Update Radon is a colorless, odorless gas that is a decay product of uranium and occurs naturally in soil and rock. Radon gas has been identified as a leading cause of lung cancer, second only to cigarette smoking, and it is responsible for thousands of deaths annually. These emissions raise the risk of lung cancer.
Radon enters a home through cracks in walls, basement floors, foundations and other openings.
It may also contaminate the water supply, especially in private wells. Over a person's lifetime, particulate radon progeny can enter the lungs, attach themselves, and may eventually lead to lung cancer. Radon is believed to cause between 15,000 and 21,000 U.S. deaths from lung cancer annually. Radon has been identified in every state. Smokers exposed to radon substantially increase their risk of lung cancer in comparison to exposed non-smokers.