武雄温泉第5号源泉Takeo Onsen Spring No. 5
A sodium-led alkaline simple thermal spring, hot at the wellhead (44.5 C). The chemistry leans on bicarbonate with a modest chloride and carbonate edge, giving the slippery, soft feel of Japan's beauty-water family. Mineralization is light at 713 mg/kg, so the water sits gently on the skin rather than coating it.
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
From a certificate analyzed in 2022.
- 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
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⁺193mgP50 national
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺2.3mgP8 national
- Potassiumminor; matters for drinking limitsK⁺2.0mgP22 national
- LithiumLi⁺0.40mgP46 national
- Magnesiummild; a laxative if you drink itMg²⁺0.20mgP14 national
- AmmoniumNH₄⁺0.10mgP23 national
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻360mgP68 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻74.8mgP32 national
- Carbonatestrongly alkaline; slippery feelCO₃²⁻16.2mgP59 national
- Fluoridetrace; drinking limits applyF⁻4.7mgP76 national
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻1.9mgP10 national
- NitrateNO₃⁻0.40mgP55 national
- Bromidetrace, sea-originBr⁻0.20mgP28 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃48.8mgP27 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂9.0mgP52 national
Measured at the source
On the certificate
From a certificate analyzed in 2022.
- Chronic muscle or joint pain or stiffness (the chronic phase of rheumatoid arthritis, osteoarthritis, lower back pain, neuralgia, frozen shoulder, bruises, sprains and the like)
- Muscle stiffness associated with motor paralysis
- 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
- Convalescence
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.