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Radon - Topic Overview

What is radon?

Radon is a radioactive gas that causes cancer. Radon is found in rock, soil, water, some building materials, and natural gas. You can't see, taste, or smell it.

How does radon exposure occur?

Any home, school, office, or other building can have high levels of radon. Radon is found in new and old buildings. It can seep in through the foundation of a house built on radon-contaminated soil. If a house's water supply contains radon, radon may enter the air inside the house through pipes, drains, faucets, or appliances that use water. Then the radon may get trapped inside the house.

Radon sinks to the low points in buildings, so it often is found in basements. But a building can have high levels of radon even if it doesn't have a basement.

Studies show that nearly 1 out of every 15 homes in the United States has unsafe levels of radon.1 If you live in an area that has large deposits of uranium, you may be more likely to be exposed to high levels of radon. (To see a map of the U.S. radon zones, see the website www.epa.gov/radon/zonemap.html.) But the construction features and exact location of your house may be just as likely to affect your risk. Even houses right next to each other can have very different radon levels.

What are the health effects of radon exposure?

Over time, exposure to radon can cause lung cancer. Radon causes about 21,000 lung cancer deaths each year in the U.S. It is the second leading cause of lung cancer, after tobacco smoking.1 People who smoke have an even higher risk of lung cancer from radon exposure than people who don't smoke.

Radon exposure doesn't cause symptoms. Unless your home or office is tested for high radon levels, you may not realize that you are being exposed to dangerous levels of radon until you or someone in your family is diagnosed with lung cancer.

How can you test your home's radon levels?

The U.S. Surgeon General and the U.S. Environmental Protection Agency (EPA) recommend that all homes be tested for radon levels.

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