@ GlassAxe- Ionizing radiation has a negative effect on DNA (radiation from x-rays, etc.). The Clinton Administration established a committee to study the effects of ionizing radiation on humans. The Advisory Committee on Human Radiation Experiments, studied human effects from many events including the aftermath of Hiroshima and the human effects of researchers of the Manhattan Project.
In their research, they concluded that ionizing radiation has the ability to break the chemical bonds of molecules in our body. Radiation affects DNA molecules in two ways. In a direct action, a radioactive isotope ejects an electron that directly affects the DNA molecule, potentially causing genetic mutations. In an indirect action, the free electron strikes a water molecule, causing it to become a free radical (an unstable molecule). This free radical drifts around looking for another molecule to react with, potentially a DNA molecule.
Long-term exposure to somatic cells will result in cancer, while long-term exposure to germ cells (egg and sperm) can lead to genetic mutations.