Final answer:
Radon, a radioactive gas, can seep into homes from the ground below and is potentially cancer-causing. It comes from the natural decay of uranium or thorium found in soil and can enter through cracks in floors, walls, and foundations. Long-term exposure to radon can increase the risk of lung cancer.
Step-by-step explanation:
Radon is a radioactive gas that is naturally-occurring, colorless, and odorless. It comes from the natural decay of uranium or thorium found in nearly all soils. It typically moves up through the ground and into the home through cracks in floors, walls and foundations. It can also be released from building materials or from well water. Radon breaks down quickly, giving off radioactive particles. Long-term exposure to these particles can lead to lung cancer. Radon is the leading cause of lung cancer among nonsmokers, according to the U.S. Environmental Protection Agency, and the second leading cause behind smoking.