National Cancer Institute.
Radon is a radioactive gas released from the normal decay of the elements uranium, thorium, and radium in rocks and soil.
Radioactive particles from radon can damage cells that line the lungs and lead to lung cancer.
Radon is the second leading cause of lung cancer in the United States and is associated with 15,000 to 22,000 lung cancer deaths each year.
Testing is the only way to know if your home has elevated radon levels. Health authorities recommend radon testing and encourage corrective action when necessary.