Radon is a cancer causing, radioactive gas. You cannot see it, smell it or taste it. Radon is produced by the natural breakdown of uranium in soil, rock and water. High levels of radon have been found in every state in the US. One in fifteen homes in the US have radon levels above 4 picocuries per liter (4pCi/L), the EPA action level.
Radon is the second leading cause of lung cancer in the United States. Of the 160,000 lung cancer deaths annually in the United States, about 12% are due to radon exposure. The remainder is due to smoking. According to the National Academy of Sciences, radon is estimated to cause about 21,000 deaths per year.