In risk management, the biological effects of radiation are differentiated by their mode of appearance: there are deterministic effects, which have an occurrence threshold, and stochastic effects, which appear at random in an exposed population.

Doses of more than 1 sievert delivered in just a few hours induce in every exposed person effects whose severity increases with the dose.

Our present knowledge of the effect of low doses only allows us to make statistical predictions: if every person in a population of 100 people has received a total dose of 1 Sv during his lifetime, it is estimated that the number of people with cancer will rise from 25 to 30 although the 5 additional, radiation-induced cases will be indistinguishable from the others.