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What Is Radon and What Is the Health Risk? (EPA and CDC)

Updated November 1, 2026 · General information, not medical advice

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What radon is

CDC describes radon as an odorless and invisible radioactive gas naturally released from rocks, soil and water. EPA says it comes from the natural breakdown of uranium found in nearly all soils. It typically moves up through the ground and into a home through cracks and other holes in the foundation, and the home can trap it inside where it builds up.

EPA says any home may have a radon problem: new and old homes, well-sealed and drafty homes, and homes with or without basements. It estimates that nearly 1 out of every 15 U.S. homes has an elevated radon level. Soil gas is the main cause of radon problems. Sometimes radon enters through well water (see radon in well water), and in a small number of homes building materials give off radon.

The health risk

EPA says radon gas decays into radioactive particles that can get trapped in your lungs when you breathe. As they break down further they release small bursts of energy that can damage lung tissue and lead to lung cancer over your lifetime.

• EPA estimates radon causes about 21,000 lung cancer deaths a year in the U.S., with an uncertainty range of roughly 8,000 to 45,000.
• About 2,900 of those deaths are among people who never smoked, EPA says.
• EPA says radon is the second leading cause of lung cancer overall and the number one cause among non-smokers.
• Smoking and radon together are an especially serious health risk. EPA says a smoker also exposed to radon has a much higher risk. If you smoke, stopping and lowering your radon level both reduce your risk.

EPA's lifetime risk tables

EPA estimates the lifetime risk of lung cancer if 1,000 people were exposed to each level over a lifetime.

Source: EPA, Health Risk of Radon, from A Citizen's Guide to Radon. EPA notes that a former smoker's risk may be lower than the smoker column, or higher than the never-smoked column.

EPA says there is some uncertainty about the size of radon health risks, but that we know more about radon risks than risks from most other cancer-causing substances, because estimates are based on studies of cancer in humans (underground miners).

What to do

1. Test. EPA and the Surgeon General recommend testing all homes below the third floor. See test kits.
2. Read the result. Use our checker.
3. Fix a high level. EPA says radon reduction systems work. See how they work.
4. Talk to a doctor about your own health, and follow your state radon program for local rules.

Common questions

What is radon?

CDC calls radon an odorless and invisible radioactive gas naturally released from rocks, soil and water. EPA says it comes from the natural breakdown of uranium in soil, rock and water, and that it can get into the air you breathe.

Is there a safe level of radon?

EPA says no level of radon is safe. It recommends fixing at 4 pCi/L or higher and says to consider fixing between 2 and 4 pCi/L. Levels below 4 pCi/L still pose some risk.

Are children at greater risk?

EPA says children have been reported to have greater risk than adults of certain types of cancer from radiation, but there are currently no conclusive data on whether children are at greater risk than adults from radon.

If I have high radon, will I get lung cancer?

Not necessarily. EPA says not everyone exposed to elevated levels of radon will develop lung cancer, and that the time between exposure and the onset of disease may be many years. Your chances depend mostly on how much radon is in your home, how much time you spend there and whether you smoke or ever smoked.

Related guides

• Radon test kits
• What does my radon test result mean?
• Radon mitigation systems
• Radon in well water
• Are radon levels higher in winter?