Hosen-no-yu
Analysis VerifiedHousen-no-Yu, a precious spring at Kusatsu Onsen, one of Japan's three most famous hot springs, has naturally gushed from bedrock for approximately 1200 years. Distinct from major sources like Yubatake and Bandaiko, this rare water gently envelops the skin with its sulfurous aroma. Its crisp quality offers a sensation of purifying both mind and body. After bathing, your skin will feel wonderfully silky, and the restorative warmth from deep within will invite deep relaxation, supporting overall rejuvenation. It is highly recommended for those seeking to escape daily life and reset themselves with a truly special hot spring experience.
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.
- Sulfur6.2 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)274 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.
- Sulfate596 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 acid208 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 temperature45℃
- 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.
With a highly acidic pH of 2.0, those with sensitive skin and the elderly should be cautious of "yu-atari" (onsen sickness). Start with short dips to acclimate your body. The water will sting eyes and open wounds, so be careful when splashing or pouring water.
Known for its powerful sterilizing effects, this spring has a potent acidity of pH 2.0. Furthermore, it contains 208 mg/kg of metasilicic acid, said to promote skin metabolism and beautifying effects. It has been used for therapeutic bathing by those with skin concerns like atopic dermatitis and chronic eczema.
Avoid bathing during active phases of illness or if you are extremely weak. Due to the strong acidity, individuals with sensitive skin, mucous membranes, or xeroderma (dry skin) in the elderly should be particularly cautious.
※ See the analysis data below for detailed contraindications
ANALYSIS DATAView all analysis fields ▼
Source Info
- Source name
- Hosen-no-yu
- Spring type
- 酸性・含硫黄-アルミニウム-硫酸塩・塩化物温泉（硫化水素型）
- Source temperature
- 45℃
- pH
- 2
- Flow rate
- 72.2 L/min
- Flow type
- 自然湧出
- Osmotic pressure
- 低張性
Analysis Document
- Analysis date
- 2015-05-21
- 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)
Cations
- Hydrogen ion H⁺
- 9.8 mg/kg
- Sodium ion Na⁺
- 46.4 mg/kg
- Potassium ion K⁺
- 24.4 mg/kg
- Magnesium ion Mg²⁺
- 33.1 mg/kg
- Calcium ion Ca²⁺
- 69.9 mg/kg
- Aluminum ion Al³⁺
- 43.3 mg/kg
- Manganese ion Mn²⁺
- 1.7 mg/kg
- Iron(II) ion Fe²⁺
- 15.2 mg/kg
- Total cations
- 244 mg/kg
Anions
- Fluoride ion F⁻
- 8.4 mg/kg
- Chloride ion Cl⁻
- 274 mg/kg
- Sulfate ion SO₄²⁻
- 596 mg/kg
- Hydrogen sulfate HSO₄⁻
- 196 mg/kg
- Total anions
- 1074 mg/kg
Undissociated Components
- Sulfuric acid H₂SO₄
- 4.8 mg/kg
- Metasilicic acid H₂SiO₃
- 208 mg/kg
- Metaboric acid HBO₂
- 7.3 mg/kg
- Total undissociated
- 220 mg/kg
Dissolved Gas
- Free carbon dioxide CO₂
- 96.8 mg/kg
- Free hydrogen sulfide H₂S
- 6.6 mg/kg
- Total dissolved gas
- 103 mg/kg
Totals
- Total dissolved substances
- 1540 mg/kg
- Component total
- 1640 mg/kg
- Evaporation residue
- 1360 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
