A sulfur spring of the Shirahone Onsen area — a calcium-magnesium bicarbonate-chloride water of the hydrogen-sulfide type. It carries free H₂S and bisulfide with the characteristic rotten-egg note, the kind of sulfur water famous for turning milky-white once it meets the air. Neutral in pH and moderately mineralized at 1,108 mg/kg dissolved solids, it has noticeable body. The source is also one of the rarer ones approved for drinking, with the certificate listing benefits for gastroduodenal ulcers and high cholesterol.
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
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
Gut & metabolic
Bicarbonate and sulfate waters, taken as a drink, neutralize stomach acid and help with constipation and gout.
stomach, gout (drinking)
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
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.
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺170mgP83 national
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺44.3mgP11 national
- Magnesiummild; a laxative if you drink itMg²⁺38.0mgP82 national
- Potassiumminor; matters for drinking limitsK⁺14.3mgP52 national
- AmmoniumNH₄⁺1.6mgP76 national
- BariumBa²⁺0.40mgP81 national
- StrontiumSr²⁺0.40mgP62 national
- LithiumLi⁺0.30mgP44 national
- Manganesetrace; companion to iron springsMn²⁺0.30mgP53 national
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻741mgP84 national
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻47.2mgP27 national
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻12.3mgP24 national
- Hydrogen sulfidesulfur character — antibacterialHS⁻1.3mgP72 national
- Fluoridetrace; drinking limits applyF⁻0.30mgP24 national
- Thiosulfateoxidized sulfurS₂O₃²⁻0.30mgP58 national
- Bromidetrace, sea-originBr⁻0.10mgP15 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃32.8mgP15 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂4.0mgP30 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂300mgP93 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S4.7mgP85 national
- ArsenicAs0.0010mgP6 national
- CadmiumCdNDmg
- ChromiumCrNDmg
- Mercurytoxic trace — part of the drinking-safety checkHgNDmg
- LeadPbNDmg
Measured at the source
On the certificate
- gastric and duodenal ulcers
- reflux esophagitis
- impaired glucose tolerance (diabetes)
- 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.
- 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.
- Li H et al. Bicarbonate Ionized Water Bathing Enhances Natural Killer Cell Activity. Scientific Reports 14:51851, 2024.
- Matsumoto S et al. Hot spring bathing and HbA1c in type 2 diabetes. J. JAPMC 73(3):163–170, 2010.
- 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