Some of the short-lived radon daughters attach themselves to small particles in the air, which can be inhaled deep into the lungs. The radon daughters may then damage dividing lung cells, possibly resulting in lung cancer. Radon gas is thought to be responsible for 5,000 to 20,000 lung cancer deaths per year in the United States. Indoors, however, radon can become more concentrated because of the lack of ventilation in homes combined with exhaust fans that draw air. Radon gas can seep into a house through dirt floors, cracks in concrete floors and walls, floor drains, sump pumps, and joints.
Radon gas can also accumulate in private wells and be released into the home when water is used.
This is normally not a problem for large community water supplies. The level of radon that can build up indoors depends upon the amount of radon in the source material and the rate at which it is removed from the home by ventilation. Homes tested throughout the U.S. show a wide range of radon concentrations. Spend less time in areas with higher concentrations of radon, such as the basement. Whenever practical, increase the airflow into and through your house, especially in the basement.