Radon is a radioactive gas. It forms naturally when uranium in soil and rock breaks down. You can’t see, smell or taste it. Outdoors it thins out quickly. Indoors it can build up, because a house tends to pull in soil gas through cracks, gaps around pipes, sump pits and other openings in the foundation [OH-1][EPA-3].
Why it matters
- The EPA estimates radon causes about 21,000 lung cancer deaths a year in the US, about 2,900 of them in people who have never smoked [EPA-1].
- The EPA calls radon the second leading cause of lung cancer overall and the leading cause among non-smokers [EPA-1].
- Smoking and radon together raise the risk much more than either does alone [EPA-1].
How common is high radon?
The EPA estimates that nearly 1 in 15 US homes has an elevated level [EPA-2]. Some areas are much higher. In Ohio, the state health department says about half of all homes tested each year come back elevated [OH-1]. In Pennsylvania’s state test records, about one in three tests in Allegheny County and about half in Lancaster County were at 4 pCi/L or higher [PA-4]. (RadonCosts analysis of PA DEP data. Tests aren’t a random sample of homes.)
Your neighbor’s result doesn’t tell you yours. Two houses on the same street can test very differently. Testing is the only way to know [EPA-2].
Reading your number
Radon in US homes is reported in picocuries per liter of air (pCi/L). (Metric: 1 pCi/L ≈ 37 Bq/m³.)
| Your result | What the EPA says |
|---|---|
| 4 pCi/L or higher | Fix your home. This is the EPA action level [EPA-1]. |
| 2 to 4 pCi/L | Consider fixing. There’s no known safe level, and lower is better [EPA-1]. |
| Below 2 pCi/L | Below the “consider fixing” range. Retest after big changes to the house. |
For context, the EPA puts average outdoor air at about 0.4 pCi/L [EPA-1].
Got one high result? Do this next
The EPA’s step-by-step approach [EPA-2]:
- If a first short-term test is 4 or higher, do a follow-up test.
- Need an answer fast (for example in a home sale)? Do a second short-term test. If the first result was more than twice the action level (8 pCi/L or higher), do the second short-term test right away.
- Not in a hurry? A long-term test (more than 90 days) gives a better picture of your year-round average.
- Fix the home if the average of two short-term tests is 4 or more, or if a long-term test is 4 or more.
What fixing involves
Most homes are fixed with a pipe-and-fan system that pulls radon from under the foundation and vents it above the roofline. The EPA says some systems cut levels by up to 99% [EPA-3]. See how radon mitigation works and what it costs.
Next steps
- Test kits vs professional testing
- Find a certified installer in your state
- How to choose an installer
General information only, not medical advice. Talk to your doctor about health concerns.