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. Then the radon may get trapped inside the house. It 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 there is no basement.

Studies show that nearly 1 out of every 15 homes in the United States has unsafe levels of radon.1, 2 The U.S. Surgeon General and the U.S. Environmental Protection Agency (EPA) recommend that all homes be tested for 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.

How can you find and remove high levels of radon?

You can test for radon using a do-it-yourself test. Use only home tests that are labeled "meets EPA requirements."

You also can hire a qualified tester to do the test. Call the EPA National Radon Hotline at 1-800-SOS-RADON (1-800-767-7236) for help finding a tester.

If tests find a high level of radon, you'll need to reduce it. There are two ways to do this:

  • Prevent radon from entering the building.
  • Vent radon out of the building.

If you hire a company to vent radon from your home or office, make sure the company follows the guidelines set by the EPA. If you live outside the U.S., you can call your regional environmental protection office for more information.

Frequently Asked Questions

Learning about radon:

Testing for radon:

Health effects of radon exposure:

Health Effects of Radon Exposure

When radon starts to decay, very tiny radioactive particles are released. If you inhale these particles, they enter the lungs and may cause cancerous changes in nearby cells. If you breathe in radon, you have a greater chance of getting lung cancer.3

Radon is the second leading cause of lung cancer, second only to tobacco smoke. It is responsible for about 21,000 deaths from lung cancer per year in the United States.1

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

The combination of smoking and radon exposure can greatly increase your risk of developing lung cancer. If you smoke or live with someone who smokes and you live or work in a place with dangerous radon levels, your risk of lung cancer is significantly higher than for someone who has never smoked but lives or works in places with unsafe radon levels. It is never too late to reduce your risk of lung cancer. Don't wait to test for and fix a radon problem. And if you smoke, try to quit. For more information, see the topic Quitting Smoking.

Radon exposure does not produce immediate symptoms. 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.

What Increases Your Risk of Radon Exposure

When uranium decays, it releases radon. Since uranium occurs naturally in soil and rocks, radon is found all over the world. Nearly 1 out of every 15 homes in the U.S. has elevated radon levels.1 Also, if you live or work in an area that has large deposits of uranium (to see a map of the U.S. radon zones, go to the Web site www.epa.gov/radon/zonemap.html), you may be more likely to be exposed to high levels of radon. But factors relating to the specific construction and location of your house may be just as likely to affect your risk of radon exposure as the source of the radon itself. Even houses right next to each other can have very different radon levels.

Radon enters a home or building through cracks in the foundation or walls, through basement floors, and in water supplies (such as private wells). If the water supply contains radon, it may enter the air in the home through faucets, showers, dishwashers, or washing machines. Radon may also enter the home through pipes, sumps, or drains.

Radon is also found in many building materials. But building materials rarely cause a radon problem all by themselves.

Radon is heavier than air, so it is often found in higher concentrations in lower levels of buildings, such as in basements and sumps. Since radon is odorless, tasteless, and invisible, it is wise to test your home and office for radon levels no matter where you live or work.

How to Test for Radon

Testing for radon can be done with a do-it-yourself home test. Use only home tests that are labeled "meets EPA requirements." The two types of home tests used to detect radon are short-term and long-term.

You can purchase an EPA-qualified short-term or long-term detector test kit at hardware or retail stores or through government agencies in the United States, including:

  • Your regional U.S. Environmental Protection Agency. Find your regional office by going to the EPA Web site (www.epa.gov/iaq/whereyoulive.html) or by calling the EPA National Radon Hotline at 1-800-SOS-RADON (1-800-767-7236).
  • The Consumer Federation of America Foundation's Radon FIX-IT Program hotline at 1-800-644-6999.

If you don't want to do the test yourself or if you are buying or selling a home, you can hire a qualified tester to do the testing for you. Contact your state radon office for a list of qualified testers.

  • The short-term test kit stays in your home or office for 2 to 90 days. Radon levels vary daily and from season to season. So you may want to follow up the first short-term test with a second to determine whether reduction in radon is needed.
  • The long-term test kit stays in the home or office for more than 90 days. A long-term test will give more accurate results because radon levels can fluctuate from season to season.

These tests work by measuring average indoor levels of radon in your home or office. Radon is measured in units of radioactivity per volume of air. The most common measure is picocuries per liter of air (pCi/L). The average indoor level of radon is estimated to be about 1.3 pCi/L, while the average outdoor level of radon is about 0.4 pCi/L.1 Levels that equal or exceed 4 pCi/L should be reduced. But the EPA says there is no safe level of radon. Radon levels between 2 pCi/L and 4 pCi/L can be reduced as well. Removing radon sources or venting radon should be done by a contractor specifically trained and certified to fix radon problems.

How to Prevent, Reduce, or Remove Radon

If your home or workplace has a high level of radon, you should take measures to reduce it. The goals of radon reduction are to:

  • Prevent radon from entering the building.
  • Vent or remove radon once it has entered the building.

The most common and usually most effective way to prevent radon from entering the home is through sub-slab depressurization, which involves venting air from beneath the foundation. Another way to remove radon-containing air from a building involves placing heavy plastic over the soil in earth-floored crawl spaces and using a fan and pipes or duct work to vent the radon to the outside (from under the plastic). This technique needs to be performed by qualified contractors who have completed training in a national radon proficiency program. You can locate a qualified contractor by contacting your local EPA office (find your regional office by going to the EPA Web site www.epa.gov/iaq/whereyoulive.html) or by calling the EPA National Radon Hotline at 1-800-SOS-RADON (1-800-767-7236).

