Radon

Source: MedlinePlus Health Topics, U.S. National Library of Medicine

Last synced 8/6/2026Status: primary verified

What is radon? Radon is a naturally occurring radioactive gas. It is invisible and has no odor or taste. It comes from the normal decay of uranium and thorium. These are two chemical elements that can be found in soil, rock, and groundwater. Radon breaks down quickly, giving off radioactive particles. Over time, breathing in high levels of these particles can cause lung cancer . How would I be exposed to radon? Outdoors, there are low levels of radon in the air. But radon can also be indoors. It can enter homes and buildings through cracks in the floors, walls, or foundations. Certain building materials can give off radon. And sometimes radon gets inside through well water. Radon levels can be higher in homes and buildings that are well insulated, tightly sealed, and/or built on soil that has a lot of uranium and thorium. Basements and first floors usually have the highest radon levels because they are closer to the ground. How does radon cause lung cancer? When you breathe in radon, its radioactive decay products can get trapped in your lungs. They can damage the cells that line your lungs. Over time, it can lead to lung cancer. It may take years before this happens. Radon is the second leading cause of lung cancer deaths after cigarette smoking . If you smoke and are exposed to radon, your risk of lung cancer is much higher than if you did not smoke. Most radon-related cancer deaths happen in smokers. How do I know if my home has high levels of radon? Testing is the only way to know if there are high levels of radon in your home. You should test your home's radon levels: If it's never been tested or the radon levels are unknown When preparing to buy or sell your house Before and after any renovations, especially after making any repairs to reduce radon levels Before making any lifestyle changes in the home that would cause someone to spend more time in the basement or lower level (such as converting a basement to a bedroom) Testing is fairly inexpensive and easy t

Educational only

This information is for general education and is not medical advice. Always talk to a licensed U.S. clinician about your situation, medications, or treatment decisions.