Waka-no-Yu Spring
Analysis UnverifiedKusatsu Onsen, renowned as a 'yakuto' (medicinal spring) since ancient times, drew people seeking therapeutic benefits during the Edo period. Here, Wakanoyu stands as a naturally gushing source, preserving Kusatsu's rich hot spring culture to this day. Its distinctly acidic waters offer a tingling sensation that invigorates both mind and body, leaving you feeling remarkably light and refreshed after your bath. This spring is highly recommended for those suffering from chronic skin issues or sensitivity to cold, and for anyone seeking deep relaxation and rejuvenation from daily stress.
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.
A natural moisturizer also used in skincare lotions. Forms a thin veil on the skin to reduce moisture loss after bathing.
Mild antibacterial action keeps the skin clean. Trace transdermal absorption supports tooth and bone health.
- Sulfur5.6 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.
- Acidic (pH)pH 2
- 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)327 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.
- Sulfate701 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 acid234 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 temperature50.5℃
- 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 potent acidity—pH 2.0—newcomers should begin with brief 3-5 minute soaks, carefully observing skin response before gradually extending time. After bathing, tradition calls for patting dry without rinsing away the mineral essence; however, those with sensitive skin should opt for a gentle lukewarm rinse. Bathe once or twice daily, hydrating generously with a full cup of water both before and after immersion.
The 50.5°C waters of this powerfully acidic spring—pH 2.0—deliver sulfate ions (701 mg), chloride ions (327 mg), and metasilicic acid (234 mg) that gently refine skin texture and show remarkable efficacy against stubborn conditions: atopic dermatitis, psoriasis, and chronic eczema. The hydrogen sulfide compounds further enhance peripheral circulation, addressing cold sensitivity, fatigue, and melancholic states through profound systemic renewal.
Those with sensitive skin, delicate mucous membranes, or age-related xerosis should refrain from bathing. Due to the strong acidity, rinse thoroughly in warm water post-bath, monitor closely for thermal illness (onset 3 days–1 week), and start conservatively with short, infrequent soaks.
※ See the analysis data below for detailed contraindications
ANALYSIS DATAView all analysis fields ▼
Source Info
- Source name
- Waka-no-Yu Spring
- Spring type
- Acidic sulfur-containing aluminum sulfate chloride spring (hydrogen sulfide type) (low-temperature acidic hot spring)
- Source temperature
- 50.5℃
- pH
- 2
- Flow type
- Natural spring
- Osmotic pressure
- Hypotonic
Analysis Document
- Analysis date
- 2019-12-02
- 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⁺
- 10.2 mg/kg
- Sodium ion Na⁺
- 56.1 mg/kg
- Potassium ion K⁺
- 26.9 mg/kg
- Magnesium ion Mg²⁺
- 35.4 mg/kg
- Calcium ion Ca²⁺
- 73.9 mg/kg
- Aluminum ion Al³⁺
- 49.4 mg/kg
- Manganese ion Mn²⁺
- 1.8 mg/kg
- Iron(II) ion Fe²⁺
- 18.8 mg/kg
- Total cations
- 273 mg/kg
Anions
- Fluoride ion F⁻
- 9.3 mg/kg
- Chloride ion Cl⁻
- 327 mg/kg
- Sulfate ion SO₄²⁻
- 701 mg/kg
- Hydrogen sulfate HSO₄⁻
- 242 mg/kg
- Total anions
- 1279 mg/kg
Undissociated Components
- Metasilicic acid H₂SiO₃
- 234 mg/kg
- Metaboric acid HBO₂
- 7.9 mg/kg
- Total undissociated
- 248 mg/kg
Dissolved Gas
- Free carbon dioxide CO₂
- 110 mg/kg
- Free hydrogen sulfide H₂S
- 6.0 mg/kg
- Total dissolved gas
- 116 mg/kg
Totals
- Total dissolved substances
- 1800 mg/kg
- Component total
- 1920 mg/kg
- Evaporation residue
- 1760 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
