Radon lung cancer risk

That warning comes from the national health advisory U.S. Surgeon General Richard H. Carmona issued in January 2005, which EPA reprints in its Citizen's Guide. The advisory's own text is blunt: more than 20,000 Americans die of radon-related lung cancer every year, and if you also smoke, your risk of lung cancer is much higher. It told Americans to test their homes and, at a level of 4 pCi/L or more, to take steps to remedy the problem as soon as possible.

EPA's Home Buyer's and Seller's Guide gives the short version: you cannot see, smell or taste radon, and when you breathe air containing radon, you increase your risk of getting lung cancer. EPA's Citizen's Guide calls it a cancer-causing, radioactive gas. The danger is not a sudden illness but a long-term rise in the chance of one disease.

The major human health problem related to radon accumulation is lung cancer

WHO describes radon as one of the leading causes of lung cancer and a major cause of lung cancer. EPA's Health Risk of Radon page lists smoking, radon and secondhand smoke as the leading causes of lung cancer, with smoking first, radon second, and secondhand smoke third at an estimated 3,000 lung cancer deaths every year. Radon accumulates indoors because, as EPA explains, the home traps it inside, where it can build up; outdoors, WHO notes, it quickly dilutes to very low concentrations. NCI adds that in areas without adequate ventilation, such as underground mines, radon can accumulate to levels that substantially increase the risk of lung cancer.

How does radon cause lung cancer?

1. 1

   Radon decays in indoor air

   WHO: radon escapes from the ground into the air, where it decays and produces further radioactive particles. NCI: radon decays quickly, giving off tiny radioactive particles.

2. 2

   The particles are breathed in

   WHO: as we breathe, these particles are deposited on the cells lining the airways. CDC: radioactive particles from the decay of radon gas can get trapped in your lungs.

3. 3

   They release energy

   EPA: as the particles break down further, they release small bursts of energy. ATSDR: some of the decays expel high-energy alpha particles, which are the main source of health concerns.

4. 4

   Cells are damaged

   EPA: this can damage lung tissue. WHO: the particles can damage DNA and potentially cause lung cancer. NCI: when inhaled, these radioactive particles can damage the cells that line the lung.

5. 5

   Disease may follow years later

   EPA: this can lead to lung cancer over the course of your lifetime. Not everyone exposed to elevated levels of radon will develop lung cancer, and the time between exposure and the onset of the disease may be many years.

Radon decay products

The radioactive particles radon produces as it decays in the air, which ATSDR calls radon progeny: radioactive atoms with short half-lives into which radon quickly decays. These are what WHO describes being deposited on the cells lining the airways, and what CDC describes getting trapped in the lungs.

What type of radiation is radon?

Alpha radiation. ATSDR explains that when radon or its progeny decay, some of the decays expel high-energy alpha particles, and that the main isotope of health concern is radon-222. In ATSDR's words, many scientists believe that the alpha radiation dose from long-term exposure to elevated levels of radon progeny in air increases your chance of getting lung cancer. The radon element guide covers the decay chain itself.

The evidence began with miners. NCI says radon was identified as a health problem when scientists noted that underground uranium miners who were exposed to it died of lung cancer at high rates, and WHO says an increased rate of lung cancer was first seen in uranium miners exposed to very high concentrations of radon. NCI adds that the results of miner studies have been confirmed by experimental animal studies, which show higher rates of lung tumors among rodents exposed to high radon levels.

What the home studies found

The question was whether miners' results applied to ordinary homes, where levels are far lower. In the home studies NCI describes, scientists compare radon levels in the homes of people who have lung cancer with those of people who have not. Researchers have combined and analyzed data from all radon studies conducted in Canada and the United States; the results demonstrated a slightly increased risk of lung cancer for individuals with elevated exposure to household radon, and that increased risk was consistent with the estimated level of risk based on studies of underground miners. WHO adds that studies in Europe, North America and China have confirmed that even low concentrations of radon, such as those commonly found in homes, pose health risks. On the 2005 pooled studies, EPA quotes the former director of its Indoor Environments Division, Tom Kelly:

Who classifies radon as a cause of cancer

ATSDR states that the Department of Health and Human Services, the International Agency for Research on Cancer (IARC) and EPA all consider radon to be a human carcinogen. IARC's list of classifications by cancer site places radon-222 and its decay products among the carcinogenic agents with sufficient evidence in humans for the lung. EPA's 2003 assessment opens by noting that radon has been classified as a known human carcinogen. NCI sums up where the science stands: scientists agree that radon causes lung cancer in humans.

