Below a minimum threshold dose, the effects of ionizing radiation on the organism are no longer measurable. Two contrary hypotheses (hormesis versus linear dose-response relationship) coexist at the low-dose level. Therefore, on this basis neither affirmation nor rejection or radon-therapy use in health-spas is possible.

The exposure of patients to radon and its short-living daughter nuclei, especially to the lungs, is significantly higher in certain therapeutic applications than the “natural” annual dose of ionizing radiation. Spa personnel may easily exceed the annual limit of 50mSv set for the nuclear industry by the german commission of radiation protection. Nevertheless, at this level of irradiation there is still only a small health risk to the individual. On the other hand, no evidence of positive effects due to alpha-rays have been demonstrated in diseases for which radon-therapy is recommended. The hypothesis of a general “radiation-hormesis” is insufficient to support the proposed beneficial effects of radon-therapy. Most likely the positive results achieved in radon-balneotherapy originate from spa-specific factors (temperature, air humidity etc.), which are independent of the ionizing radiation. Radon-therapy may be considered a relic of the past, when biopositive effects were expected from ionizing radiation.