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Susukinohara Ichinoyu

Water profile

Susukinohara Ichinoyu

Spring chemistry and what it does, with the research behind it.

大平台温泉(第3号井戸)Ohiradai Onsen (Well No. 3)

湯Simple

Drawn from Well No. 3 of the Ohiradai source, this is an alkaline simple thermal spring — hot at the wellhead (65 °C) and squarely in the Japanese 'beauty-water' family, with pH 9.2 giving a noticeably slippery feel on the skin. Mineralization is light (775 mg/kg), but a healthy 67.7 mg/kg of metasilicic acid leaves a thin silica film that smooths the skin. Colourless, tasteless and odourless — a clean, well-behaved water.

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

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.

Cationsshare of charge (mval%)
  • Sodium214mgP54 national
  • Calcium30.3mgP46 national
  • Potassium3.4mgP28 national
  • Aluminum0.04mgP26 national
  • Strontium0.03mgP12 national
  • Lithium0.02mgP12 national
  • Barium< —mg
  • FeTotal< —mg
  • Magnesium< —mg
  • Manganese< —mg
Anionsshare of charge (mval%)
  • Chloride232mgP57 national
  • Sulfate187mgP64 national
  • Carbonate24.0mgP75 national
  • Bicarbonate1.2mgP2 national
  • Fluoride0.63mgP38 national
  • Bromide< —mg
  • Hydrogen phosphate< —mg
  • Nitrate< —mg
Non-dissociatedmeasured by mass
  • Metasilicic acid67.7mgP43 national
  • Metaboric acid14.3mgP68 national
Dissolved gasesmeasured by mass
  • Free carbon dioxide< —mg
Trace metalsmeasured by mass
  • Arsenic0.41mgP91 national
  • Copper< —mg
  • Mercury< —mg
  • Lead< —mg

Measured at the source

Source temperature
65.0°C
Hot
Tonicity
0.78g/kg
Hypotonic
Free CO₂
0.10mg/kg
Low

Evidence

  1. 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.
  2. Naito Y et al. A Hot-Spring Water Improves Inflammatory Conditions in an Atopic Dermatitis Model. Biomedicines 13(11):2707, 2025.
  3. Donaubauer AJ et al. Serial radon spa therapy on pain in musculoskeletal disorders. Frontiers in Immunology, 2024.
  4. Verhagen AP et al. Balneotherapy for rheumatoid arthritis. Cochrane Database of Systematic Reviews CD000518, 2015.
  5. Li H et al. Bicarbonate Ionized Water Bathing Enhances Natural Killer Cell Activity. Scientific Reports 14:51851, 2024.
  6. Takeda M et al. Hot spring bathing practices have a positive effect on mental health in Japan. Heliyon 9(9):e19631, 2023.

大涌谷温泉 蒸気造成混合泉2号線(仙石原方面)Owakudani Onsen — Steam-Generated Blend Line No. 2 (Sengokuhara branch)

酸Acidic

A rare steam-generated blended source — volcanic steam from Owakudani is condensed and routed to Sengokuhara through pipeline No. 2. The water is strongly acidic (pH 2.0) with the sharp prickle characteristic of the acidic-spring family, long documented for stubborn skin conditions. It runs hot at the wellhead (64.1 °C) and carries the settled, mineral-rich body of a calcium sulfate-chloride spring, with a generous 120 mg/kg of metasilicic acid layered on top.

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

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.

Cationsshare of charge (mval%)
  • Calcium91.9mgP71 national
  • Sodium36.4mgP8 national
  • Magnesium32.9mgP78 national
  • Aluminum12.4mgP90 national
  • Hydrogen10.1mgP92 national
  • Iron (II)7.7mgP85 national
  • Potassium3.4mgP27 national
  • Manganese1.6mgP88 national
  • Strontium0.05mgP14 national
  • Zinc0.03mgP57 national
Anionsshare of charge (mval%)
  • Sulfate440mgP83 national
  • Chloride236mgP58 national
  • HSO4147mgP79 national
  • Nitrate0.68mgP65 national
  • Fluoride0.12mgP10 national
  • BromideNDmg
Non-dissociatedmeasured by mass
  • Metasilicic acid120mgP61 national
  • Metaboric acid4.2mgP31 national
  • H2SO4Free3.5mgP82 national
Dissolved gasesmeasured by mass
  • Free hydrogen sulfide0.38mgP69 national
Trace metalsmeasured by mass
  • Arsenic0.0070mgP18 national
  • CadmiumNDmg
  • CopperNDmg
  • MercuryNDmg
  • LeadNDmg

Measured at the source

pH
2.00
Acidic
Source temperature
64.1°C
Hot
Tonicity
1.15g/kg
Hypotonic
Free H₂S
0.38mg/kg
Low

Evidence

  1. 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.
  2. Kario K et al. Hemodynamic Effects of Hot Spring Bathing. Hypertension Research 46(3):711–720, 2023.
  3. Tei C, Kihara T. Waon Therapy for Chronic Heart Failure. J. Cardiology 53(2):214–218, 2009.
  4. Coavoy-Sánchez SA et al. Hydrogen sulfide and dermatological diseases. Int. J. Dermatology, 2019.
  5. Naito Y et al. A Hot-Spring Water Improves Inflammatory Conditions in an Atopic Dermatitis Model. Biomedicines 13(11):2707, 2025.
  6. Akiyama H et al. Antimicrobial effects of acidic hot-spring water on S. aureus. J. Dermatological Science 24(3):193–200, 2000.
  7. Toriyama T et al. Carbon dioxide foot bathing on critical limb ischemia. International Angiology 21(4):367–373, 2002.
  8. Donaubauer AJ et al. Serial radon spa therapy on pain in musculoskeletal disorders. Frontiers in Immunology, 2024.
  9. Verhagen AP et al. Balneotherapy for rheumatoid arthritis. Cochrane Database of Systematic Reviews CD000518, 2015.
  10. Li H et al. Bicarbonate Ionized Water Bathing Enhances Natural Killer Cell Activity. Scientific Reports 14:51851, 2024.
  11. Takeda M et al. Hot spring bathing practices have a positive effect on mental health in Japan. Heliyon 9(9):e19631, 2023.
  12. 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

Educational, not medical advice. If you have a health condition, consult a physician before onsen therapy.