Radon is a radioactive gas released from the decay of uranium in rocks and soil. It is an invisible, odorless, and tasteless gas that seeps up through the ground and diffuses into the air. In a few areas, depending on local geology, radon dissolves at high concentrations in ground water where it can then be released into the air when water is used. Out of doors, radon gas exists at harmless levels. However, in areas without adequate ventilation, such as underground mines, radon can accumulate to levels that substantially increase the risk of lung cancer .
Radon quickly decays, emitting tiny radioactive particles.
When inhaled, these radioactive particles can damage the cells lining the lung. Long-term exposure to radon can lead to lung cancer, the only cancer proven to be associated with inhaling radon. Everyone breathes in radon every day, but mostly at very low levels resulting in little adverse effect. However, people who inhale high levels of radon gas may be at an increased risk for developing lung cancer. Radon enters homes through cracks and holes in the foundation, and can even be released from running water though radon from water makes a substantial contribution to total indoor radon levels in only few areas of the country.