What is Radon? Radon is a natural gas that’s produced when uranium in the soil breaks down, and it’s released into the air and water. Unfortunately, radon is completely undetectable by humans, so you could be exposed to high levels of radon and not even know it! Radon is the second leading cause of lung cancer (after cigarette smoke), and the EPA estimates that radon leads to more deaths each year than drunk driving. If you smoke or live with someone who does, your risk of de