Hot Springs Are Not Omnipotent? What You Need to Know About the "Hidden Side"

Hot springs are a familiar place of healing for Japanese people, but not all of them contain only "good ingredients." While efficacy claims have been passed down for centuries, hot spring water can contain trace metals derived from soil and geological strata, and sometimes harmful minerals such as arsenic, cadmium, lead, and aluminum are detected. We have also visited and investigated several hot spring areas, and we were reminded of the importance of checking the spring quality analysis report, rather than being solely captivated by the efficacy claims.

Typical Harmful Minerals Found in Hot Springs

Arsenic (Arsenic)

Arsenic is divided into inorganic and organic arsenic, with inorganic arsenic (trivalent and pentavalent arsenic) being particularly toxic and problematic. There have been reports of high concentrations of total arsenic detected in some hot springs in Japan, with some cases showing a high proportion of trivalent arsenic. While the effects of drinking the water are the main focus of discussion, some research and cases suggest accumulation in the skin, nails, and hair.

Heavy Metals such as Cadmium, Lead, and Mercury

Cadmium, lead, and in some cases, trace amounts of mercury may be present. These primarily pose problems with chronic exposure, raising concerns about effects on kidney and neurological function. Since the composition varies greatly from one hot spring to another, it cannot be uniformly labeled as "dangerous," but the risk of long-term accumulation cannot be ignored.

How Much Should We Worry About Transdermal Absorption?

It's easy to think, "It's fine as long as I don't drink it," but absorption through the skin and mucous membranes cannot be completely ignored. While the skin has a barrier function, absorption is more likely to occur when there are wounds or inflammation, or near mucous membranes (eyes, nose, mouth). Research and analysis reports suggest that inorganic arsenic in hot springs can be absorbed through the skin and remain in body tissues. The risk of acute poisoning is rare, but repeated exposure to high concentrations raises concerns about chronic effects, so pregnant women, small children, and those with impaired kidney function need to be especially careful.

Also Beware of Chlorine and Chloramine in Public Baths and Pools

Chlorine-based disinfectants are used in public baths and pools for disinfection. This is necessary for killing Legionella and E. coli, but chloramine, formed by the reaction of chlorine with ammonia in sweat and urine, is the cause of the pungent odor. Chloramine can cause respiratory irritation, eye redness, and skin problems, and special caution is needed for those with respiratory illnesses such as asthma. We also use hot springs and public baths, and we try to limit our time in facilities with this strong, distinctive odor.

Practical Measures to Reduce Risk

Check Spring Quality Displays and Analysis Reports

Check the spring quality display and ingredient list of the hot spring you want to visit. Many hot spring facilities display ingredient analysis reports, and if you have any questions, the staff are often kind enough to explain them directly.

Be Mindful of Skin Condition and Stay Duration

If you have wounds or dermatitis, refrain from bathing. Avoid long baths. We recommend that children, pregnant women, and people with chronic illnesses consult a doctor beforehand. A quick shower after bathing can reduce residue on the skin surface.

Tips for Using Public Baths and Pools

In facilities with a strong chloramine odor, it is effective to use them during well-ventilated hours, cover your eyes and nose with a towel to avoid irritation, and rinse thoroughly with water after use.

Summary

Hot springs are a wonderful culture that heals the mind and body, but the spring quality varies greatly depending on the location, and trace amounts of harmful minerals and disinfection byproducts may be included. Acute danger is rare, but absorption through the skin and mucous membranes and accumulation due to long-term exposure cannot be completely denied. We, the geefee team, also recommend enjoying hot springs after understanding not only their benefits but also their risks. Please check the spring quality before bathing and try to use it in a way that suits your physical condition and skin.

Disclaimer: The information in this article is for general informational purposes only and does not constitute medical advice. Please consult a qualified healthcare professional before making any health-related decisions.