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Is radon dangerous?

By Radon411 Editorial TeamUpdated How we research

Short answer

Yes. Radon is a known human carcinogen and, after smoking, the second leading cause of lung cancer in the United States, where EPA estimates it causes about 21,000 lung cancer deaths a year. The danger builds over years of breathing it, rises with the level, and is far greater for people who smoke.

Next step: a test is the only way to know your home's level. How to test your home

Radon does not harm you the moment you breathe it. Breathing high levels over time may cause lung cancer, and lung cancer takes many years to develop. The chance of harm depends mostly on the radon level in your home, the time you spend there, and whether you smoke.

Any exposure carries some risk, so the useful question for a household is not whether radon is dangerous in general but how high the level is at home.

What to do next: test the lowest lived-in level of your home, and if the result is high, plan a fix; a system lowers the level and the risk with it.

How dangerous radon is, in numbers

Radon's danger is lung cancer, and across a whole population it is large. Radon is a cancer-causing radioactive gas and the second leading cause of lung cancer in the United States; only smoking causes more lung cancer deaths.

Radon and lung cancer: the published estimates
EstimateFigure
EPA's estimate of radon-related lung cancer deaths in the U.S. each yearAbout 21,000
Of those, EPA's estimate of deaths among people who never smokedAbout 2,900
The National Cancer Institute's range of U.S. estimates15,000 to 22,000 a year
WHO's estimate of the share of all lung cancers caused by radon, by countryBetween 3% and 14%
Radon's rank among causes of lung cancer in non-smokers, per EPANumber one

For most people radon is also the single greatest environmental source of radiation exposure, and nearly 1 in 15 U.S. homes is estimated to have elevated levels.

Why the risk is well established

Radon's risk rests on human evidence, not only on laboratory animals. It is classified as a known human carcinogen by the major U.S. and international health authorities. The largest study of underground miners covered 68,000 underground miners, who were dying of lung cancer at 5 times the expected rate, and the miners' risk has been documented at exposures comparable to those that occur in homes.

The kinds of evidence behind radon's risk
EvidenceWhat it showed
Underground minersUranium miners exposed to radon died of lung cancer at high rates, which first identified radon as a health problem
Studies of homesPooled North American studies found a slightly increased lung cancer risk with elevated household radon, consistent with the miner studies
Low household levelsStudies in Europe, North America and China confirmed that even the low concentrations common in homes carry health risks
CertaintyMore is known about radon's risks than about most other cancer-causing substances, because the estimates rest on studies of people

Who is most at risk

The chance of getting lung cancer from radon depends mostly on how much radon is in the home, how much time you spend there, and whether you smoke or have smoked. The same level is far more dangerous for some people than for others.

Who faces more risk
WhoWhy
People who smokeSmokers are about 25 times more at risk from radon than non-smokers, by WHO's estimate; smoking plus high radon makes the risk especially high
People who never smokedRadon is the leading cause of lung cancer among non-smokers, by EPA's estimate, and more than 10 percent of radon-related cancer deaths occur among nonsmokers, by NCI's
ChildrenThey may take in higher doses than adults at the same level because they breathe faster and their lungs differ, though there is not enough data to show their lung cancer risk is higher
People who burn wood or coal indoorsBurning wood, coal or other fuels that add particles to the air is one of the factors that raise radon risk
Bar chart of EPA's radon risk estimates for people who smoked and people who never smoked: out of 1,000 people exposed over a lifetime, about how many could get lung cancer at 20, 10, 8, 4, 2, 1.3 and 0.4 pCi/L, from about 260 smokers at 20 pCi/L to about 3 at 0.4 pCi/L, with EPA's advice at each level and its comparison to other risks.
Read this figure as text

EPA estimate, lifetime exposure

  • Out of 1,000 people who smoked
  • Out of 1,000 people who never smoked
About how many people out of 1,000 exposed over a lifetime could get lung cancer, by radon level
Radon levelCould get lung cancer, per 1,000EPA's comparisonWhat to do
20 pCi/L740 Bq/m³Smoked: About 260Never smoked: About 36Smoked: 250 times the risk of drowningNever smoked: 35 times the risk of drowningFix your home
10 pCi/L370 Bq/m³Smoked: About 150Never smoked: About 18Smoked: 200 times the risk of dying in a home fireNever smoked: 20 times the risk of dying in a home fireFix your home
8 pCi/L300 Bq/m³Smoked: About 120Never smoked: About 15Smoked: 30 times the risk of dying in a fallNever smoked: 4 times the risk of dying in a fallFix your home
4 pCi/L150 Bq/m³Smoked: About 62Never smoked: About 7Smoked: 5 times the risk of dying in a car crashNever smoked: The risk of dying in a car crashFix your home
2 pCi/L75 Bq/m³Smoked: About 32Never smoked: About 4Smoked: 6 times the risk of dying from poisonNever smoked: The risk of dying from poisonConsider fixing between 2 and 4 pCi/L
1.3 pCi/L50 Bq/m³Smoked: About 20Never smoked: About 2Average indoor radon level
0.4 pCi/L15 Bq/m³Smoked: About 3Never smoked: No figure givenAverage outdoor radon level
  • Smoked: If you are a former smoker, your risk may be lower.
  • Never smoked: If you are a former smoker, your risk may be higher.
  • Reducing radon levels below 2 pCi/L (75 Bq/m3) is difficult.
  • Lifetime risk of lung cancer deaths, as EPA estimates it.
  • The risk comparisons are EPA's.
EPA's estimate of lifetime risk at each radon level for people who smoked and who never smoked, compared with other risks.

What kind of danger it is

Radon is not an immediate poison. Breathing high levels over time may cause lung cancer, and lung cancer takes many years to develop. Most people have no symptoms until the cancer is advanced and harder to treat, which is why testing matters more than waiting for signs. Not everyone exposed to elevated radon develops lung cancer.

What radon does and does not do
QuestionAnswer
Does it cause other cancers?No other cancer risks or health effects have been established; lung cancer is the only cancer proven to be linked to breathing radon
Is outdoor radon a danger?Outdoors, radon quickly dilutes to very low levels and is generally not a problem
Is any level free of risk?No; any exposure carries some risk, and there is no known safe level

How the harm happens in the body is covered in how does radon affect human health, and the full evidence in the radon lung cancer guide.

Questions about the danger of radon

How dangerous is radon at the 4 pCi/L action level?

EPA estimates that out of 1,000 people who smoked and spent a lifetime at 4 pCi/L, about 62 could get lung cancer, and about 7 of 1,000 who never smoked. Its comparison puts the smoker's risk at about 5 times the risk of dying in a car crash. See what radon level is dangerous.

Is low-level radon dangerous?

Less so, but not risk-free. Even the low concentrations common in homes carry some health risk, and any exposure carries some risk.

Is radon more dangerous than smoking?

No. Smoking causes more lung cancer deaths, and radon is second. The two together are worse than either: radon combined with smoking is an especially serious health risk.

Is radon dangerous for children?

Children may take in higher doses than adults at the same level, though there is not enough data to show whether their lung cancer risk is higher.

I have lived with radon for years. Is it too late to act?

No. Reducing radon lowers the risk of lung cancer even after living with a radon problem for a long time.

Can a dangerous radon level be fixed?

Yes. Even very high levels can be brought down to acceptable levels. See how to reduce radon.

Learn

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