Hōkōbō Spring is a radon-bearing, weakly radioactive simple thermal water (hypotonic, alkaline, low-temperature). Mineralization is light at 224.5 mg/kg — gentle on the body — and the pH of 8.7 puts it squarely in Japan's alkaline beauty-water family with a slippery feel on the skin. At the source the water is colorless and clear with a faint rotten-egg note from hydrogen sulfide, and radon at 144 Bq/kg places it in the so-called hormesis tradition.
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
- 病気の活動期(特に熱のあるとき)
- Active tuberculosis
- 進行した悪性腫瘍又は高度の貧血など身体衰弱の著しい場合
- 少し動くと息切れをするような重い心臓又は肺の病気
- むくみのあるような重い腎臓の病気
- 消化管出血
- 目に見える出血があるとき
- 慢性の病気の急性増悪期
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⁺53.8mgP15 national77%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺10.0mgP26 national17%
- Magnesiummild; a laxative if you drink itMg²⁺1.6mgP30 national4%
- Potassiumminor; matters for drinking limitsK⁺2.1mgP23 national2%
- CopperCu²⁺< —mg
- ZincZn²⁺< —mg
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻44.1mgP26 national40%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻72.7mgP36 national38%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻14.5mgP27 national10%
- Carbonatestrongly alkaline; slippery feelCO₃²⁻7.2mgP43 national8%
- Fluoridetrace; drinking limits applyF⁻2.4mgP62 national4%
- Hydrogen sulfidesulfur character — antibacterialHS⁻1.1mgP71 national1%
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃9.6mgP2 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂5.4mgP39 national
- ArsenicAs< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —mg
Measured at the source
On the certificate
- 筋肉又は関節の慢性的な痛み又はこわばり(変形性関節症、腰痛症、神経痛、五十肩、打撲、捻挫などの慢性期)
- 冷え症
- Peripheral circulation disorders
- 胃腸機能の低下(胃にガスがたまる感じ)
- Mild hypertension
- Impaired glucose tolerance (diabetes)
- 軽度の高コレステロール血症
- Mild asthma or emphysema
- Hemorrhoid pain
- 高血圧症(浴用)
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.