The radon therapy differs significantly from normal speleotherapy. Here, the noble gas radon is used, which occurs in all rocks, but is heightened in certain rocks. In mines, especially those in volcanic rocks, the gas therefore accumulates. Again, the patient spends many hours in the therapeutic gallery as part of a therapy, which consists of breathing in the radon-rich air. It helps especially with chronic diseases of the respiratory tract, the musculoskeletal system and the skin.

However, unlike the other variants, this therapy cannot be called harmless. The harmful effects of radon on health, especially the increased risk of cancer, were recognized several decades ago. These days, underground workplaces must be regularly tested for radon, and this applies not only to mines, but also to show caves and other tourist objects. If the radon content is too high, certain times must not be exceeded. Radon is a noble or inert gas and does not react with the body, is not metabolized and is therefore completely non-toxic. However, natural radon has a certain amount of a radioactive isotope and is therefore radioactive. In this respect, a therapy in a radon tunnel is more or less harmless, but working there increases the exposure to natural radiation and must be checked.

Taking the Gastein Heilstollen as an example, it looks like this: The effective radioactive dose of a 3-week therapy with 10 applications in the Gastein gallery is about 1.8 mSv. If they are not exposed to radiation either occupationally or medically, the EU states define an additional exposure of 1 mSv per year as the upper limit. This is therefore clearly exceeded by the three-week therapy. As a result the radon tunnel is a control or monitoring area according to the Radiation Protection Ordinance. On the other hand, the exposure is significantly higher for people who live in the mountains, in areas with radioactive ores such as the Black Forest or the Ore Mountains, or who work in aircrafts like pilots or flight attendants.

However, the bigger problem with radon therapy, as with all variants of speleotherapy, is that there is no scientifically based recommendation for radon therapy. There are a large number of publications suggesting effectiveness, but none that satisfies the scientific requirements for proof of effectiveness. However, the therapies are recognized as treatment by the Austrian social insurances for Bekhterev's disease, rheumatoid arthritis and psoriatic arthritis. Many health insurances pay for such therapies at least partly.