From the CDC: "Radon comes from the breakdown of elements like uranium and radium in soils and rocks like granite. Radon is odorless, tasteless and colorless and can only be detected through testing."
The problem is when radon gas from underneath the home leaks in through cracks or gaps. When you breathe in radon gas, the radioactive particles can get trapped in your lungs. Over time, they can cause lung cancer. The risks from radon depend on two things. HOW MUCH & HOW LONG.
In the United Sates, Radon is the #2 cause of lung cancer after smoking and it is estimated to cause over 20,000 deaths each year.