Radon is a natural radioactive gas that occurs in the Earth’s crust. Radon is part of a long radioactive decay chain that starts with uranium that has been present in rocks and soil since the Earth was formed. Radon cannot be sensed by humans as it has no colour or smell, but it can be measured because of its radioactivity. Radon gas is drawn into homes from the ground. Some homes have high concentrations of radon, especially those in areas with more natural uranium in the soil and rocks. Radon can also be present in building materials and drinking-water, but in most cases, these cause much less radiation exposure than radon from the ground.

Whereas radon itself is a gas, its radioactive decay products are not, and they stick to dust particles in the air. As we breathe in the decay products, the radiation they emit can damage our lungs.

Exposure to radon increases our risk of lung cancer. The extra risk is proportional to the radon concentration in the air we breathe and to the duration of radon exposure.