Indoors, however, radon can accumulate in your home and build up to dangerous levels. High levels of radon in your home can increase your risk of developing lung cancer. When radon gas naturally breaks down, it forms radioactive decay products. When you breathe air that contains high levels of radon, these radon decay products can become trapped in your lungs. As they further break down, the decay products release small amounts of energy which can damage lung tissue and lead to lung cancer.
Radon is second to smoking as the major cause of lung cancer deaths.
At higher levels in your home, the effect of radon on your body and the risk of developing lung cancer has been compared to that of a heavy smoker. The amount of radon in your home will depend on your home's construction and the concentration of radon in the soil under your home. Because radon is a gas, it can move through small spaces in the soil and rock on which a home is built. Radon can enter a home through dirt floors, cracks in concrete floors and walls, floor drains, sumps, joints where the wall and floor meet, and tiny cracks or pores in hollow-block walls. Radon can also enter water in private wells and is freed when the water is used.