Hormesis: are low doses of ionizing radiation harmful or beneficial?

A review is provided of the literature on radiation hormesis, hormesis being any physiological effect that occurs at low doses and which cannot be anticipated by extrapolating from toxic effects noted at high doses. Epidemiological studies suggesting beneficial effects are considered, and experimental evidence for the existence of hormesis is then appraised. In the latter context, there are possible low-dose effects at the molecular level, at the cellular level and on the organism as a whole. It is concluded that while it is difficult to analyse the effects of low-dose radiation with statistical significance, the concept does permit the reconsideration of the validity of currently accepted notions.