Radon is a colorless, tasteless, and odorless noble gas that occurs naturally when the element radium breaks down in the environment. It is radioactive and has a half-life of 3.8 days. It is at its most stable when it is an isotope. It is easily inhaled, causing it to be one of the primary contributors to the onset and formation of lung disease. The Environmental Protection Agency (EPA) estimates that about 21,000 people die each year from lung cancer related to radon gas exposure, making radon the second leading cause of lung cancer death in the US.