Short answer
EPA treats 4 pCi/L as the level at which to fix a home, and recommends considering a fix from 2 to 4 pCi/L, but there is no line where radon turns from safe to dangerous. The risk rises steadily with the level, with the years of exposure, and sharply with smoking.
Next step: pick the right test for your home. Which test to use
EPA estimates that out of 1,000 people who never smoked and spent a lifetime at 4
Because a single short-term result can mislead, confirm a high result with a follow-up test before fixing, and take that second test immediately if the first is more than twice the 4 pCi/L
What to do next: if your result is high, confirm it, then plan a fix; if you have not tested, test the lowest lived-in level first.
In a picture · 1 min read
Radon is not divided into safe and dangerous. The U.S. guidance uses one
EPA recommends fixing a home when the radon level is 4 pCi/L or higher. EPA recommends considering a fix when the level is between 2 and 4 pCi/L. The decision should rest on a confirmed number: one
In a picture · 1 min read
EPA estimate, lifetime exposure
| Radon level | Could get lung cancer, per 1,000 | EPA's comparison | What to do |
|---|---|---|---|
| 20 pCi/L740 Bq/m³ | Smoked: About 260Never smoked: About 36 | Smoked: 250 times the risk of drowningNever smoked: 35 times the risk of drowning | Fix your home |
| 10 pCi/L370 Bq/m³ | Smoked: About 150Never smoked: About 18 | Smoked: 200 times the risk of dying in a home fireNever smoked: 20 times the risk of dying in a home fire | Fix your home |
| 8 pCi/L300 Bq/m³ | Smoked: About 120Never smoked: About 15 | Smoked: 30 times the risk of dying in a fallNever smoked: 4 times the risk of dying in a fall | Fix your home |
| 4 pCi/L150 Bq/m³ | Smoked: About 62Never smoked: About 7 | Smoked: 5 times the risk of dying in a car crashNever smoked: The risk of dying in a car crash | Fix your home |
| 2 pCi/L75 Bq/m³ | Smoked: About 32Never smoked: About 4 | Smoked: 6 times the risk of dying from poisonNever smoked: The risk of dying from poison | Consider fixing between 2 and 4 pCi/L |
| 1.3 pCi/L50 Bq/m³ | Smoked: About 20Never smoked: About 2 | Average indoor radon level | |
| 0.4 pCi/L15 Bq/m³ | Smoked: About 3Never smoked: No figure given | Average outdoor radon level |
| Radon level | People who smoked | People who never smoked |
|---|---|---|
| 20 pCi/L | About 260 | About 36 |
| 10 pCi/L | About 150 | About 18 |
| 8 pCi/L | About 120 | About 15 |
| 4 pCi/L | About 62 | About 7 |
| 2 pCi/L | About 32 | About 4 |
Each step up the scale adds risk; there is no cliff edge. Studies of homes put the increase at about 16 percent more lung cancer risk for every 100
At a glance · 1 min read
| First result | What to do |
|---|---|
| Below 2 pCi/L | Lower risk, not none; you may want to test again in the future |
| 2 to 4 pCi/L | Consider a fix; levels below 4 still carry some risk |
| 4 to 8 pCi/L | Take a follow-up test, long-term or a second short-term, before deciding |
| Above 8 pCi/L | More than twice the action level: take a second short-term test immediately |
| Very high readings | Even very high levels can be brought down to acceptable levels; some systems cut radon by up to 99 percent |
A higher first result also makes the decision clearer: the higher your short-term results, the more certain you can be that the home needs fixing. A result near 4 is the least certain; two short-term tests averaging 4.1 pCi/L leave about a 50 percent chance the year-round average is below or above 4. Individual readings are explained on the level pages, such as 8 pCi/L and 10 pCi/L.
At a glance · 1 min read
The chance of getting lung cancer from radon depends mostly on three things, and the level is only the first.
| Factor | Why it matters |
|---|---|
| How much radon is in the home | Risk rises with higher levels of radon |
| How long you spend there | Longer exposure means more risk |
| Smoking | Smokers are about 25 times more at risk from radon than non-smokers, by WHO's estimate; radon combined with smoking is an especially serious risk |
People who never smoked are not exempt. EPA estimates radon causes about 21,000 lung cancer deaths a year, about 2,900 of them among people who never smoked, which makes radon the leading cause of lung cancer among non-smokers by its estimate. The harm is slow: lung cancer takes many years to develop, and not everyone exposed to elevated radon gets it. The health evidence is in the radon lung cancer guide.
Questions · 1 min read
The line for action is 4 pCi/L. There is no separate danger level above it; the risk keeps rising, to about 260 in 1,000 people who smoked and about 36 in 1,000 who never smoked for a lifetime at 20 pCi/L, by EPA's estimate.
Any exposure carries some risk, so harm is a matter of degree. A fix is recommended at 4 pCi/L and worth considering from 2 to 4 pCi/L. See what is a safe level of radon.
It is twice the action level. EPA estimates about 120 in 1,000 people who smoked, and about 15 in 1,000 who never smoked, could get lung cancer from a lifetime at 8 pCi/L. Confirm it with a follow-up test and plan a fix.
EPA's comparison puts a smoker's lifetime risk at 4 pCi/L at about 5 times the risk of dying in a car crash, and a never-smoker's at about the risk of dying in a car crash. At 20 pCi/L the smoker's risk is about 250 times the risk of drowning.
No. Reducing radon lowers the risk of lung cancer even after living with a radon problem for a long time.
Yes. Even very high levels can be brought down to acceptable levels, and most homes can reach 2 pCi/L or below. See how to reduce radon.
How a radon test works, who can run one, and how to read the number it gives you.
How a professional radon test works, what it proves and whether it is worth it.
Read the guideWhat counts as high and how to bring them down.
Read the guideEPA's action level, WHO's reference level and what counts as acceptable.
Read the guide