The Biological Effects of Radiation Whether the source of radiation is natural or man made, whether it is a small dose of radiation or a large dose, there will be some biological effects. Radiation causes ionizations of atoms, which will affect molecules, which may affect cells, which may affect tissues, and so on. Although most people tend to think of biological effects in terms of the effect of radiation on living cells, in actuality, ionizing radiation, by definition, interacts only with atoms by a process called ionization (Chandra p. 205). Thus, all biological damage effects begin with the consequence of radiation interact