Every biological organism on earth is exposed to both ionizing and non-ionizing radiation and to their effects. The main sources of radiation are present in nature (sun, earth), but radiation can also be produced artificially. Ionizing radiation causes brakes in the chemical bonds of molecules in the cell and also in chromosomes, resulting in DNA strand brakes called mutations. These mutations may result in cell death or, in the long term, transformation into a cancer cell. However, as a cause of cancer, ionizing radiation comes after smoking and bad nutritional habits. An important reduction in cancer incidence can be achieved by elimination of smoking, improved nutritional habits, and avoidance of cancerogens and excessive exposure to sunlight.