Radon in homes is the second leading cause of lung cancer. Radon is the No. 1 cause of lung cancer among non-smokers. The passage of a single alpha particle can cause mutations of DNA, and some cells may become cancerous.
Most cancers originate from damage to a single cell.
The more radiation particles pass through the human body, the higher the chances of developing cancer. Therefore, the risk to people is proportional to the length of exposure and the radon concentration in air. But at lower concentrations, like at home, every emitted particle counts. Radioactivity is dangerous at any level and even the low levels of radon gas outdoors are not harmless. The higher the radon level in one's home, the higher the radioactive dose to the family.