What are bicarbonate hot springs? Based on the Environment Ministry standard that the main anion is bicarbonate ion, we explain the differences between sodium bicarbonate springs and calcium-magnesium bicarbonate springs, why they feel smooth, why they are called beauty baths, and why moisturizing after bathing matters. We also clarify how they differ from carbonated springs.
Published: Dec 24, 2025
What are bicarbonate hot springs? Based on the Environment Ministry standard that the main anion is bicarbonate ion, we explain the differences between sodium bicarbonate springs and calcium-magnesium bicarbonate springs, why they feel smooth, why they are called beauty baths, and why moisturizing after bathing matters. We also clarify how they differ from carbonated springs.
Published: Dec 24, 2025
Bicarbonate hot springs are one of the 10 types of therapeutic springs, defined by water whose main anion is bicarbonate ion (HCO₃⁻). Because they often leave the skin feeling slippery and smooth during bathing, they have long been called beauty baths and skin-beauty baths in many places. However, this is only a popular name based on how they feel, and it does not guarantee cosmetic benefits.
In short, the smooth feeling is often explained by the way weakly alkaline water makes old dead skin cells and excess sebum easier to remove. The flip side is that skin may dry out more easily after bathing. In this article, we organize the definition of bicarbonate hot springs, the difference between sodium bicarbonate springs and calcium-magnesium bicarbonate springs, how the smooth sensation works, and the need for moisturizing after a bath, based on the Environment Ministry's standards. For the full picture of all 10 spring types, see the hot spring spring-type guide. Here, we focus only on bicarbonate hot springs.
This article provides general information and does not guarantee any specific cosmetic or health benefits. Skin condition and sensations vary by individual. If you have sensitive skin, concerns about your skin, or are not feeling well, start with a short soak, do not overdo it, and follow the facility's instructions.
Whether a spring is classified as a bicarbonate hot spring depends on what the main dissolved anion is. Under the Environment Ministry's standard, a hot spring with a certain level of dissolved substances and bicarbonate ion (HCO₃⁻) as the main anion is defined as a bicarbonate hot spring. If a bathhouse displays terms such as "bicarbonate hot spring" or "sodium bicarbonate hot spring," the water meets this standard.
One characteristic of bicarbonate hot springs is that they are hard to identify by appearance alone. Unlike the white turbidity of sulfur springs or the reddish-brown color of iron-containing springs, they are often colorless and clear. They also tend to have a mild scent, so it can be difficult to distinguish them from simple hot springs just by looking at the water on site. The difference is more noticeable in the feel of the water than in appearance, and many people only notice the slippery, smooth sensation once they enter.
It is also important to note that the name of a bicarbonate hot spring includes the type of cation associated with the bicarbonate ion. For example, labels such as "sodium bicarbonate hot spring" and "calcium bicarbonate hot spring" show this, and the difference in cation corresponds directly to the traditional names, such as baking soda spring and alkaline earth bicarbonate spring.
Traditionally, bicarbonate hot springs have been divided into two types depending on the cation associated with the bicarbonate ion. You do not need to memorize the chemistry in detail, but knowing the traditional names makes facility labels easier to read.
| Type (current name) | Traditional name | Main cation | Tendency |
|---|---|---|---|
| Sodium bicarbonate hot spring | Baking soda spring | Sodium | Often feels smooth and slippery, and is frequently described as a beauty bath |
| Calcium-magnesium bicarbonate hot spring | Alkaline earth bicarbonate spring | Calcium, magnesium | A gentler bathing feel. Lime-like deposits may appear at the source outlet or in the bath |
In general, the type most often associated with the term beauty bath is the baking soda spring, or sodium bicarbonate hot spring. Alkaline earth bicarbonate springs are based on calcium and magnesium, and are more often described as gentle than as especially smooth. In reality, many springs are mixed types that also contain chloride or sulfate, and they may be displayed under long names such as "sodium bicarbonate and chloride spring." As a traveler, it is easiest to first check whether bicarbonate is the main component, then look at which cation is dominant to understand the bathing feel.
Bicarbonate hot springs have long been called beauty baths because many people feel that the skin becomes smoother after bathing. In weakly alkaline water, old dead skin cells and excess sebum on the surface may be emulsified and removed more easily, which is said to create the slippery, smooth sensation.
