Answer:
On the body? High energy radiation, such as the EM waves beyond and including UV, i.e. X-ray, gamma. Have the adverse effect of damaging human DNA, which over time causes mutations, resulting in cancer or organ failure. Short exposure to large doses of radiation damages the tissue that has been exposed to it, the risk of mutation is lower due to the short exposure time, but tissue may be severely damaged by the radiation leading to internal bleeding. There could also be severe and permanent scars to where the radiation was close to. Also, it could lead to death of course.