Radon is a naturally occurring radioactive gas that results from the decay of uranium in rocks and soils. The gas is colourless, odourless and tasteless and can only be measured using special equipment.
In the open air, radon is harmless. But in an enclosed space such as a house, it may build up to an unacceptably high level. Radon from the ground enters buildings chiefly through cracks in floors or gaps around pipes or cables.
How is it harmful?
Radon decays to form tiny radioactive particles, some of which stay suspended in the air. When you inhale these particles, they give a radiation dose that may damage your lungs.
Radon has been shown to be a cause of cancer, specifically lung cancer. Remaining exposed to high levels of radon in an enclosed area can increase your risk of lung cancer, particularly if you smoke.