That said, this is only a description of a change in feel, not a medical claim of strong cosmetic effects. The smooth sensation is also related to pH, meaning the level of acidity or alkalinity of the water, so even among bicarbonate hot springs, the experience can vary depending on the water quality. For a general explanation of the relationship between pH and skin feel, see the hot spring pH guide.
It is also worth noting that bicarbonate hot springs are not the only waters called beauty baths. If we compare the spring types often said to make the skin smooth, the differences in the underlying mechanisms become clearer.
| Spring type | Main reason it is said to feel smooth | Note |
|---|---|---|
| Bicarbonate hot spring | Weak alkalinity makes dead skin cells and sebum easier to emulsify and remove | This is especially true of baking soda springs. Skin may dry out after bathing |
| Alkaline simple hot spring | High pH creates a smooth, soft skin feel | Dissolved minerals do not meet the standard, and the water is mild |
| Sulfur spring | Distinct feel due to its components. Strong character in color and scent | It is discussed more for its color and smell than for smoothness |
As you can see, beauty bath is not a single spring type, and the reason for the smooth feel differs by spring. In the case of bicarbonate hot springs, the main explanation is the removal of dead skin cells and sebum due to weak alkalinity.
Because the names are similar, they are often confused, but bicarbonate hot springs and carbonated springs are completely different. Bicarbonate hot springs are classified because bicarbonate ion (HCO₃⁻) dissolved in the water is the main anion. Carbonated springs, on the other hand, contain a certain amount or more of free carbon dioxide (CO₂) dissolved in the water, and small bubbles cling to the body during bathing.
In other words, one is bicarbonate dissolved as an ion, while the other is carbon dioxide dissolved as a gas, so the bathing feel and body sensation are completely different. Bicarbonate hot springs are associated with smoothness, while carbonated springs are associated with bubbles and circulation-related topics. For more on carbonated springs themselves, see What is a carbonated spring?. By checking the spring name on the label or hot spring analysis report, you can avoid confusing the two.
One especially important point about bicarbonate hot springs is that skin may dry out more easily after bathing. The smooth feeling is linked to the easier removal of dead skin cells and sebum, but that also means the oils that protect the skin surface may be lost more easily. Even if your skin feels smooth right after bathing, some people later notice tightness or dryness.
For that reason, it is better not to stop at the pleasant skin feel, but to think about moisturizing after the bath. After soaking, avoid rubbing with a towel and instead gently press away moisture, then moisturize to reduce stress on the skin. This is especially important for people with dry skin or for those who soaked for a long time. If you treat the hot spring experience as more than just the soak itself and include post-bath care, you can enjoy the smooth feeling more comfortably.
Avoiding long soaks is also practical. When the water feels smooth, you may want to stay in longer, but that can lead to dizziness or dryness, so shorter sessions with breaks are better. If you have sensitive skin, slipperiness does not necessarily mean the water suits you, so it is safer to start with a short soak and decide how to bathe after observing your skin's reaction.
Bicarbonate hot springs are also one of the spring types for which the Environment Ministry guidelines generally list bathing and drinking indications. For bathing, dry skin is sometimes mentioned, but these indications are based on repeated use over a period of time and do not guarantee effects from a single bath. Individual differences are large, and this article does not claim any benefits.
The same attitude should be applied to the term beauty bath. It is a widely used popular name, not a promise that everyone's skin will become beautiful. If expectations are raised too much, they can easily diverge from the actual experience. More slipperiness does not automatically mean higher quality, and the appeal of a hot spring is not determined by one sensation alone. If you choose while considering the spring quality, temperature, scenery, ease of staying, and how the water is used, you are more likely to enjoy it beyond just the skin feel. If you also want to appreciate whether the source water is fresh and whether it is diluted or heated, see What is gensen kakenagashi?.
Because this is a gentle spring type, it can feel underwhelming if you expect strong stimulation or a distinctive color. In that case, comparing it with sulfate hot springs, which have more character in appearance and the way they warm you, can actually make the smoothness of bicarbonate hot springs easier to understand.
