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 are not. These particles are inhaled and become lodged in the lungs. Once lodged, they can radiate and penetrate lung tissue, initiating the process of carcinogenesis. For smokers, the news is even worse.
Smoking increases the risk of exposure to radon.
When tobacco crops are fertilized, radon gas collects under the thick canopy of tobacco leaves, and tiny dust particles impregnated with radon daughters cling to the sticky, resinous hairs on the underside of each leaf. With every inhalation, cigarette smokers breathe these radon daughters into their lungs. These tailings contain 85 percent of the original radioactivity. As a result, some homes contain levels of radon gas and radon daughters even higher than those permitted in the mines. Health Canada warns that factors such as the location of a house and its relation to the prevailing wind may be just as important as the source of the radon.