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How does radon affect human health?

By Radon411 Editorial TeamUpdated How we research

Short answer

Breathing radon at home over a long period raises the risk of lung cancer, the one health effect that is established. The risk grows with the radon level and the length of exposure, and it is much higher for people who smoke.

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

Radon decays into radioactive particles. When these are inhaled they settle on the cells lining the airways, where they can damage DNA and potentially cause lung cancer. Radon is the second leading cause of lung cancer in the United States after smoking and, by EPA's estimates, the leading cause among people who have never smoked.

Any radon exposure carries some risk, and lowering the level reduces the risk of lung cancer. Not everyone exposed to elevated radon develops lung cancer, and the time between exposure and the disease may be many years.

The risk is not one fixed figure for every home. It depends on the concentration in the building, how much time people spend there, and whether they smoke; radon is much more likely to cause lung cancer in people who smoke. This page does not calculate a personal risk figure from a result.

What to do next: test your home, because testing is the only way to know its level. If the result is elevated, a system can bring it down, and a follow-up test confirms it worked. If you have concerns about your own health, talk to a doctor and mention your result.

How radon harms the body, step by step

  1. Radon decays in the air

    Radon escapes from the ground into the air, where it decays and produces further radioactive particles, the short-lived radon progeny.

  2. The particles are breathed in

    Radon progeny often attach to dust, and people take them in mainly by breathing.

  3. They lodge in the lungs

    The particles can get trapped in the lungs and settle on the cells lining the airways.

  4. They give off radiation

    As they break down further they release small bursts of energy; the high-energy alpha particles some decays give off are the main health concern.

  5. Cells are damaged

    That radiation can damage the DNA of the cells lining the lung.

  6. Cancer may follow, years later

    Over a lifetime this damage can lead to lung cancer, and the time between exposure and disease may be many years.

The health effect that is established: lung cancer

What radon does, and does not, do to health
EffectWhat is known
Lung cancerThe only cancer proven to be associated with breathing radon; radon is the second leading cause of lung cancer deaths in the U.S., after cigarette smoke
Other cancers or illnessesNo other cancer risks or other health effects have been established
Other organsInhaled radon delivers some radiation to other organs, but at a much lower level than to the lungs
LeukemiaAn increased risk in adults and children has been suggested, but the evidence is not conclusive
Short-term symptomsNone to watch for; most people have no symptoms until lung cancer is advanced, when it is harder to treat

The link was first noticed in underground uranium miners exposed to radon, who died of lung cancer at high rates. Pooled studies of North American homes later found a slightly increased lung cancer risk with elevated household radon, consistent with the miner studies. Not everyone exposed to elevated radon develops lung cancer. More on the disease is in how does radon cause lung cancer.

What makes the effect larger or smaller

The chance of getting lung cancer from radon depends mostly on how much radon is in your home, how much time you spend there, and whether you smoke or have ever smoked. WHO estimates the risk rises by about 16 percent for every 100 of long-term average radon.

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.
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 1,000What to do
20 pCi/L740 Bq/m³Smoked: About 260Never smoked: About 36Fix your home
10 pCi/L370 Bq/m³Smoked: About 150Never smoked: About 18Fix your home
8 pCi/L300 Bq/m³Smoked: About 120Never smoked: About 15Fix your home
4 pCi/L150 Bq/m³Smoked: About 62Never smoked: About 7Fix your home
2 pCi/L75 Bq/m³Smoked: About 32Never smoked: About 4Consider 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.
EPA's estimate of lifetime lung cancer risk at each radon level, out of 1,000 people, for people who smoked and people who never smoked.
Smoking and age
FactorWhat is known
SmokingSmokers are about 25 times more at risk from radon than non-smokers, by WHO's estimate; radon and smoke together carry a greater risk than either alone
Never smokedBy EPA's estimates, radon is the leading cause of lung cancer among non-smokers, with about 2,900 deaths a year among people who never smoked
ChildrenSmaller lungs and faster breathing may give children higher lung doses, though limited evidence from child miners in China did not show greater susceptibility

Breathing radon and swallowing it

Radon reaches people mainly through the air, but some homes also get it through well water. The lung cancer risk from breathing radon in air is much larger than the stomach cancer risk from swallowing water that holds it, and most of the risk from radon in water actually comes from radon released into the air during showering and other household use.

Two routes into the body
RouteMain concernRelative size
Breathing indoor airLung cancerMuch larger
Swallowing water that holds radonStomach cancerMuch smaller than the lung risk from breathing
Breathing radon released from waterLung cancerMost of the risk from radon in water

Can a doctor test you for radon?

Not in a way that measures exposure. Radon in human tissue is not detectable by routine medical testing. Some radon decay products can be detected in urine and in lung and bone tissue, but those tests cannot tell how much radon you were exposed to or predict whether you will become ill. Exposure is estimated by measuring radon in the air.

Questions about radon and health

What does radon do to your body?

Its decay products lodge in the airways and give off alpha radiation that can damage the cells and DNA there, which over time can lead to lung cancer.

Can radon make you sick right away?

No immediate illness is known. Lung cancer takes many years to develop, and most people have no symptoms until it is advanced. See how long before you get sick from radon.

Does radon cause other cancers?

No other cancer risks or health effects have been established. A link to leukemia has been suggested, but the evidence is not conclusive.

Is radon worse for smokers?

Much worse. Smokers are about 25 times more at risk from radon than non-smokers, by WHO's estimate, and smoking greatly raises the chance of lung cancer at the same radon level.

Does quitting smoking reduce the risk from radon?

Yes. Stopping smoking and lowering your radon level both reduce your lung cancer risk, and not letting others smoke in the house helps too.

Does lowering radon now still help?

Yes. Reducing radon lowers the risk of lung cancer even after living with a radon problem for a long time.

Learn

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