Damage to cells and intracellular molecules by x-rays, gamma rays, radionuclides, or other sources of radioactive energy. In sufficient doses, radioactive energy can damage the cytoplasm and the genetic material of the cell, leading to organ dysfunction (especially in rapidly dividing tissues such as the skin and the lining of the gastrointestinal tract), mutations, inhibition of cell division, cell death, or carcinogenesis. When the developing fetus is exposed to radiation in the womb, developmental malformations may result.