Radon is a radioactive gas that comes from the soil. Air pressure inside your home is usually lower than pressure in the soil beneath and around your home’s foundation. Because of this difference in air pressure, your house acts like a vacuum, drawing radon in through foundation cracks and other openings. Radon may also be present in well water and can be released into the air in your home when water is used for showering and other household uses. In most cases, radon entering the home through water is a small risk compared with radon entering your home from the soil. Fortunately, radon does not generally present a health risk outdoors because it is diluted in the open air. Radon can, however, build up to dangerous levels inside a house, any other buildings, or caves. As radon gas breaks down, it emits high-energy alpha particles. These particles are in the air we breathe, and once inhaled, they can be deposited in our lungs. The energy associated with these particles can alter cell DNA, thus increasing the risk of lung cancer. Persons who smoke and live in a home with elevated radon levels are at a very high risk to develop lung cancer.
Resource: Healthy Homes Radon – TN Dept of Health https://www.tn.gov/health/cedep/environmental/healthy-homes/hh/radon.html