The most lethal damage that radon can cause to any human being is lung cancer. It is the second most important cause of lung cancer after smoking. Radon may seep out from the ground in open spaces but because the air gets diluted, the risk to individuals is not high.
This threat is increased manifold when the air is confined to closed spaces, like the inside of your homes, because radon may build up to an alarming level and cause higher risks. The risk of lung cancer from radon inhalation is an active threat for both smokers and non-smokers.