When asked whether hot springs have health benefits, the honest answer is that we cannot say they have no basis at all, but we also cannot say they cure every ailment. Hot springs affect the body through thermal warmth that raises body temperature, physical forces in water such as hydrostatic pressure and buoyancy, chemical effects from dissolved minerals, and the impact of simply staying in a hot spring area. These are all things that can be explained as facts.

That said, the conclusion should come first: the existence of these effects is not the same as being able to claim that hot springs cure disease. This article is an overview of how to understand the health benefits of hot springs scientifically. It explains the mechanisms behind the three types of effects, how to read the Ministry of the Environment’s public framework of therapeutic springs and indications, and the limits of the evidence, while avoiding overstatement and keeping a neutral tone. Individual topics such as respiratory conditions, toji, bathing frequency, and contraindications will be covered in separate articles.

This article provides general information and is not medical advice. The effects and indications introduced here may not be established, and they are not a substitute for medical care. If you have a chronic condition, are under treatment, or are not feeling well, do not rely on hot springs by yourself; consult your regular doctor if necessary. If your doctor has restricted bathing, their instructions take priority.

Thinking About Hot Spring Health Benefits Separately

Summing up the effects of hot springs in one word, such as “benefits,” can easily lead to misunderstandings. In technical terms, the effects of hot springs and bathing are considered in terms of physical effects such as thermal warmth, water pressure, and buoyancy, chemical effects from dissolved minerals, and travel effects that arise from changes in the environment and daily rhythm when staying in a hot spring area. Rather than explaining health benefits only by the mineral composition of the spring, it is more accurate to view them as the sum of bathing as an activity and time spent in the hot spring area.

The table below organizes each effect and what it is thought to produce. Each is easy to explain through direct experience, but as noted later, that does not mean it cures disease.

The differences between spring qualities based on minerals and chemical effects are covered in detail in The Hot Spring Water Type Guide. The key point here is that hot spring effects are not only about the minerals; they are the combined result of thermal warmth, water pressure, buoyancy, and the restorative effect of staying in the hot spring area.

What Can Be Said Fairly Safely, and What Should Not Be Overstated

From these effects, it is fairly safe to say that warming the body can make stiffness and coldness in muscles and joints feel easier, that some people feel calmer after bathing, that some fall asleep more easily, and that fatigue may feel lighter. Buoyancy reducing the strain on joints and making movement feel easier also matches both theory and experience. These are effects that many people can readily notice and that are relatively easy to explain.

On the other hand, some claims should be avoided. Strong statements such as immunity definitely improves, disease is cured, or blood pressure and blood sugar clearly improve should be treated cautiously. There are studies on hot springs and heat therapy, but the subjects and conditions are often limited, and generalizing too far can create misunderstandings. Especially when someone has a chronic illness or is under treatment, hot springs may support rest and comfort, but they are not a substitute for medical care. Decisions must be made according to symptoms and treatment plans. People and situations to avoid are summarized in Hot Spring Precautions.

How to Read the Ministry of the Environment’s “Therapeutic Springs and Indications”

The “indications” often mentioned as hot spring benefits are a public framework established by the Ministry of the Environment under the Hot Spring Act. Reading this correctly is the key to understanding health benefits scientifically.

First, springs that meet certain standards are designated as “therapeutic springs,” and only therapeutic springs are assigned indications, meaning symptoms or conditions for which their use is considered suitable. There are general indications common to all therapeutic springs and spring-quality-specific indications set according to the spring type. It is important to note that general indications are not claims about the effectiveness of a specific mineral, but general descriptions based mainly on physical effects such as thermal warmth. General indications for bathing include chronic muscle and joint pain and stiffness, sensitivity to cold, peripheral circulation disorders, autonomic instability, stress-related symptoms such as sleep disorders and depressive states, recovery after illness, fatigue recovery, and health promotion.

