Radon is a radioactive gas that forms when radioactive metals like uranium, radium, or thorium break down in the soil, rocks, and groundwater. Radon is present everywhere in the earth. This colorless, odorless gas rises up through the soil and rocks and enters your home through tiny cracks and gaps in the foundation.
Because radon is everywhere, you are constantly exposed to low levels of it, and it is typically not harmful at those low levels. However, when radon is trapped in your home and becomes concentrated enough, it becomes a serious health risk. Exposure to elevated levels of radon is the second leading cause of lung cancer.