What is a Bicarbonate Spring?
A bicarbonate spring has hydrogen carbonate ions (HCO₃⁻) as its dominant anion — the same compound as household baking soda, earning it the nickname "baking-soda spring" (重曹泉).
When you bathe, the bicarbonate softens the stratum corneum and washes away dead skin cells and sebum like a gentle soap, leaving your skin noticeably smoother. This skin-refining quality has earned it the title "the beauty waters" (美人の湯) across Japan.
Indications for Bathing
- CutsThe weak alkalinity of bicarbonate springs helps to suppress bacterial growth on the skin's surface. This gentle cleansing action can keep minor cuts and scrapes clean, providing a soothing effect on the affected area.
- Peripheral circulatory failureBathing in these warm mineral waters is recognized as beneficial for this condition under Japan's official spring quality guidelines. The thermal effects of the bath can help improve blood flow, particularly to the body's extremities.
- Excessive sensitivity to coldAs with other hot springs, the simple act of soaking in warm water raises the body's core temperature and improves circulation. This can provide temporary relief and a lasting feeling of warmth for those who are often cold.
- Xeroderma (dry skin)The bicarbonate ions in the water act as a natural soap, gently softening and removing old, dead skin cells. This process helps to leave the skin feeling smooth and moisturized, which is why these springs are often called "waters of beauty".
Indications for Drinking
- Gastroduodenal ulcerationsDrinking these waters may help neutralize excess stomach acid. The bicarbonate acts as a natural antacid, which can help protect the mucous membranes of the stomach and duodenum from irritation.
- Reflux esophagitisThe bicarbonate content can help neutralize stomach acid that flows back into the esophagus. This action may alleviate the irritation and discomfort associated with acid reflux.
- Impaired glucose tolerance (diabetes)Drinking this spring water is believed to stimulate certain digestive hormones. This process may in turn help improve glucose metabolism, offering potential benefits for managing blood sugar levels.
- Hyperuricemia (gout)The water helps make urine more alkaline, which promotes the excretion of uric acid from the body. This action may help in the management of conditions like gout by reducing uric acid buildup.
How to Bathe in a Bicarbonate Spring
- Bicarbonate strips oils efficiently, so moisturize after bathing if your skin feels dry.Bicarbonate springs have a soap-like effect, breaking down and washing away excess sebum and old skin cells. While this cleansing action is what leaves the skin feeling smooth, it can also strip natural oils. If your skin feels tight or dry after bathing, be sure to apply a moisturizer.
- Pat skin dry without rinsing to keep the beneficial components on your body.The beneficial components of the onsen water, primarily bicarbonate ions, provide a gentle cleansing and skin-softening effect. Rinsing with fresh tap water after your bath would wash these minerals away. Gently patting your skin dry allows these components to remain, prolonging their mild effects.
- For beauty purposes, two 10–15 minute baths work better than one long soak — over-bathing can strip too much keratin.The spring's beautifying effect comes from its ability to soften the skin's outer keratin layer. However, soaking for too long can be overly aggressive, stripping away too much of this protective layer and causing dryness. Shorter, repeated dips are a gentler way to achieve the skin-smoothing benefits.
Recommended Onsen Sequence
Bicarbonate spring → sulphur spring → chloride spring: the bicarbonate removes old keratin, the sulphur boosts circulation, and the chloride seals in moisture — the classic beauty onsen tour.
Related Onsen Facilities
References
Famous Onsen Areas with Carbonated Spring
Check access and tourist information on each onsen area column
Related Articles






