There are three things that must not be misunderstood here:

• Repeated use over a certain period is assumed. Therapeutic spring indications are not based on the idea that one bath will be enough. They are intended for repeated use over a certain period. The underlying idea is that about 2 to 3 weeks of therapy is usually appropriate for sufficient benefit.
• They do not guarantee effectiveness. Hot spring therapy is a framework aimed more at easing symptoms and discomfort and supporting recovery and health promotion than at curing a specific disease. It does not promise a cure.
• Individual differences are large. Even with the same spring quality and the same way of bathing, the way a person feels and responds varies depending on their constitution and condition.

This idea of “repeating over a certain period” overlaps with the traditional way of using hot springs by staying in a hot spring area to recover, namely toji. As for respiratory conditions, the fact that “mild asthma or emphysema” appears in the general indications is discussed in Hot Springs and the Respiratory System.

Being Honest About the Limits of the Evidence

Even if there is a framework of indications, that does not mean everything is backed by strong scientific evidence. Research on hot spring health benefits includes observational studies and small trials, and the certainty varies. “There is an association” is different from “the hot spring caused it,” and it is too far to treat the former as proof of the latter.

For example, there are reports that staying in a hot spring area for several days or more may make physical condition and test values easier to regulate. But that involves not only bathing, but also factors such as stepping away from work, walking more, and being able to sleep better, meaning travel effects and lifestyle changes are acting at the same time. If the effect is attributed only to the spring minerals, the reality is misunderstood. It is more realistic to view hot spring health benefits as a comprehensive result of multiple overlapping factors.

In practical terms, rather than chasing the strength of the benefits, it makes more sense to choose a bathing style that is not overdone. Recommended bathing times and frequency are summarized in How Long and How Often to Bathe in Hot Springs.

Frequently Asked Questions

Can hot springs cure disease?

We cannot say that they cure disease. Hot springs have effects such as thermal warmth, hydrostatic pressure, buoyancy, minerals, and travel effects, but the Ministry of the Environment’s therapeutic spring framework assumes repeated use over a certain period and does not guarantee effectiveness. Individual differences are also large, and if you are under treatment, hot springs are not a substitute for medical care.

If there is an “indication,” is the effect certain?

No, it is not certain. General indications are mainly general descriptions based on physical effects such as thermal warmth, and they are usually considered on the assumption of repeated use for about 2 to 3 weeks. They do not promise an effect after a single bath, and there are individual differences depending on constitution and condition.

Are hot spring effects determined by the minerals?

Minerals, or chemical effects, are only one factor. Thermal warmth that raises the body’s temperature, physical effects such as hydrostatic pressure and buoyancy in water, and the restorative effect of staying in a hot spring area also play major roles. It is more accurate not to explain health benefits by minerals alone.

Why do I feel better on a hot spring trip?

It is thought to be because not only the bathing effects, but also the travel effects of stepping away from daily life, walking, and sleeping more easily are layered together with lifestyle changes. That is why many people find a relaxed stay more comfortable than a rushed day trip, even at the same hot spring.

Conclusion

Hot spring health benefits are best understood scientifically as the combined result of multiple effects: physical effects such as thermal warmth, hydrostatic pressure, and buoyancy, chemical effects from dissolved minerals, and the travel effect of staying in a hot spring area. These can reasonably explain why stiffness and coldness may ease, the mind may calm down, sleep may come more easily, and fatigue may feel lighter.

At the same time, the Ministry of the Environment’s therapeutic spring and indication framework assumes repeated use over a certain period, does not guarantee effectiveness, and involves large individual differences. The evidence often comes from observational studies and small trials, so it is important not to confuse correlation with causation. Hot springs do not cure disease; they are most realistically used within a manageable range as a way to support rest and condition management.

Sources

• Ministry of the Environment: Definition of Hot Springs (Protection and Use of Hot Springs)
• Ministry of the Environment: Mineral Spring Analysis Guidelines (Revised in 2014)
• Toho Laboratory of Microbial Diseases: “On the June 2014 Ministry of the Environment Notice 'Contraindications and Precautions for Bathing or Drinking'” (Medical Commentary)
• Japan Cosmetic Industry Association: “How to Use Hot Springs and Bathing for Health” (Hideji Matsumoto)