Yes. They are different spring types. Bicarbonate hot springs are classified because bicarbonate ion (HCO₃⁻) is the main anion dissolved in the water. Carbonated springs contain a certain amount or more of free carbon dioxide (CO₂), and their hallmark is that small bubbles cling to the body during bathing. If you think of bicarbonate hot springs as the ones discussed for smoothness and carbonated springs as the ones known for bubbles, it is easier to avoid confusion.
Beauty bath is a popular name based on the smooth feel of the skin, not a term that guarantees cosmetic effects. It is sometimes explained that weakly alkaline water makes old dead skin cells and sebum easier to remove, creating a smoother sensation, but individual experiences vary, and this article does not claim any effects. It is best to enjoy the bath without expecting too much and while observing how your skin feels and how it looks afterward.
The same property that makes dead skin cells and sebum easier to remove can also mean that the oils protecting the skin surface are lost more easily. For that reason, even if your skin feels smooth right after bathing, some people later feel tightness or dryness. Gently drying off moisture and moisturizing after the bath can help reduce the burden on the skin.
Both are bicarbonate hot springs, but the associated cations are different. Baking soda spring is the traditional name for sodium bicarbonate hot spring, and it is the type more likely to feel smooth and slippery and to be described as a beauty bath. Alkaline earth bicarbonate spring is based on calcium and magnesium, has a gentler bathing feel, and may show lime-like deposits at the source outlet or in the bathtub.
It is difficult. Bicarbonate hot springs are often colorless and clear with a mild scent, so they are not easy to distinguish from simple hot springs by appearance alone. The difference is more likely to show up in the feel of the water, and if you want to know for sure, the most reliable method is to check the hot spring analysis report posted in the dressing room or bath area.
Bicarbonate hot springs are therapeutic springs whose main anion is bicarbonate ion (HCO₃⁻), and they have long been called beauty baths in many places because of their smooth skin feel. Depending on the associated cation, they are divided into sodium bicarbonate hot springs, or baking soda springs, and calcium-magnesium bicarbonate hot springs, or alkaline earth bicarbonate springs. They are often colorless and clear, so the appearance is gentle, and the difference tends to show up in the skin feel.
As a traveler, it is enough to know that the smooth feeling is often explained by the removal of dead skin cells and sebum due to weak alkalinity, that the flip side is that the skin can dry out more easily after bathing, and that they are different from carbonated springs containing free carbon dioxide. Rather than being swayed by the phrase beauty bath alone, the basic approach is to avoid long soaks and include moisturizing after the bath. For the overall picture of each spring type, see the hot spring spring-type guide.
Bicarbonate hot springs are one of the 10 types of therapeutic springs, defined by water whose main anion is bicarbonate ion (HCO₃⁻). Because they often leave the skin feeling slippery and smooth during bathing, they have long been called beauty baths and skin-beauty baths in many places. However, this is only a popular name based on how they feel, and it does not guarantee cosmetic benefits.
In short, the smooth feeling is often explained by the way weakly alkaline water makes old dead skin cells and excess sebum easier to remove. The flip side is that skin may dry out more easily after bathing. In this article, we organize the definition of bicarbonate hot springs, the difference between sodium bicarbonate springs and calcium-magnesium bicarbonate springs, how the smooth sensation works, and the need for moisturizing after a bath, based on the Environment Ministry's standards. For the full picture of all 10 spring types, see the hot spring spring-type guide. Here, we focus only on bicarbonate hot springs.
This article provides general information and does not guarantee any specific cosmetic or health benefits. Skin condition and sensations vary by individual. If you have sensitive skin, concerns about your skin, or are not feeling well, start with a short soak, do not overdo it, and follow the facility's instructions.
Whether a spring is classified as a bicarbonate hot spring depends on what the main dissolved anion is. Under the Environment Ministry's standard, a hot spring with a certain level of dissolved substances and bicarbonate ion (HCO₃⁻) as the main anion is defined as a bicarbonate hot spring. If a bathhouse displays terms such as "bicarbonate hot spring" or "sodium bicarbonate hot spring," the water meets this standard.
One characteristic of bicarbonate hot springs is that they are hard to identify by appearance alone. Unlike the white turbidity of sulfur springs or the reddish-brown color of iron-containing springs, they are often colorless and clear. They also tend to have a mild scent, so it can be difficult to distinguish them from simple hot springs just by looking at the water on site. The difference is more noticeable in the feel of the water than in appearance, and many people only notice the slippery, smooth sensation once they enter.
