-inflammatory benefits, offering scientific grounding for treating atopic dermatitis, psoriasis, and chronic eczema. Those managing glucose intolerance, peripheral circulatory disorders, and cold sensitivity find measurable improvement. Rich in sulfate ions (674.4 mg/kg), this water is widely utilized for alleviating chronic joint and muscle tension.
Those with hypersensitive skin and mucous membranes, and elderly individuals prone to xerosis, should avoid this spring. Those with active disease, severe cardiopulmonary or renal conditions, or active bleeding should refrain from bathing. Due to strong acidity, those with delicate skin should rinse gently in warm water after bathing.
※ See the analysis data below for detailed contraindications
ANALYSIS DATAView all analysis fields ▼
Source Info
- Source name
- Yubatake Spring
- Spring type
- Acidic, sulfur-containing, aluminum, sulfate, chloride hot spring (hydrogen sulfide type) (low-tension acidic high-temperature spring)
- Source temperature
- 52.3℃
- pH
- 2.02
- Flow type
- Natural spring
- Osmotic pressure
- Hypotonic
Analysis Document
- Analysis date
- 2023-08-04
- Analyst organization
- 一般社団法人 群馬県薬剤師会（環境衛生試験センター）
- Registration No.
- 群馬薬第2号
Cations
- Hydrogen ion H⁺
- 10.0 mg/kg
- Sodium ion Na⁺
- 59.7 mg/kg
- Potassium ion K⁺
- 30.0 mg/kg
- Ammonium ion NH₄⁺
- 0.50 mg/kg
- Magnesium ion Mg²⁺
- 39.4 mg/kg
- Calcium ion Ca²⁺
- 73.1 mg/kg
- Aluminum ion Al³⁺
- 49.1 mg/kg
- Manganese ion Mn²⁺
- 2.0 mg/kg
- Iron(II) ion Fe²⁺
- 17.8 mg/kg
- Total cations
- 282 mg/kg
Anions
- Fluoride ion F⁻
- 10.1 mg/kg
- Chloride ion Cl⁻
- 329 mg/kg
- Sulfate ion SO₄²⁻
- 674 mg/kg
- Hydrogen sulfate HSO₄⁻
- 227 mg/kg
- Total anions
- 1241 mg/kg
Undissociated Components
- Metasilicic acid H₂SiO₃
- 243 mg/kg
- Metaboric acid HBO₂
- 9.8 mg/kg
- Total undissociated
- 258 mg/kg
Dissolved Gas
- Free carbon dioxide CO₂
- 46.9 mg/kg
- Free hydrogen sulfide H₂S
- 6.2 mg/kg
- Total dissolved gas
- 53.1 mg/kg
Totals
- Total dissolved substances
- 1780 mg/kg
- Component total
- 1830 mg/kg
- Evaporation residue
- 1620 mg/kg
Usage
- Heating
- No
- Dilution
- No
- Recycle / Filter
- No
- Additives
- No
- Disinfection
- No
Indications & Contraindications
- Bathing indications
- Atopic dermatitis, Plaque psoriasis, Chronic eczema, Epidermal suppuration, Impaired glucose tolerance (diabetes), 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), Sensitive skin or mucous membranes, eye conditions (acidic springs)
Drinking
- Drinkability
- Not drinkable