Each figure is given as published. The estimates differ because they come from different models and years; none is a count of death certificates.

Radon gas lung cancer deaths in the United States

EPA's figure rests on the National Academy of Sciences' BEIR VI report of 1999, which EPA calls the most definitive accumulation of scientific data on indoor radon and which confirmed radon as the second leading cause of lung cancer in the U.S. In 2003 EPA updated its risk estimates from that report, working with its Science Advisory Board, and arrived at a best estimate of about 21,000 annual lung cancer deaths from radon, with an uncertainty range of 8,000 to 45,000. CDC cites the EPA and Surgeon General estimate as more than 21,000 lung cancer deaths each year.

What WHO's figures add

WHO's estimate that radon causes 3% to 14% of all lung cancers in a country explains why the share differs from place to place: it depends on the national average radon level and on how common smoking is. WHO also describes how risk scales with concentration. Under the model WHO describes, the risk falls in proportion as the concentration falls, so a lower level carries a lower risk rather than none.

EPA publishes a chart that turns its risk model into lifetime numbers at different radon levels, separately for people who have never smoked and people who smoke. Each row is EPA's estimate for 1,000 people exposed to that level over a lifetime, from its 2003 Assessment of Risks from Radon in Homes.

The same chart as percentages, with the general population

Appendix D of EPA's 2003 assessment prints the underlying lifetime risks as percentages, and adds a column for the general population. It assumes constant lifetime exposure in homes at each level.

Read this figure as textHide the text version

2 pCi/L

4 pCi/L

00 Bq/m³274 Bq/m³4148 Bq/m³6222 Bq/m³8296 Bq/m³10+370 Bq/m³

• Below 2 pCi/L (below 74 Bq/m³)Below both of EPA's guidance levels.
• 2 to 4 pCi/L (74 Bq/m³ to 148 Bq/m³)EPA recommends considering a fix when the level is between 2 and 4 pCi/L.
• At or above 4 pCi/L (148 Bq/m³ and up)EPA recommends fixing a home when the radon level is 4 pCi/L or higher.

The chart also shows why EPA says radon levels below 4 pCi/L still pose a risk: the rows under the action level do not fall to zero. EPA's guidance follows from that. 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. To place your own result on the scale, use the result interpreter or read what radon levels mean.

EPA's chart sets each radon level beside a familiar risk.

EPA's Health Risk of Radon page adds why lung cancer weighs so heavily: from the time of diagnosis, between 11 and 15 percent of those afflicted will live beyond five years. NCI puts radon in proportion: cigarette smoking is the most common cause of lung cancer, and radon represents a far smaller risk for this disease, but it is the second leading cause of lung cancer in the United States.

Smoking is the leading cause of lung cancer, EPA says, and radon the second. CDC is specific: cigarette smoking is the number one risk factor for lung cancer, it is linked to about 80% of lung cancer deaths in the United States, and people who smoke cigarettes are 15 to 30 times more likely to get lung cancer or die from it than people who do not smoke. Among people who do not smoke, radon moves to first place: EPA estimates it is the number one cause of lung cancer among non-smokers. CDC adds that radon can cause lung cancer in people who have never smoked cigarettes.

The two exposures are not simply added together. EPA's 2003 assessment concluded that the effects of radon and cigarette smoking are synergistic, so that smokers are at higher risk from radon. NCI puts it the same way: exposure to the combination of radon gas and cigarette smoke creates a greater risk of lung cancer than exposure to either factor alone.

WHO estimates smokers are 25 times more at risk from radon than non-smokers; CDC says people who smoke have a 10 times greater risk of lung cancer from the same radon levels. EPA's 2003 assessment adds a subtlety: the excess relative risk is about twice as high for never smokers, but since ever smokers have a much higher baseline lung cancer rate, their absolute risk from radon is still much higher. So never smokers owe a larger share of their lung cancers to radon, while smokers account for most of the deaths.

• EPA: stop smoking and lower your radon level to reduce your lung cancer risk.
• CDC: if you smoke, quitting is still the best way to reduce your risk of lung cancer, and a person's risk of getting lung cancer goes down after they quit.
• CDC: smoking and secondhand smoke, combined with high radon levels, increase your risk; not smoking and not allowing others to smoke in your house helps prevent lung cancer.
• CDC also lists burning wood, coal or other substances that add particles to the air as a factor that increases the risk from radon.
• CDC's free support line for quitting is 1-800-QUIT-NOW.

