How radiation affects a person depends on the type of radiation, how much is absorbed by the body, the length of time a person is exposed, and the route of exposure.

When a person is exposed to radiation, it harms their cells first. Radiation moves very fast and because of this it has enough power and energy to knock electrons away from the atoms. These atoms make up the molecules, and when molecules lose their electrons, they are called ions. Cells are made of molecules, and when the molecules become ions, they disrupt the way the cell functions. When radiation harms a cell in the body, it can also harm the DNA because its at the heart of a cell.

The body can take three different routes when exposed to radiation: 1) the injured cells repair themselves, 2) the cells die, as do millions of other cells in the body, and are immediately replaced, 3) the cells incorrectly repair themselves, causing a biophysical change. High dosages of radiation tend to kill cells, while lower ones tend to injure them, causing them to repair themselves, sometimes incorrectly. When cells are killed quickly, the tissues and organs are immediately affected.