When alpha particles hit something, the energy in them is absorbed on the surface of whatever they hit. Human skin is thick enough not to be affected, but bronchial and lung tissue is not. Alpha particles in the lungs can damage lung tissue and lead to lung cancer. Studies of the incidence of lung cancer among uranium miners conducted in Canada during the 1970s showed a correlation between radon exposure and deaths from lung cancer. While we can and do assume a correlation between lung cancer and radon in homes, such a link has not been demonstrated perhaps because many people smoke tobacco which also causes lung cancer.
Radon gas can move through small spaces in the soil and rock on which a house is built.
It can seep into a home through dirt floors, cracks in concrete walls and floors, sumps, joints, basement drains, under the furnace base, and jack posts if the base is buried in the floor. Concrete-block walls are particularly porous to radon. Radon trapped in water from wells can be released into the air when the water is used. A survey conducted in the late 1970s by Health Canada showed that radon levels in certain Canadian cities were higher than in others. However, measurements have been made in thousands of houses in Canada, and so far it has not been possible to predict whether any one house will have a high radon level or not.