A sodium-led bicarbonate-sulfate spring carrying a sulfur signature — a hot 50.9 C source from the Naruko field with a layered chemistry. Weakly alkaline at pH 8.5, it gives the soft, slippery feel of Japan's beauty-water family. A generous 259.6 mg/kg of metasilicic acid leaves the kind of silica film that makes skin feel noticeably smoother afterwards.
Good for
Skin conditions
Sulfur and acidic waters are antibacterial and keratolytic, studied for atopic dermatitis and psoriasis.
atopic skin, eczema
Circulation
Skin-absorbed CO₂ and hydrogen sulfide relax the vessel walls; carbon-dioxide springs can raise peripheral blood flow several-fold.
tired legs
Aches & joints
Warmth eases stiffness and raises the pain threshold. Radon and sulfate springs show the strongest evidence for joint and muscle pain.
stiff shoulders
Smooth skin
Bicarbonate and alkalinity gently lift dead keratin while silica hydrates, leaving skin smooth. This is the basis of the beautifying-water (bijin-no-yu 美人の湯) reputation.
dry, rough skin
Cuts
Mineral-rich chloride, sulfate and sulfur waters have a long-recorded soothing effect on minor cuts and slow-healing skin.
minor wounds
Recovery
Warmth and buoyancy lower stress markers and improve sleep; habitual bathing is linked to lower rates of depression.
fatigue, stress
Take care
Sensitive-skin caution
Strongly acidic or sulfur-rich water can sting broken, atopic-flare, or dry elderly skin. Ease in slowly and rinse off if it stings.
broken or dry skin
From a certificate analyzed in 2018.
- Active stage of any illness (especially with fever), active tuberculosis, advanced malignant tumor, severe anemia or other marked physical weakness
- Severe heart or lung disease causing shortness of breath on slight exertion, severe kidney disease with edema, gastrointestinal bleeding, visible bleeding, acute exacerbation of a chronic illness
- People with sensitive skin or mucous membranes, dry skin in the elderly
Full composition
The bar is each ion's share of charge (mval%) within its group; over 20% names the spring. Gases, silica and trace metals are measured by mass only.
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺578mgP79 national74%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺112mgP76 national16%
- Potassiumminor; matters for drinking limitsK⁺14.6mgP52 national1%
- StrontiumSr²⁺1.8mgP86 national0.1%
- MagnesiumMg²⁺0.50mgP20 national0.1%
- LithiumLi⁺0.70mgP63 national
- BariumBa²⁺0.21mgP73 national
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺0.06mgP17 national
- Manganesetrace; companion to iron springsMn²⁺0.06mgP23 national
- Aluminumshows up in acidic volcanic waterAl³⁺NDmg
- Hydrogenmakes the water acidic — sharp and bactericidalH⁺< —mg
- AmmoniumNH₄⁺NDmg
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻1,248mgP93 national60%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻348mgP78 national21%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻213mgP57 national18%
- FluorideF⁻5.8mgP80 national0.9%
- Hydrogen sulfideHS⁻1.7mgP76 national0.1%
- Iodideyellows in air; helps blood lipidsI⁻1.1mgP81 national
- Bromidetrace, sea-originBr⁻0.50mgP48 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃260mgP95 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂34.7mgP82 national
Measured at the source
On the certificate
From a certificate analyzed in 2018.
- Chronic muscle or joint pain and stiffness (rheumatoid arthritis, osteoarthritis, lower back pain, neuralgia, frozen shoulder, bruises, sprains — chronic phase)
- Cold sensitivity, peripheral circulation disorders, reduced gastrointestinal function (heaviness, bloating)
- Mild hypertension, impaired glucose tolerance (diabetes), mild hypercholesterolemia, mild asthma or emphysema, hemorrhoid pain, autonomic nervous system instability, stress-related symptoms (sleep disorders, depressed mood), convalescence, fatigue recovery, general health improvement
- Cuts, peripheral circulation disorders, cold sensitivity, depressed mood, dry skin, atopic dermatitis, psoriasis vulgaris, chronic eczema, pyoderma
Evidence
- Maeda M. 温泉の医学的効果とその科学的根拠. J. Hot Spring Science 70:197–207, 2021.
- Tei C, Kihara T. Waon Therapy for Chronic Heart Failure. J. Cardiology 53(2):214–218, 2009.
- Coavoy-Sánchez SA et al. Hydrogen sulfide and dermatological diseases. Int. J. Dermatology, 2019.
- Naito Y et al. A Hot-Spring Water Improves Inflammatory Conditions in an Atopic Dermatitis Model. Biomedicines 13(11):2707, 2025.
- Akiyama H et al. Antimicrobial effects of acidic hot-spring water on S. aureus. J. Dermatological Science 24(3):193–200, 2000.
- Toriyama T et al. Carbon dioxide foot bathing on critical limb ischemia. International Angiology 21(4):367–373, 2002.
- Donaubauer AJ et al. Serial radon spa therapy on pain in musculoskeletal disorders. Frontiers in Immunology, 2024.
- Verhagen AP et al. Balneotherapy for rheumatoid arthritis. Cochrane Database of Systematic Reviews CD000518, 2015.
- Li H et al. Bicarbonate Ionized Water Bathing Enhances Natural Killer Cell Activity. Scientific Reports 14:51851, 2024.
- Takeda M et al. Hot spring bathing practices have a positive effect on mental health in Japan. Heliyon 9(9):e19631, 2023.
- Ministry of the Environment, Japan. 禁忌症及び入浴又は飲用上の注意事項 (2014 notice).official