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How long is long-term exposure to radon?

By Radon411 Editorial TeamUpdated How we research

Short answer

There is no set number of years: radon's risk builds with both the level and the time spent breathing it, and EPA describes risk as exposure over a lifetime. A long-term radon test is something different, a measurement that stays in the home for more than 90 days.

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

Your chance of 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. The risk of lung cancer increases proportionally with increasing radon exposure.

The effect is slow. The time between exposure and the onset of lung cancer may be many years, and not everyone exposed to elevated radon will develop it. It is never too late: you reduce your risk when you reduce radon levels, even after living with an elevated level for a long time.

Because exposure adds up, the useful questions are what the level is where you spend most of your time, and how long you have lived there. A of more than 90 days gives a better picture of that year-round level than a of two to 90 days.

What to do next: test the home you live in now. If you have lived for years in a home that was never tested, a test tells you whether to act from here on. If you have health concerns, talk to a doctor and mention the result.

Long-term exposure is measured in years

There is no set number of years that turns radon exposure into long-term exposure. Radon's risk is cumulative. The figures EPA uses describe what would be expected if people were exposed to a given level over a lifetime, and the lung damage radon's decay products cause builds up over the course of a lifetime.

What your chance of lung cancer from radon depends on
FactorWhat it means for exposure
How much radon is in your homeA higher level means more exposure for each year
How much time you spend in your homeMore time at home means more exposure at the same level
Whether you smoke or have ever smokedRadon and smoking act together

Exposure depends on both the level and the time. Many scientists believe that the alpha radiation dose from long-term exposure to elevated levels of radon decay products increases the chance of getting lung cancer.

How risk grows with level and time

The risk of lung cancer increases proportionally with increasing radon exposure; WHO estimates it rises by about 16 percent for each 100 of long-term average concentration. The greater your exposure, especially if you smoke, the greater your chance of lung cancer.

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.
Out of 1,000 people exposed to each level over a lifetime, about how many could get lung cancer, for people who smoked and people who never smoked.

Why the effect takes years to show

The time between exposure and the onset of lung cancer may be many years, and not everyone exposed to elevated radon will develop it. An increased rate of lung cancer was first seen in uranium miners exposed to very high concentrations of radon.

Long-term exposure versus a long-term test

The phrase also names a kind of test. A long-term radon test stays in a home for more than 90 days; a stays two days to 90 days. Because radon levels vary from day to day and season to season, the longer test is the better guide to the year-round average you are actually exposed to.

Exposure and testing: two meanings of long-term
TermMeaning
Long-term exposureBreathing radon over years; the risk builds with level and time
Long-term testA measurement that stays in the home for more than 90 days
Short-term testA measurement of two days to 90 days, depending on the device
Annual averageWhat a long-term test estimates best; a measurement of at least 3 months is preferable

See long-term radon test kits.

Estimating your own past exposure

There is no medical test that shows how much radon you have breathed; tests for decay products cannot tell how much radon you were exposed to. Exposure is estimated by measuring radon levels in the air, so the practical estimate is your home's level and how long you have lived there.

Building a rough picture of your exposure
QuestionHow to answer it
What is the level where I live now?Test the lowest lived-in level
How long have I lived there?Years in the home, and time spent at home each day
What about past homes?Usually unknown unless they were tested
Do I smoke, or did I?Smoking raises the risk at any radon level

Questions about long-term radon exposure

How long does radon exposure take to cause harm?

There is no set time. The time between exposure and the onset of lung cancer may be many years, and the risk grows with both level and time.

Is short-term radon exposure dangerous?

Radon's risk is described over a lifetime of exposure; it is the long-term average level that matters, which is why a long-term test is the better guide.

How many years of radon exposure cause lung cancer?

No number of years is set. Not everyone exposed to elevated radon will develop lung cancer, and the risk rises with exposure.

Does the risk go down after I fix my home?

Yes. You reduce your risk of lung cancer when you reduce radon levels, even after living with an elevated level for a long time.

What is the average radon level people are exposed to?

The average indoor radon level is estimated to be about 1.3 pCi/L.

Can a doctor measure my radon exposure?

No. Tests for decay products cannot tell how much radon you were exposed to. Exposure is estimated from radon levels in the air.

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