Radon is a radioactive, colourless and odourless gas that is found all around us in very small amounts and is responsible for most of our daily dose of radiation. Radon gas is one of the decay products of radium, which in turn is a decay product of uranium – the most common naturally occurring radioactive substance on Earth. Small amounts of uranium are found in the soil, with an average 2.6 square kilometres (one square mile) of surface soil containing about one gram (0.03 ounces) of radium. Radon gas seeps into the atmosphere from the ground, where its primary way of entering the body is by inhalation. This doesn’t pose a serious health risk, though, as levels are generally low. However, some places have higher concentrations of uranium, leading to dangerous buildups of radon gas, particularly inside homes where the gas can’t easily escape. Radon gas is the second-biggest contributing factor toward lung cancer after smoking, as it continues to decay inside the lungs, damaging living tissue.
Answered by Rik Sargent