Radon is a colorless, odorless gas produced naturally outdoors in harmless amounts from the breakdown of uranium in soil and rocks. Sometimes, it can get concentrated in homes built on soil with natural uranium deposits, or it can enter buildings through cracks in floors or walls, construction joints, or gaps in foundations around pipes, wires, or pumps. Radon levels are usually highest in the basement and / or crawl space.
You cannot see, smell or taste radon. But it still may be a problem in your home. When you breathe air containing radon, you increase your risk of getting 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. If you smoke and your home has high radon levels, your risk of lung cancer is especially high.