The short answer
Radon gas is an invisible, odorless radioactive gas released naturally from soil that is the leading cause of lung cancer in non-smokers. Simple home test kits help keep your home safe.
Radon gas is an invisible, odorless, tasteless radioactive gas created by the decay of natural uranium in soil.
Radon exposure is responsible for an estimated 21,000 lung cancer deaths in the United States every year, and is the #1 cause of lung cancer in non-smokers.
Any home — old or new, with or without a basement — can have elevated radon levels.
Home radon test kits are available, and testing is the only way to know your level.
Watch: The #2 cause of lung cancer is in some homes
52 sec · Captioned · Radon is the #2 cause of lung cancer — testing your home costs under $25.
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This guide is for anyone who wants to protect their household from radon. When people think about lung cancer risk, tobacco smoke usually comes to mind first. But an invisible, odorless gas found naturally in the earth is the leading cause of lung cancer among non-smokers.
That gas is radon. According to the U.S. Environmental Protection Agency (EPA) and the Centers for Disease Control and Prevention (CDC), radon exposure causes an estimated 21,000 lung cancer deaths in the United States each year. Fortunately, you can test your home for radon and fix high levels.
Representative Story Disclosure
This is a representative story created from common experiences described by patients and caregivers. It is not the story of one identifiable person, and individual experiences can differ substantially.
A composite example: Robert and Susan
Robert and Susan, a couple in their early 50s, bought a suburban home in Ohio where they lived for 18 years. Neither had ever smoked, so lung cancer was not on their radar.
They were getting ready to sell their house. During a routine home inspection, the buyer asked for a standard radon test. The test revealed a radon level of 9.4 pCi/L — more than double the EPA's recommended action threshold of 4.0 pCi/L.
Surprised, Susan read up on radon. She learned that breathing high radon levels over many years damages the thin lining of the lungs. The couple immediately hired a certified radon contractor to install an active soil depressurization system. This is a pipe and fan that pull radon from under the house. After installation, a follow-up test showed radon had dropped to 0.9 pCi/L.
Susan reflected:
"We had no idea our home was accumulating invisible radon for 18 years. Getting a mitigation system installed was a relief, for us and for the new buyers."
How radon gets into homes
Radon forms when uranium in rocks, soil, and groundwater slowly breaks down. Because radon is a gas, it moves up through the soil into the air above. From there:
- It rises through the soil under your home.
- It enters through foundation cracks, sump pumps, and joints.
- It gets trapped in the air indoors, where people breathe it in over time.
Radon can enter any home: old or new, insulated or drafty, with a basement or on a slab.
What the EPA numbers mean
Radon levels are measured in picocuries per liter (pCi/L) of air:
- Below 2.0 pCi/L: Lower than the range where EPA suggests considering a fix. EPA says no level of radon is known to be completely safe. Average U.S. indoor radon is about 1.3 pCi/L.
- 2.0 to 3.9 pCi/L: Moderate level. Consider fixing your home, as any radon exposure carries some long-term risk.
- 4.0 pCi/L or higher: EPA Action Level. Fixing your home (mitigation) is strongly recommended to lower lung cancer risk.
How to test your home in three steps
- Get a do-it-yourself test kit. Kits are sold at hardware stores and online retailers. Check that the kit is approved or certified in your state.
- Place the detector. Follow the kit's instructions. NCI notes that radon tends to be higher in basements and first floors, closest to the ground.
- Send it for analysis. EPA says short-term tests stay in the home for 2 to 90 days depending on the device. Charcoal canister kits are left out for 2 to 7 days. EPA adds that a short-term test may not show your year-round average, so a second short-term test can confirm the first.
Radon and smoking together
Radon and tobacco smoke together multiply lung cancer risk far more than either one alone.
EPA's lifetime risk tables put it like this. Of 1,000 people who never smoked and are exposed to 4.0 pCi/L over a lifetime, about 7 could get lung cancer. Of 1,000 people who smoke and are exposed to the same 4.0 pCi/L level, about 62 could get lung cancer — roughly nine times as many, because radioactive particles and tobacco carcinogens act together.
Key takeaways
- Radon is invisible. You cannot see, smell, or taste it.
- It is a leading risk for non-smokers. Radon causes about 21,000 U.S. lung cancer deaths each year.
- Testing is straightforward. EPA says short-term kits stay in place 2 to 90 days depending on the device, and charcoal canisters just 2 to 7 days.
- High levels can be fixed. Homes measuring 4.0 pCi/L or higher should be mitigated by certified contractors.
Frequently asked questions
Short answers to questions people often ask.
Does a neighbor's low radon result mean my house is safe?
No. Radon levels can differ from house to house, so a neighbor's result does not tell you about your home. Test your own home.
How does radon mitigation work?
A certified contractor installs a vent pipe system with an inline fan that pulls radon gas from beneath your foundation and vents it outdoors.
Related resources
- Lung Cancer Risk Factors
- Air Pollution & Cancer Risk
- Carcinogens Overview
- Cancer Prevention Overview
Sources
- U.S. Environmental Protection Agency (EPA): Health Risk of Radon. https://www.epa.gov/radon/health-risk-radon
- U.S. Environmental Protection Agency (EPA): What is EPA's Action Level for Radon and What Does it Mean? https://www.epa.gov/radon/what-epas-action-level-radon-and-what-does-it-mean
- U.S. Environmental Protection Agency (EPA): RadTown Radon Activity 3: Indoor Radon Levels (test durations). https://www.epa.gov/radtown/radtown-radon-activity-3-indoor-radon-levels
- Centers for Disease Control and Prevention (CDC): Radon and Cancer Risk (2025). https://www.cdc.gov/radon
- National Cancer Institute (NCI): Radon and Cancer Fact Sheet (2025). https://www.cancer.gov/about-cancer/causes-prevention/risk/substances/radon
Common questions
How does radon gas enter a home?
Radon moves up through the ground and enters homes through cracks in foundation floors, walls, construction joints, sump pumps, or gaps around pipes.
Can I tell if my home has radon without testing?
No. Radon has no color, odor, or taste. Testing with an approved radon detector is the only way to know if elevated levels are present.
How hard is it to fix a home with high radon levels?
Radon mitigation systems use a vent pipe, often with a fan, to route radon from beneath the home to the outdoors. Ask a qualified radon mitigation contractor how long installation would take for your home.
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Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
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