While most people do not have serious reactions to the contrast dye used in CAT scans, the most common side effects while being injected include hot flashes and a metallic taste in the mouth, according to Imaginis. Some patients also experience itchy hives, which can appear on the body within minutes or even hours after the shot. In rare cases, more serious side effects are reported which require immediate treatment, such as difficulty breathing and swelling of the throat or other areas of the body.
Side effects are more commonly seen with the traditional contrast dye, due to the iodine content. However, newer forms of "non-ionic" contrasts, which contain different chemical structures of iodine, typically cause fewer side effects, as noted by Imaginis.
During a CAT scan, a contrast agent is used to highlight specific organs, blood vessels other tissue, which helps make signs of disease or injury more visible when reading the scan. When injected, the dye is placed directly into a vein, after which it travels through the circulatory system until it is eventually removed from the body by the liver and kidneys. In addition to injections, dyes are also give orally, rectally and, very infrequently, through inhalation.