It is also important to note that the name of a bicarbonate hot spring includes the type of cation associated with the bicarbonate ion. For example, labels such as "sodium bicarbonate hot spring" and "calcium bicarbonate hot spring" show this, and the difference in cation corresponds directly to the traditional names, such as baking soda spring and alkaline earth bicarbonate spring.
Traditionally, bicarbonate hot springs have been divided into two types depending on the cation associated with the bicarbonate ion. You do not need to memorize the chemistry in detail, but knowing the traditional names makes facility labels easier to read.
| Type (current name) | Traditional name | Main cation | Tendency |
|---|---|---|---|
| Sodium bicarbonate hot spring | Baking soda spring | Sodium | Often feels smooth and slippery, and is frequently described as a beauty bath |
| Calcium-magnesium bicarbonate hot spring | Alkaline earth bicarbonate spring | Calcium, magnesium | A gentler bathing feel. Lime-like deposits may appear at the source outlet or in the bath |
In general, the type most often associated with the term beauty bath is the baking soda spring, or sodium bicarbonate hot spring. Alkaline earth bicarbonate springs are based on calcium and magnesium, and are more often described as gentle than as especially smooth. In reality, many springs are mixed types that also contain chloride or sulfate, and they may be displayed under long names such as "sodium bicarbonate and chloride spring." As a traveler, it is easiest to first check whether bicarbonate is the main component, then look at which cation is dominant to understand the bathing feel.
Bicarbonate hot springs have long been called beauty baths because many people feel that the skin becomes smoother after bathing. In weakly alkaline water, old dead skin cells and excess sebum on the surface may be emulsified and removed more easily, which is said to create the slippery, smooth sensation.
That said, this is only a description of a change in feel, not a medical claim of strong cosmetic effects. The smooth sensation is also related to pH, meaning the level of acidity or alkalinity of the water, so even among bicarbonate hot springs, the experience can vary depending on the water quality. For a general explanation of the relationship between pH and skin feel, see the hot spring pH guide.
It is also worth noting that bicarbonate hot springs are not the only waters called beauty baths. If we compare the spring types often said to make the skin smooth, the differences in the underlying mechanisms become clearer.
| Spring type | Main reason it is said to feel smooth | Note |
|---|---|---|
| Bicarbonate hot spring | Weak alkalinity makes dead skin cells and sebum easier to emulsify and remove | This is especially true of baking soda springs. Skin may dry out after bathing |
| Alkaline simple hot spring | High pH creates a smooth, soft skin feel | Dissolved minerals do not meet the standard, and the water is mild |
| Sulfur spring | Distinct feel due to its components. Strong character in color and scent | It is discussed more for its color and smell than for smoothness |
As you can see, beauty bath is not a single spring type, and the reason for the smooth feel differs by spring. In the case of bicarbonate hot springs, the main explanation is the removal of dead skin cells and sebum due to weak alkalinity.
Because the names are similar, they are often confused, but bicarbonate hot springs and carbonated springs are completely different. Bicarbonate hot springs are classified because bicarbonate ion (HCO₃⁻) dissolved in the water is the main anion. Carbonated springs, on the other hand, contain a certain amount or more of free carbon dioxide (CO₂) dissolved in the water, and small bubbles cling to the body during bathing.
In other words, one is bicarbonate dissolved as an ion, while the other is carbon dioxide dissolved as a gas, so the bathing feel and body sensation are completely different. Bicarbonate hot springs are associated with smoothness, while carbonated springs are associated with bubbles and circulation-related topics. For more on carbonated springs themselves, see What is a carbonated spring?. By checking the spring name on the label or hot spring analysis report, you can avoid confusing the two.
One especially important point about bicarbonate hot springs is that skin may dry out more easily after bathing. The smooth feeling is linked to the easier removal of dead skin cells and sebum, but that also means the oils that protect the skin surface may be lost more easily. Even if your skin feels smooth right after bathing, some people later notice tightness or dryness.
