There is no safe radiation threshold.

The health effects associated with exposure to low doses of radioactivity remain controversial. The effects of low doses, if any, are so small that they have not yet been confirmed. By adopting the "linear no-threshold” dose-effects model, radiation protection organizations are making a deliberately conservative choice to protect populations.

A Controversial Topic 

The health risks associated with exposure to low doses of radioactivity are controversial as there is no scientific consensus regarding the health effects due to exposure to doses below 100 mSv [1].

The effects of low doses, if they exist, are so small that trying to focus on them requires epidemiological studies involving several hundred thousand people [2].

Several possible models

Faced with this situation, researchers on the subject sought to model the effects of exposure to low doses (lower than 100 mSv). Two main approaches are used: the Linear No-Threshold (LNT) model and the Linear Threshold model. It should be noted that there are, however, other models that go beyond the scope of this short explanation [3]. The LNT model states that the effects of ionizing radiation increase proportionally with dose, without the possibility of establishing a harmlessness threshold. Biological effects are therefore extrapolated from effects at higher doses for which health effects have been detected [3]. The linear threshold model postulates the existence of a harmlessness threshold. Below the threshold, irradiation does not produce an effect, and above it, effects progress in a linear fashion [3]. The radiation protection community has not yet come to a clear consensus on this topic. The IRSN, for example, expressed a favorable opinion in 2023 on the use of the linear no-threshold model for radiation protection [4], while some members of the French Academy of Medicine question its use for very low doses (doses below a few mSv) [5]. Pending scientific progress that would resolve the issue, the LNT model remains the most widely used model [3].