These scanners work in two ways. One type uses nonionizing electromagnetic radiation (millimeter waves), a form of energy similar to that used in radar images and radio signals. This type of radiation, which has been used for a century, has no known health effects. The other type of scanner uses "back scatter" ionizing radiation, which exposes an individual to a very weak X-ray signal. The radiation emitted from the scanner is weak enough that the X-ray doesn't penetrate the body.