Radon is a colorless, odorless radioactive gas that forms when naturally occurring uranium decays. Radon gas is commonly found in rocks and soil, and it enters homes through cracks and other holes in the foundation. Prolonged exposure to radon levels above 4 picocuries per liter of air significantly increases the risk of lung cancer, even for nonsmokers. The USEPA considers radon the second leading cause of lung cancer in the United States overall, and it is the leading cause among non-smokers. The only way to find out if you have elevated radon levels in your home is to conduct a simple test.