The first case of radiation induced cancer was reported seven years later. Early human evidence of the harmful effects of ionizing radiation, as a result of high exposures, became available in the 1920s and 30s through the experience of radiologists, miners exposed to airborne activity, and workers in the radium industry. However, the long term biological significance of smaller, repeated doses of radiation was not widely appreciated until later. Genetic effects which occur in the reproductive cells and may be inherited. Somatic effects which arise from damage to all cells in the body and are observable in the individual affected.
Genetic effects are essentially long term in nature since they are manifested in offspring.
The terms acute and chronic are also used to describe the period during which the radiation exposure is carried out. Somatic effects may also be categorized as non-stochastic or stochastic. In some irradiations, the biological response increases in severity as the dose increases. Such a response is termed non-stochastic and usually exhibits a threshold dose below which the response is not observed. Other irradiations produce a response such as leukemia where the severity is independent of dose, the disease is either contracted or it is not.