Radon is a radioactive gas emitted naturally from the ground. You cannot see, smell, or taste radon. But it still may be a problem in your home. However, when radon gets trapped indoors—after entering a home through joints in walls, basement floors, foundations and other openings—it may concentrate at dangerous levels. And exposure to high levels of radon can cause lung cancer. In fact, the Surgeon General of the United States has warned that radon is the second leading cause of lung cancer in the United States today.