Lung cancer is the one established harm from radon, and it comes from breathing the gas over years. The National Cancer Institute (NCI) says “Scientists agree that radon causes lung cancer in humans.” CDC calls radon “the second leading cause of lung cancer deaths in the United States after cigarette smoke.” But none of the CDC, EPA, NCI or World Health Organization (WHO) pages we read lists a symptom of breathing radon, so how you feel can’t tell you your level. A home test can, and the steps are at the end of this page.
This page is general information, not medical advice. Talk to a doctor about symptoms or health worries, and tell them if you smoke or have lived with high radon levels.
If you feel sick at home right now, think of carbon monoxide first, not radon. CDC says its most common symptoms are “headache, dizziness, weakness, upset stomach, vomiting, chest pain, and confusion”. If someone shows signs of poisoning, CDC says to call 911 or Poison Control at 1-800-222-1222, or consult a health care professional, right away.
Read in order, the sections below go from whether the link is real to what to do about it, with a deeper guide along the way. Health statements here come only from CDC (including the ATSDR page on its site), EPA, NCI and WHO. Radon Handbook sells no tests or systems and refers no one.
The link to lung cancer
EPA explains it this way: “Radon gas decays into radioactive particles that can get trapped in your lungs when you breathe. As they break down further, these particles release small bursts of energy. This can damage lung tissue and lead to lung cancer over the course of your lifetime.”
This is slow, and not certain. CDC says “It takes many years for lung cancer to develop”, and EPA says “Not everyone exposed to elevated levels of radon will develop lung cancer.”
The evidence began underground. NCI says radon was identified as a health problem when scientists noted that uranium miners exposed to it “died of lung cancer at high rates”. Researchers then measured radon in homes, and EPA describes a North American study and a European study from 2005 as “definitive evidence of an association between residential radon exposure and lung cancer.”
NCI calls lung cancer “the only cancer proven to be associated with inhaling radon” and says the evidence on leukemia “is not conclusive”. WHO says “No other cancer risks or other health effects have been established to date”. Its word is “established”, not “impossible”.
Our guide to whether radon causes lung cancer sets out the miner and home studies, and what is still uncertain at the low levels in most homes.
How much exposure counts
None of the health agencies we read names a level or a number of years at which radon turns dangerous. EPA says “no level of radon is safe“, and CDC says “There is no known safe level of radon.” What EPA gives instead is a line for action, in pCi/L (picocuries per liter, the usual US unit): “Fix your home if your radon level is 4 picocuries per liter (pCi/L) or higher.” Below that, it says “Radon levels less than 4 pCi/L still pose a risk, and in many cases may be reduced.” So 4 pCi/L is a decision point, not the place where danger starts.
The nearest thing to an answer on “how much” is the table in EPA’s Citizen’s Guide (2025 cover). Each row shows how many people out of 1,000 “could get lung cancer” if exposed to that level over a lifetime.
| Radon level over a lifetime | Per 1,000 who smoked | Per 1,000 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 |
| 1.3 pCi/L (EPA’s average indoor level) | About 20 | About 2 |
These figures describe groups over a lifetime at one level. They aren’t your personal risk, and a few years in a house is a different exposure. EPA notes that a former smoker’s risk “may be lower” than the smokers’ column and “may be higher” than the never-smokers’ column.
Our page on how much radon exposure is dangerous explains how to read the table, what EPA’s model does with time, and why no agency draws a danger line.
Who has the higher risk
CDC lists four things that raise 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, smoking now or in the past, and burning wood, coal or other substances that add particles to the air.
Smoking makes a large difference. CDC says cigarette smoking is linked to about 80% of US lung cancer deaths, and EPA’s Assessment calls the effects of radon and smoking “synergistic”: together they do more harm than either alone. EPA’s table at 4 pCi/L, 62 against 7, is about nine times (our arithmetic), while WHO estimates smokers are 25 times more at risk from radon than non-smokers. Read that as “much higher”, not as one exact multiple.
People who have never smoked aren’t exempt. The figure you’ll see most is about 21,000 deaths a year. It is EPA’s estimate from 2003, based on the 1995 population: 21,100 of 157,400 US lung cancer deaths, or 13.4%, with a 90% range of 8,000 to 45,000. EPA put 2,900 of the 21,100 among never smokers. NCI’s fact sheet, last reviewed in 2011, gives 15,000 to 22,000 a year. EPA’s figure is a modeled estimate, not a count, and it says nothing about one household.
On children, CDC says: “There is not enough data to show whether children have a higher risk of developing lung cancer from radon exposure than adults.”
EPA’s advice covers both risks: “Stop smoking and lower your radon level to reduce your lung cancer risk.” CDC lists a free quit line, 1-800-QUIT-NOW.
What you would notice
People search for “radon poisoning”, but the phrase isn’t on the CDC, EPA, NCI or WHO radon pages we read, and none of them lists short-term symptoms from radon. EPA says you can’t see, smell or taste it. CDC says “Most people don’t have symptoms until lung cancer is advanced and at that point it is harder to treat.” So feeling well tells you nothing about your exposure, and feeling unwell doesn’t point to radon.
Our page on what the agencies say about radon symptoms gives their wording side by side. It also carries CDC’s list of lung cancer symptoms, which is about lung cancer from any cause and is not a list of radon symptoms.
On 4 November 2026 we searched CDC’s, EPA’s, NCI’s and WHO’s main radon pages, plus EPA’s full risk assessment, for the word “headache”. It isn’t in any of them, which is a lack of evidence, not proof of the opposite. Can radon cause headaches? covers what to check first.
If you’ve lived with high radon
Finding a high number after years in a home is unsettling. None of the sources gives a way to work out what those years mean for one person, and we won’t estimate it. EPA says: “It’s never too late to reduce your risk of lung cancer. Don’t wait to test and fix a radon problem.” CDC: “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.”
The sources we read describe testing homes, not people. Talk to a doctor about health worries, and say how long you lived with the level and whether you smoke or used to.
What EPA says to do next
NCI says: “Testing is the only way to know if a person’s home has elevated radon levels.”
- No test yet: “EPA and the Surgeon General recommend testing all homes below the third floor for radon.” Start with how to test for radon.
- You have a number: our radon test result reader gives EPA’s next step for it, and our page on EPA’s radon levels explains where its lines come from.
- A short-term result of 4 pCi/L or higher: EPA says to “take a follow-up test (Step 2) to be sure.“
- Confirmed at 4 pCi/L or higher: EPA says to fix your home. Our guide to radon mitigation systems covers what that involves.
- Between 2 and 4 pCi/L: EPA’s risk table says “Consider fixing”.
Two things worth asking:
- Your doctor: “I’ve lived with radon at about this level for about this many years, and this is my smoking history. Does that change anything you’d suggest?”
- Your state radon office: where can I get a test kit, and how do I find a qualified contractor here?
Sources checked on 4 November 2026.