There is no known threshold, a number of years after which radon causes cancer. The risk builds with the level and the time spent breathing it. EPA says your chances of getting lung cancer from radon depend mostly on how much radon is in your home, the amount of time you spend in your home, and whether you are a smoker or have ever smoked. CDC says it takes many years for lung cancer to develop, and that most people don't have symptoms until lung cancer is advanced, when it is harder to treat.

How long does it take radon to cause cancer?

Years, and often decades. EPA's Citizen's Guide says the amount of time between exposure and the onset of the disease may be many years. The 5-year figure above is a modelling assumption about the shortest delay, not a prediction that cancer follows after five years. EPA's risk figures are lifetime estimates, which is why testing and lowering a high level sooner means fewer years at that level.

People ask whether radon causes other cancers. NCI's answer is that lung cancer is the only cancer proven to be associated with inhaling radon, and WHO's is that no other cancer risks or other health effects have been established to date, although inhaled radon can deliver radiation to other organs, at a much lower level than to the lungs. The table sets out what is established for each, including the questions that remain open.

Radon in water raises a separate question about the stomach. EPA says your risk of lung cancer from breathing radon in air is much larger than your risk of stomach cancer from swallowing water with radon in it, and that most of the risk from radon in water comes from radon released into the air. See radon in water. The stroke and COPD findings are research associations that NIEHS reports, not established effects.

Radon effects on humans: who is most exposed

WHO says that for most people the greatest exposure to radon occurs in the home, where people spend much of their time, though indoor workplaces can also be a source. CDC lists what raises the risk of lung cancer from radon: high levels in your home or another building you regularly spend time in, high levels in the part of the building where you spend the most time (often basements and lower levels), smoking now or in the past, and burning substances that add particles to the air.

On children, CDC says there is not enough data to show whether they have a higher risk of lung cancer from radon than adults, and EPA's Citizen's Guide says there are currently no conclusive data either way. ATSDR puts the general rule plainly: the greater your exposure to radon, especially if you smoke cigarettes, the greater your chance of developing lung cancer.

For the wider debate about whether radon risk is overstated, including the county-level study that some cite against it, see is radon a scam?.

EPA's Citizen's Guide states the principle: since there is no known safe level of radon, there can always be some risk, but the risk can be reduced by lowering the radon level in your home. CDC puts it more directly still: reducing radon inside your home or building will always help reduce your risk of lung cancer, even when the level in your home is less than 4 pCi/L. And EPA says it is never too late to reduce your risk of lung cancer.

1. 1

   Test

   Testing is the only way to know the radon level in a specific building. Test the lowest lived-in level with a short-term test of at least 48 hours under closed-house conditions, or a long-term test of more than 90 days. See how to test for radon.

2. 2

   Confirm a high result

   EPA recommends following a first short-term result at or above the action level with a long-term test, or a second short-term test if you need results quickly.

3. 3

   Fix

   EPA says the method primarily used is a vent pipe system and fan that pulls radon from beneath the house and vents it outside, and that some systems reduce radon levels by up to 99%. Use a contractor trained to fix radon problems; the directory lists mitigation professionals.

4. 4

   Retest

   Test again after the work to be sure radon levels have been reduced, and retest every two years to be sure they remain low.

EPA's 2003 assessment explains why fixing the highest homes matters most but is not the whole story: it is not feasible to totally eliminate radon from the air, and it cites an estimate that about one-fourth of the radon-related lung cancers could be averted by reducing radon in homes that exceed the 4 pCi/L action level. WHO notes that well-tested, durable and cost-efficient methods exist for preventing radon entry into new buildings and reducing radon in existing ones. For what a fix involves, see radon mitigation; for area data as context before you test, see the radon map.

• Test the lowest lived-in level of your home, and test again if you start using a lower floor. See how to test.
• Read the result against EPA's two marks with the interpreter.
• Confirm a first high short-term result before you decide, as EPA recommends.
• If the level is high, get a mitigation system from a trained contractor and retest afterward.
• If anyone in the home smokes, quitting lowers the risk from radon and from smoking at once (CDC, 1-800-QUIT-NOW).
• Retest every two years, and after any structural change or move, as the Surgeon General's advisory asks.