Damaged DNA gets repaired. The proposed mechanism for hormesis is that low levels of radiation stimulate the repair process and get the immune system to step in earlier. I have no idea if this is really true, but it doesn't seem absurd on its face.
There's no observed instance of such "earlier repair," it's just an invented "hypothesis." Only the non-linearity is observed, and not even by majority of the experiments. The explanation for the observed non-linearity is that the single impacted cells simply have time to die (or be targeted by the white cells) at low levels, whereas at higher dosages there are enough cells for cancer to progress more often. It's just the game of probabilities at the levels at which we have enough noise (low enough doses).
