Kisuke no Yu rises in central Matsuyama as a lightly mineralized simple thermal water that qualifies as a weak radon spring — the kind of source the "hormesis" tradition is built on. It is alkaline enough to carry the slippery beauty-water feel, gentle on the body thanks to a low dissolved load, and holds enough metasilicic acid to leave skin noticeably smooth. The posted analysis puts radon at 182.7 Bq/kg, and the certificate's indications track that chemistry: gout and hyperuricemia, rheumatoid arthritis and ankylosing spondylitis, alongside insomnia and depressed mood.
Good for
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
Recovery
Warmth and buoyancy lower stress markers and improve sleep; habitual bathing is linked to lower rates of depression.
fatigue, stress
Take care
- Active stage of any illness (especially with fever)
- Marked physical debilitation such as active tuberculosis, advanced malignant tumor, or severe anemia
- Severe heart or lung disease causing breathlessness on slight exertion
- Severe kidney disease with edema
- Gastrointestinal bleeding
- Visible bleeding
- Acute exacerbation of a chronic illness
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⁺99.8mgP28 national97%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺2.0mgP7 national2%
- AluminumAl³⁺0.20mgP64 national0.5%
- PotassiumK⁺0.50mgP5 national0.2%
- LithiumLi⁺0.10mgP28 national0.2%
- BariumBa²⁺< —mg
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺< —mg
- Iron (III)Fe³⁺< —mg
- Magnesiummild; a laxative if you drink itMg²⁺< —mg
- Manganesetrace; companion to iron springsMn²⁺< —mg
- AmmoniumNH₄⁺< —mg
- StrontiumSr²⁺< —mg
- ZincZn²⁺< —mg
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻58.3mgP29 national37%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻64.4mgP35 national24%
- Fluoridetrace; drinking limits applyF⁻20.0mgP98 national24%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻10.4mgP52 national8%
- BO2BO₂⁻10.0mgP91 national5%
- SulfateSO₄²⁻0.90mgP7 national0.5%
- Hydrogen sulfideHS⁻0.70mgP60 national0.5%
- HydroxideOH⁻0.40mgP76 national0.5%
- BromideBr⁻0.20mgP29 national0.0%
- Iodideyellows in air; helps blood lipidsI⁻< —mg
- NitrateNO₃⁻< —mg
- Thiosulfateoxidized sulfurS₂O₃²⁻< —mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃51.2mgP29 national
- ArsenicAs< —mg
- CadmiumCd< —mg
- ChromiumCr< —mg
- CopperCu< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —mg
Measured at the source
On the certificate
- 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
- Stress-related symptoms (sleep disorders, depressed mood)
- Hyperuricemia (gout)
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.
- Naito Y et al. A Hot-Spring Water Improves Inflammatory Conditions in an Atopic Dermatitis Model. Biomedicines 13(11):2707, 2025.
- 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.