But it is found in many homes and buildings.
Radon is the second leading cause of lung cancer in the United States today.
Scientists are more certain about radon risks than risks from most other cancer-causing substances. Radon gas comes from the natural radioactive decay of uranium that is found in nearly all soils and rocks. It typically moves up through the ground to the air above and into homes through cracks and other holes in the foundation. Radon can become trapped inside the home and accumulate. Any home may have a radon problem.