low as 100 to 199 Bq m−3 and warned that smoking greatly increases the risk posed by radon exposure i.e. reducing the prevalence of smoking would decrease deaths caused by radon. However, the discussion about the opposite experimental results is still going on, especially the popular US and German studies have found some hormetic effects. Furthermore, particle microbeam studies show that passage of even a single alpha particle (e.g. from radon and its progeny) through cell nuclei is highly mutagenic, and that alpha radiation may have a higher mutagenic effect at low doses (even if a small fraction of cells are hit by alpha particles) than predicted by linear no-threshold model, a phenomenon attributed to bystander effect. However, there is currently insufficient evidence at hand to suggest that the bystander effect promotes carcinogenesis in humans at low doses. Statements by leading nuclear bodies Radiation hormesis has not been accepted by either the United States National Research Council, or the National Council on Radiation Protection and Measurements (NCRP). In May 2018, the NCRP published the report of an interdisciplinary group of radiation experts who critically reviewed 29 high-quality epidemiologic studies of populations exposed to radiation in the low dose and low dose-rate range, mostly published within the last 10 years. The group of experts concluded: The recent epidemiologic studies support the continued use of the LNT model for radiation protection. This is in accord with judgments by other national and international scientific committees, based on somewhat older data, that no alternative dose-response relationship appears more pragmatic or prudent for radiation protection purposes than the LNT model. In addition, the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) wrote in its 2000 report: Until the [...] uncertainties on low-dose response are resolved, the Committee believes that an increase in the risk of tumour induction proportionate to the radiation dose is consistent with developing knowledge and that it remains, accordingly, the most scientifically defensible approximation of low-dose response. However, a strictly linear dose response should not be expected in all circumstances. This is a reference to the fact that very low doses of radiation have only marginal impacts on individual health outcomes. It is therefore difficult to detect the 'signal' of decreased or increased morbidity and mortality due to low-level radiation exposure in the 'noise' of other effects. The notion of radiation hormesis has been rejected by the National Research