This page was reviewed under our medical and editorial policy by
Maurie Markman, MD, President, Medicine & Science
This page was updated on June 13, 2022.
In many parts of the United States and around the world, a colorless, odorless gas called radon naturally emanates from rock, soil and water underneath homes, schools and places of work. It’s always in the air, and you’re likely breathing it in at low levels all the time. In the long term, frequent exposure to high levels of radon may increase the risk of lung cancer. However, you may take certain measures to identify radon in your environment and, if detected, to limit your exposure.
Radon is a radioactive gas released into the air when certain radioactive elements, such as uranium, thorium and radium, break down. Radon is found both indoors and outdoors. The highest concentrations of radon are typically in underground, unventilated spaces such as mines. Radon may easily seep into homes through cracks in the foundation and walls. It may also be present in rivers, lakes, streams, wells and other water sources. You can’t see or smell radon, but simple detection kits may help determine the levels of radon present in air and water.
People who work in mines or facilities that process uranium, or who come into contact with phosphate fertilizers, are among those facing the most exposure to high concentrations of radon.
The general public may be exposed to radon inside of any building that’s located on soil from which radon naturally emanates, whether it’s your home, workplace or school.
Radon enters through cracks in a structure’s foundation and walls. The basement and ground-level floor of buildings and homes tend to have higher concentrations of radon than other floors. Low levels of radon emitted from building materials, granite countertops and well water may also contribute to exposure.
Elevated levels of radon may be detected in about one in 15 homes in the United States, according to the Environmental Protection Agency (EPA). The EPA publishes a county-by-county map showing regions where high concentrations of radon are most likely.
Long-term exposure to radon, especially at higher concentrations, may increase the risk of lung cancer. Radon emits tiny radioactive particles as it decays. When you breathe air with high concentrations of radon, these particles damage the cells in the lining of your lungs, making them more vulnerable to cancer.
It’s estimated that radon is the second-most common cause of lung cancer in the United States after smoking. It’s important to take steps to reduce radon levels in your environment and, in turn, your cancer risk. Lung cancer is the only type of cancer linked to radon.
In addition to reducing your exposure to radon at home, quitting smoking is another important step to reduce the risk of lung cancer. Radon exposure is more likely to cause lung cancer in people who also smoke cigarettes. Research shows that a combination of high radon exposure with smoking is statistically more dangerous than the lung cancer risk posed from either smoking or radon exposure alone.
State and local environmental agencies provide radon testing assistance and, if concerning radon levels are detected, recommend next steps. In some cases, it may mean hiring a qualified contractor who specializes in radon mitigation. Possible radon mitigation methods range from simply sealing cracks in walls or floors to installing specialized systems that filter radon from well water before it reaches the tap and from the air in your home.
The EPA recommends that all people buying (or selling) a home have it tested for radon and ask whether it was built with radon-resistant construction. It’s possible to measure the levels of radon in a home, either with a do-it-yourself kit or via professional testing. Sometimes testing needs to take place over the course of several days or even weeks to get a proper reading.
If you’re living in a home with high indoor levels of radon, mitigation systems may help reduce radon in the air and/or water. The EPA advises that you take steps to reduce radon if testing finds that your radon levels reach 4 picocuries per liter (pCi/L) or higher. Even lower levels may pose a risk.
Find local radon resources through the EPA as well as state environmental agencies. If you’re concerned that you may have been exposed to high concentrations of radon, ask your doctor about lung cancer screening. Some employees diagnosed with lung and other cancers as a result of their work in or around uranium mines may be eligible for financial compensation through a federal program called the Radiation Exposure Compensation Act.