Radon is a colorless, odorless radioactive gas. It comes from the natural decay of uranium or thorium found in nearly all soils. It typically moves up through the ground and into the home through cracks in floors, walls and foundations. It can also be released from building materials or from well water. Radon breaks down quickly, giving off radioactive particles. Long-term exposure to these particles can lead to lung cancer.
The U.S. Environmental Protection Agency estimates that radon causes about 21,000 lung cancer deaths in the United States each year. While other estimates might be higher or lower, there is general agreement that radon exposure is the second leading cause of lung cancer after active smoking and the leading cause among non-smokers. Many radon-related lung cancer deaths can be prevented by testing for radon and taking the necessary steps to lower radon exposure in homes that have elevated radon levels. This process is known as radon mitigation.