Radon is produced as a result of the radioactive decay of uranium-238, a naturally-occurring radionuclide found within rocks and soils. Approximately 99% of all uranium is in the form of uranium-238, which decays through a long chain of radionuclides that includes radon-222. Being a gas, radon can move through porous materials, or escape through cracks, and can find its way into our homes. Most of our background exposure to ionising radiation is due to breathing radon-222 and its decay products (sometimes called ‘radon daughters’). The radionuclides can be inhaled directly from the air, or may become attached to particles of household dust, which are subsequently inhaled. The radionuclides may then be deposited in the lungs. Some will remain in the body, some will be removed. There’s a chance that they may decay (and emit ionising radiation) before your body can get rid of them, resulting in a radiation dose.