Background radiation mainly comes from natural sources, which include cosmic rays, soil and rocks and living things, according to the BBC. Artificial radiation originates mainly from types of medical examinations like X-ray photographs.
The radiation that comes from cosmic rays is a type of radiation from space that reaches Earth. Certain types of soil and rocks are radioactive, and they give off radioactive radon. Living things become radioactive when they absorb a radioactive material from sources like soil. These radioactive materials are then passed along the food chain. Radiation in humans can cause damage to cells, which can cause these cells to become cancerous.