Carbon dioxide springs are hot springs that contain a certain amount of carbon dioxide. A distinguishing feature is that fine bubbles may cling to the skin during bathing. They are often called carbonated springs.

A clear point for travelers is that, more than visual spectacle, these springs make it easy to stay longer even in lukewarm water and let you experience the unique bubble effect. It is easier to understand them as an unusual spring type than to expect major medical benefits.

What are carbon dioxide springs

Carbon dioxide springs are a spring type that contains free carbon dioxide in the water. They are generally better known as carbonated springs.

Like the carbonation in soft drinks, carbon dioxide is involved, but the sensation is not as strong as drinking a fizzy beverage. These are springs where you may notice a difference on your skin while bathing.

Why bubbles form

Carbon dioxide dissolved in the water can attach to the skin and appear as fine bubbles. This is an easy-to-recognize characteristic of carbon dioxide springs.

However, the amount and visibility of bubbles vary by individual and by facility. Lack of many bubbles does not necessarily mean the spring is not authentic.

Why baths are often lukewarm

Carbon dioxide springs are often enjoyed at relatively lukewarm temperatures. High temperatures cause the carbon dioxide to escape more easily, so slightly cooler water helps preserve the bubbles and the impression of the spring.

For people who prefer very hot baths, this may feel underwhelming at first. On the other hand, they suit people who want to soak slowly for a longer time.

About the so-called 'heart's bath'

Carbon dioxide springs are sometimes described as a 'heart's bath,' but it is best not to take that phrase as a literal medical claim. It is safer to understand this spring type as one that many people feel warms them easily even at lower temperatures.

People with concerns about their heart or blood pressure should not assume the spring is suitable based on nickname alone and should prioritize reasonable bathing times and checking their condition.

Why they are rare in Japan

Carbon dioxide springs are not very numerous in Japan, so they tend to leave a strong impression among onsen enthusiasts when found. Nagayu Onsen is often cited as a representative example.

If you find a carbon dioxide spring while traveling, think of it as encountering a rare spring type. That said, rarity does not mean it is strongly recommended for everyone.

Difference from artificial carbonated springs

Recently, artificial carbonated springs have become common at facilities such as super sento. The difference from natural carbon dioxide springs is that carbon dioxide is added artificially.

For travelers, it is more practical to check the temperature range and how the water feels than to worry only about whether it is natural or artificial. Natural does not always mean superior, nor does artificial always mean inferior.

Bathing tips

In carbon dioxide springs, you are more likely to notice bubbles and sensations if you enter calmly rather than moving around hastily. Even in lukewarm water, monitor for dizziness or fatigue and bath for a comfortable duration.

Also, just because you can stay in longer does not mean you should overdo it. Even at lower temperatures, excessively long baths can cause tiredness.

Who it suits

These springs suit people who dislike very hot baths, want to soak slowly in lukewarm water, or want to try a rare spring type. The bubble-on-skin effect is an attractive, easy-to-recognize feature.

Conversely, those who want a quick, intense hot sensation may find them lacking. Carbon dioxide springs are a type that emphasizes a relaxed, slow bathing experience rather than pronounced heat.

Summary

Carbon dioxide springs are a rare type of hot spring where fine bubbles may cling to the skin and where you can enjoy soaking slowly in lukewarm water. The visible bubbles make the spring type easy to understand, even for first-timers.

However, do not take expressions like 'heart's bath' as literal efficacy claims. Enjoy these springs within your physical limits and prioritize your condition. For travelers seeking unusual spring types, carbon dioxide springs are likely to be a memorable experience.