Radon is a naturally occurring gas that can have a big impact on indoor air quality and your health.

You can't see or smell radon, and it can build up inside homes, buildings and schools to dangerous levels. Exposure to high levels of radon can cause lung cancer. Learn about radon, how it affects lung health and what you can do about it.

Radon is a colorless, tasteless and odorless gas that causes lung cancer. Radon can reside at dangerous levels inside homes, schools and other buildings. Exposure to radon is the second leading cause of lung cancer in the United States, after smoking. Radon-related lung cancers are responsible for an estimated 21,000 deaths annually in the United States.1

Radon forms naturally. Uranium in soil or rock breaks down to form radium, which then turns into radon gas. Once formed, radon enters a home through cracks in walls, basement floors, foundations and other openings. As radon decays, it releases radioactive byproducts that are inhaled and can cause lung cancer. Because radon comes from rock and soil, it can be found anywhere. Exposure to limited concentrations, like those found outdoors, is impossible to avoid. However, when radon gets trapped indoors, it may exist in dangerous concentrations.

Less frequently, radon may enter buildings from water used in bathroom showers and faucets. Concerns have also been raised about the radon released indoors from building materials, such as granite counter tops or tiles. However, these sources have rarely proven to be a problem by themselves.2, 3

Concerns have also recently emerged about radon in natural gas extracted by hydraulic fracturing, or fracking.4 Follow-up research has found that the natural gas coming into homes in the Northeast did not generally contain enough radon to pose a serious additional risk.5

Radon is the second leading cause of lung cancer in the United States, responsible for thousands of deaths each year. Exposure to radon causes no immediate symptoms, but the long-term threat of lung cancer is significant to everyone. People who have never smoked make up approximately 2,900 of the estimated 21,000 radon-related lung cancer deaths each year. 1

The health hazard comes from radioactive particles released when radon decays. These particles can be inhaled into the lung and bombard your cells with dangerous, cancer-causing radiation.4 Smoking and radon exposure can separately increase the risk of lung cancer. But if you smoke, know that exposure to both greatly enhances the risk of lung cancer.

Every home should be tested for radon. Radon has been found at elevated levels in homes in every state and the only way to know is to test. Your home can have elevated levels of radon while your neighbor's home does not. Testing is the only way to determine if you have a problem. Radon testing is easy and inexpensive and it could save your life. Thousands of lung cancer deaths could be avoided each year if home and building owners acted to test and fix.

The only way to detect a buildup of radon in your home is to test the air. Various forms of do-it-yourself test kits and digital detectors are simple to use and inexpensive. See where to get a radon test kit below.

Short-term tests typically take two to seven days. During this time, place the kit in a location where it will not be disturbed, in the lowest level regularly used in your home. Follow the test directions and other official guidance to prevent problems that can affect the testing. Once the testing period is complete, seal the test kit and send it to a laboratory for analysis. Most test kits include the cost of lab analysis and an addressed envelope for submission. In a matter of weeks, you will be notified of the radon level in your home.

Long-term tests tend to be more accurate as they collect more data. They take at least three months and measure long-term averages. If you don't want to wait for a long-term test, short-term tests can indicate if your home has a problem and requires follow-up testing.

Digital detectors can be purchased for your home, and can provide short-term readings and establish an average for the long term.

If you prefer, hire a certified radon-testing professional. The best way to find a certified professional is to contact your state radon program. EPA has an interactive map with contact information for state radon agencies.

Radon gas is measured in picocuries per liter (pCi/L) of air. The EPA recommends taking action to reduce radon if the result is 4.0 pCi/L or greater and to consider similar actions when the radon level is between 2 and 4.0 pCi/L. The ultimate goal is to get your radon level to the lowest level possible.

There are several ways to protect you and your family from the dangers of radon gas.

If you have an existing home with elevated levels of radon, you can fix the problem by having a radon mitigation system installed. A radon mitigation system consists of a vent pipe, fan and the proper sealing of cracks. This system collects radon gas from underneath the foundation and vents it to the outside of your home. If you need to have a radon mitigation system installed, it is best to contact a certified radon mitigation professional to do the installation. A list of certified professionals can usually be obtained by contacting your state radon program.

If you are building a new home, ask your contractor to install radon-resistant features. These features include gravel and plastic sheeting below the foundation, along with proper sealing of cracks and the installation of a vent pipe. Once the radon-resistant features have been installed and the home is completely built, make sure to perform a radon test, as the levels could still be elevated. If the radon levels are still elevated, a radon fan should be added to the system to lower the radon level.

Detailed information about radon reduction in your home or building can be found in EPA's Consumer's Guide to Radon Reduction.

The American Lung Association is working with national partners and government agencies to build in ways to reduce radon in all homes. The National Radon Action Plan outlines strategies to protect millions more people from dangerous radon exposure.

  • National Radon Action Plan

  • Reflections on the National Radon Action Plan's Progress 2015-2020

  • Radon Testing and Home Sales – A Case Study

  1. U.S. Environmental Protection Agency. Radon Health Risks. Accessed August 19, 2016.

  2. U.S. EPA. Indoor Air Quality. What about Radon and Radioactivity in Granite Countertops? Accessed August 19, 2016.

  3. U.S. EPA. Indoor Air Quality. A Citizen's Guide to Radon. Accessed August 19, 2016.

  4. Casey JA, EL Ogburn, SG Rasmussen, JK Irving, J Pollak, PA Locke and BS Schwartz. 2015. Predictors of Indoor Radon Concentration in Pennsylvania, 1989-2013. Environmental Health Perspectives. 123:1130-1137.

  5. Mitchell AL, WM Griffin, and EA Casman. 2016. Lung Cancer Risk for Radon in Marcellus Shale Gas in Northeast U.S. Homes. Risk Analysis. DOI: 10.1111/risa.12570.

  6. Agency for Toxic Substances and Disease Registry. 2012. Tox FAQs for Radon. Accessed August 27, 2015.

  7. U.S. EPA. Indoor Air Quality. Consumer's Guide to Radon Reduction. Accessed August 19, 2016.

Page last updated: February 7, 2022

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