Radon is a radioactive gas that is released by the normal decay of three elements: radium, thorium and uranium. These elements naturally exist in rocks and soil, making radon gas widespread. When these elements decay, the radon gas seeps up from the ground and escapes through soil into the air above.
It is also possible – depending on the area – for radon gas to dissolve into ground water. It then transfers to the air after the water is used. The gas itself is invisible, odorless and tasteless.
While radon gas exists almost anywhere, it is usually only present at very minor levels in outdoor areas. Areas with closed ventilation like mines can see much higher levels of radon. If someone inhales air in these kinds of places for a prolonged period of time, it can lead to serious problems like lung cancer.