The first step in reducing the level of radon in your home or office involves simple venting methods. Contact an EPA-qualified contractor to advise you or help you with ventilation of contaminated areas.

Methods of ventilation can include:4

  • Opening windows.
  • Installing vents in basements or crawl spaces.
  • Increasing air movement with ceiling fans.
  • Venting air outside the house from sump holes or floor drains.

The balance of air exchange is important to properly remove radon from the home or office. This is why it is essential to have a contractor properly trained in radon reduction to help with ventilation procedures.

Other control methods used to reduce radon include sealing cracks in the foundation or walls and using air cleaners.4

Once radon reduction or prevention procedures are done, the home or building should be retested. You may need to retest the home or building more than once until the radon level falls below the acceptable level of less than 4 pCi/L. It is usually safe to continue living in the home or building while the radon is being vented, but you may want to confirm this with your local EPA office.

Helpful Resources

In the United States, you may locate a contractor qualified to remove radon by contacting your local Environmental Protection Agency office (find your regional office by going to the EPA Web site www.epa.gov/iaq/whereyoulive.html) or by calling the EPA National Radon Hotline at 1-800-SOS-RADON (1-800-767-7236). The contractor should be able to show you a certification from a national radon proficiency program demonstrating that he or she has gone through special training to remove or reduce radon levels in your home or office.

Most countries have agencies that provide information about environmental protection. Contact your local environmental agency for more information about radon exposure in your area.

Other Places To Get Help


Agency for Toxic Substances and Disease Registry (ATSDR)
1825 Century Boulevard
Atlanta, GA  30345
TDD: 1-800-232-4636
E-mail: cdcinfo@cdc.gov
Web Address: www.atsdr.cdc.gov

The Agency for Toxic Substances and Disease Registry (ATSDR), an agency of the U.S. Department of Health and Human Services, works to serve the public by using the best science, taking responsive public health actions, and providing trusted health information to prevent harmful exposures and disease related to toxic substances.

American Lung Association
1301 Pennsylvania Avenue NW
Suite 800
Washington, DC  20004
Phone: 1-800-LUNG-USA (1-800-586-4872)
1-800-548-8252 (to speak with a lung professional)
(212) 315-8700
Web Address: www.lungusa.org

The American Lung Association provides programs of education, community service, and advocacy. Some of the topics available include asthma, tobacco control, emphysema, asbestos, carbon monoxide, radon, and ozone.

National Safety Council (NSC)
1121 Spring Lake Drive
Itasca, IL  60143-3201
Phone: 1-800-621-7619
(630) 285-1121
Fax: (630) 285-1315
E-mail: customerservice@nsc.org
Web Address: www.nsc.org/issues/radon/index.htm (for the radon page)

The National Safety Council's mission is to educate and influence society to adopt safety, health, and environmental policies, practices, and procedures that prevent and reduce human suffering and economic losses arising from preventable causes.

Office of Radiation and Indoor Air, Indoor Environments Division, U.S. Environmental Protection Agency
1200 Pennsylvania Avenue NW
Mail Code 6609J
Washington, DC  20460
Phone: 1-800-76-RADON (1-800-767-2366) National Radon Hotline
1-800-55-RADON (1-800-557-2366) National Radon Helpline
Web Address: www.epa.gov/radon

The EPA's Radon Web site provides answers to frequently asked questions regarding the possibility of radon exposure in your home. It also provides a list of hotlines, contact information for regional U.S. EPA offices, and links to other radon resources. The Web site offers access to the publication Consumer's Guide to Radon Reduction, which helps you select a qualified contractor to reduce the radon levels in your home, determine an appropriate radon reduction method, and maintain your radon reduction system. You can also learn how to obtain the video "Breathing Easy: What Home Buyers and Sellers Should Know About Radon."



  1. U.S. Environmental Protection Agency (2007). A Citizen's Guide to Radon: The Guide to Protecting Yourself and Your Family From Radon. Available online: http://www.epa.gov/radon/pdfs/citizensguide.pdf.
  2. American Lung Association (2007). Radon Fact Sheet. Available online: http://www.lungusa.org/site/pp.aspx?c=dvLUK9O0E&b=35420&printmode=1.
  3. Cisek J (2007). Principles of emergency management and management of hazardous materials incidents. In MW Shannon et al., eds., Haddad and Winchester's Clinical Management of Poisoning and Drug Overdose, 4th ed., pp. 1453–1485. Philadelphia: Saunders Elsevier.
  4. U.S. Environmental Protection Agency (2006). Consumer's Guide to Radon Reduction. Available online: http://www.epa.gov/radon/pdfs/consguid.pdf.


Author Maria G. Essig, MS, ELS
Editor Susan Van Houten, RN, BSN, MBA
Associate Editor Tracy Landauer
Primary Medical Reviewer Caroline S. Rhoads, MD - Internal Medicine
Specialist Medical Reviewer R. Steven Tharratt, MD, MPVM, FACP, FCCP - Pulmonology, Critical Care, Medical Toxicology
Last Updated January 29, 2009

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