A hot (67.8 °C) blended sulfur-bearing sodium sulfate-chloride-bicarbonate spring drawing from Naruko's #2 and #3 wells. Mildly alkaline yet sulfide-rich — the characteristic rotten-egg note of H₂S sits over a moderately mineralized body (1,910 mg/kg). One of Japan's hotter natural sources, mixed before delivery to the bathhouse.
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
Warming
Salt forms a film on the skin that slows heat loss, so the warmth lingers long after the bath (the classic heat-keeping water, nettō 熱の湯).
cold sensitivity
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
- 病気の活動期(特に熱のあるとき)、活動性の結核、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、少し動くと息苦しくなるような重い心肺疾患、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
- 皮膚・粘膜の過敏な人、高齢者の皮膚乾燥症
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⁺449mgP74 national91%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺90.1mgP68 national
- Potassiumminor; matters for drinking limitsK⁺31.1mgP75 national
- Magnesiummild; a laxative if you drink itMg²⁺2.6mgP37 national
- LithiumLi⁺2.0mgP91 national
- Iron (II)rusts brown in air; iron for anemia when drinkableFe²⁺< —mg
- Hydrogenmakes the water acidic — sharp and bactericidalH⁺< —mg
- Manganesetrace; companion to iron springsMn²⁺< —mg
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻471mgP86 national38%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻299mgP63 national28%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻346mgP68 national7%
- Hydrogen sulfidesulfur character — antibacterialHS⁻35.7mgP100 national4%
- Fluoridetrace; drinking limits applyF⁻—mg
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃132mgP65 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S4.7mgP85 national
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(関節リウマチ・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)、運動麻痺における筋肉のこわばり、冷え性、末梢循環障害、胃腸機能の低下(胃もたれなど、軽症のものに限る)、軽症高血圧、耐糖能異常(糖尿病)、軽い高コレステロール血症、軽い喘息又は肺気腫、痔の痛み、自律神経不安定症・ストレスによる諸症状(睡眠障害、うつ状態など)、病後回復期
- アトピー性皮膚炎、尋常性乾癬、慢性湿疹、表皮化膿症、きりきず、軽症の末梢循環障害、冷え性、皮膚乾燥症、うつ状態
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.
- Kario K et al. Hemodynamic Effects of Hot Spring Bathing. Hypertension Research 46(3):711–720, 2023.
- 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