For that reason, it is better not to stop at the pleasant skin feel, but to think about moisturizing after the bath. After soaking, avoid rubbing with a towel and instead gently press away moisture, then moisturize to reduce stress on the skin. This is especially important for people with dry skin or for those who soaked for a long time. If you treat the hot spring experience as more than just the soak itself and include post-bath care, you can enjoy the smooth feeling more comfortably.
Avoiding long soaks is also practical. When the water feels smooth, you may want to stay in longer, but that can lead to dizziness or dryness, so shorter sessions with breaks are better. If you have sensitive skin, slipperiness does not necessarily mean the water suits you, so it is safer to start with a short soak and decide how to bathe after observing your skin's reaction.
Bicarbonate hot springs are also one of the spring types for which the Environment Ministry guidelines generally list bathing and drinking indications. For bathing, dry skin is sometimes mentioned, but these indications are based on repeated use over a period of time and do not guarantee effects from a single bath. Individual differences are large, and this article does not claim any benefits.
The same attitude should be applied to the term beauty bath. It is a widely used popular name, not a promise that everyone's skin will become beautiful. If expectations are raised too much, they can easily diverge from the actual experience. More slipperiness does not automatically mean higher quality, and the appeal of a hot spring is not determined by one sensation alone. If you choose while considering the spring quality, temperature, scenery, ease of staying, and how the water is used, you are more likely to enjoy it beyond just the skin feel. If you also want to appreciate whether the source water is fresh and whether it is diluted or heated, see What is gensen kakenagashi?.
Because this is a gentle spring type, it can feel underwhelming if you expect strong stimulation or a distinctive color. In that case, comparing it with sulfate hot springs, which have more character in appearance and the way they warm you, can actually make the smoothness of bicarbonate hot springs easier to understand.
Yes. They are different spring types. Bicarbonate hot springs are classified because bicarbonate ion (HCO₃⁻) is the main anion dissolved in the water. Carbonated springs contain a certain amount or more of free carbon dioxide (CO₂), and their hallmark is that small bubbles cling to the body during bathing. If you think of bicarbonate hot springs as the ones discussed for smoothness and carbonated springs as the ones known for bubbles, it is easier to avoid confusion.
Beauty bath is a popular name based on the smooth feel of the skin, not a term that guarantees cosmetic effects. It is sometimes explained that weakly alkaline water makes old dead skin cells and sebum easier to remove, creating a smoother sensation, but individual experiences vary, and this article does not claim any effects. It is best to enjoy the bath without expecting too much and while observing how your skin feels and how it looks afterward.
The same property that makes dead skin cells and sebum easier to remove can also mean that the oils protecting the skin surface are lost more easily. For that reason, even if your skin feels smooth right after bathing, some people later feel tightness or dryness. Gently drying off moisture and moisturizing after the bath can help reduce the burden on the skin.
Both are bicarbonate hot springs, but the associated cations are different. Baking soda spring is the traditional name for sodium bicarbonate hot spring, and it is the type more likely to feel smooth and slippery and to be described as a beauty bath. Alkaline earth bicarbonate spring is based on calcium and magnesium, has a gentler bathing feel, and may show lime-like deposits at the source outlet or in the bathtub.
It is difficult. Bicarbonate hot springs are often colorless and clear with a mild scent, so they are not easy to distinguish from simple hot springs by appearance alone. The difference is more likely to show up in the feel of the water, and if you want to know for sure, the most reliable method is to check the hot spring analysis report posted in the dressing room or bath area.
Bicarbonate hot springs are therapeutic springs whose main anion is bicarbonate ion (HCO₃⁻), and they have long been called beauty baths in many places because of their smooth skin feel. Depending on the associated cation, they are divided into sodium bicarbonate hot springs, or baking soda springs, and calcium-magnesium bicarbonate hot springs, or alkaline earth bicarbonate springs. They are often colorless and clear, so the appearance is gentle, and the difference tends to show up in the skin feel.
As a traveler, it is enough to know that the smooth feeling is often explained by the removal of dead skin cells and sebum due to weak alkalinity, that the flip side is that the skin can dry out more easily after bathing, and that they are different from carbonated springs containing free carbon dioxide. Rather than being swayed by the phrase beauty bath alone, the basic approach is to avoid long soaks and include moisturizing after the bath. For the overall picture of each spring type, see the hot spring spring-type guide.