What is radon, and why does it matter in Tennessee?
Radon is a radioactive gas that forms naturally when uranium in rock and soil breaks down. You can't see, smell, or taste it. Outdoors it spreads out to harmless levels, but it can seep into buildings and build up. Breathing it over many years raises the risk of lung cancer, and Tennessee's geology makes high indoor levels common.
Key facts
- EPA estimates radon causes about 21,000 lung cancer deaths in the U.S. each year (EPA).
- About 1 in 7 of those deaths are in people who never smoked (American Lung Association).
- 38 of Tennessee's 95 counties are in EPA's highest radon-potential zone.
- Homes needing action have been found in every Tennessee county (Tennessee Radon Program).
Where does radon come from?
Radon comes from the natural decay of uranium, which is found in most rock and soil. As the gas forms, it moves up through the ground. It enters buildings through cracks in floors, joints where floors meet walls, gaps around pipes and cables, sumps, and drains (WHO). TDEC describes a house as acting like a vacuum that draws radon in through these openings. Radon can also come from well water, released into the air when the water is used for showers and other household tasks, as the Tennessee Radon Program notes.
How does radon cause lung cancer?
When radon breaks down, it produces radioactive particles. As we breathe, these particles settle on the cells lining the airways, where their radiation can damage DNA and potentially cause lung cancer (WHO). Radon causes no symptoms, so there's no warning sign until disease develops.
According to EPA, radon is the leading cause of lung cancer among people who have never smoked and the second leading cause overall, after smoking. EPA's best estimate is about 21,000 U.S. deaths a year, with an uncertainty range of 8,000 to 45,000.
Is radon worse for smokers?
Yes, much worse. Smoking and radon each raise lung cancer risk, and together the effect is far larger. EPA estimates that if 1,000 people were exposed to 4 pCi/L over a lifetime, about 62 smokers could get lung cancer compared with about 7 people who never smoked (EPA). Former smokers fall in between.
| Lifetime exposure | Never smoked (per 1,000) | Smokers (per 1,000) |
|---|---|---|
| 20 pCi/L | about 36 | about 260 |
| 10 pCi/L | about 18 | about 150 |
| 4 pCi/L | about 7 | about 62 |
| 2 pCi/L | about 4 | about 32 |
| 1.3 pCi/L (U.S. indoor average) | about 2 | about 20 |
Source: EPA, Assessment of Risks from Radon in Homes, as presented on EPA's health risk page.
Why is radon common in Tennessee?
Radon levels depend mostly on the rock and soil under a building. Tennessee's geology produces high indoor radon in many areas, and the Tennessee Radon Program reports that elevated levels are more common in East Tennessee. Even so, the program has found results calling for action in every county.
EPA's radon zone map places 38 Tennessee counties in Zone 1, meaning their predicted average indoor screening level is above 4 pCi/L. You can look up your county.
Does my county's zone tell me whether my home is safe?
No. EPA built the zone map to help governments plan programs and building codes, and it says the map should not be used to decide whether to test an individual home (EPA Tennessee zone map). Two houses on the same street can have very different levels because of differences in the soil beneath them and how each house is built. The only way to know your home's level is to test it.
How high is radon in Tennessee homes?
There's no statewide random survey to give a true average. The best current indicator is from the state's free test kit program: about 1 in 4 homes that request a kit test above 4 pCi/L, according to the Tennessee Radon Program. Because these are homes whose owners chose to test, this figure isn't a precise statewide rate, but it shows high levels are far from rare.
For comparison, EPA puts the average U.S. indoor level at about 1.3 pCi/L and the outdoor level at about 0.4 pCi/L.
Is any amount of radon safe?
No level is completely risk-free. EPA recommends fixing a home at 4 pCi/L or above and considering a fix between 2 and 4 pCi/L. The World Health Organization recommends a reference level of 100 Bq/m³, about 2.7 pCi/L (WHO). WHO estimates that radon causes 3% to 14% of lung cancers in a country, depending on its average radon levels and smoking rates.
Frequently asked questions
Can I smell or feel radon? No. Radon has no color, odor, or taste, and it causes no immediate symptoms.
Does radon only matter in houses with basements? No. Radon can enter homes built on slabs, crawlspaces, or basements. Levels are usually highest on the lowest floor, but upper floors can be affected too.
Can radon cause cancers other than lung cancer? WHO says no other cancer risks have been established, though inhaled radon delivers a small radiation dose to other organs.
Should I worry about granite countertops? The American Lung Association notes that building materials such as granite are less common sources of radon and rarely cause problems. The soil under your home is the main concern.
Next step: Find out how to test your home →
Sources: U.S. EPA – Health Risk of Radon · EPA – Tennessee Map of Radon Zones · Tennessee Radon Program · TDEC news release, Jan. 2024 · WHO – Radon fact sheet · American Lung Association – Radon
Last reviewed October 17, 2026 by the Tennessee Radon Authority editorial team. How we research.