Radon is a radioactive gas that damages the DNA in your lung cells, and over years of exposure, this damage can lead to lung cancer. It’s the second leading cause of lung cancer overall and the number one cause among non-smokers, responsible for roughly 21,000 lung cancer deaths in the United States each year. The tricky part: radon has no smell, no color, and no taste, so you’d never know you were breathing it without testing for it.
How Radon Damages Your Lungs
Radon itself is an inert gas, meaning it doesn’t react chemically with your body. The danger comes from what happens as it breaks down. When radon decays, it produces tiny radioactive particles (called decay products or “progeny”) that cling to dust and aerosols in the air. You inhale these particles, and they lodge in the lining of your lungs.
Once there, these particles emit alpha radiation, a form of energy that’s heavy and slow-moving but extremely destructive at close range. Alpha particles tear through DNA strands in your lung cells, creating what scientists call clustered damage: multiple breaks packed within a tiny stretch of the DNA helix. Your cells have built-in repair machinery for everyday DNA damage, but clustered damage is far harder to fix accurately. Repairs go wrong, mutations accumulate, and over time, a cell can begin dividing uncontrollably. That’s cancer.
This process is slow. There are no immediate symptoms, no coughing, no irritation, nothing that signals you’re being exposed. The lag between exposure and disease is typically 5 to 25 years, which is why radon-related lung cancer often catches people off guard.
Lung Cancer Risk by the Numbers
Your risk depends on two things: how much radon you’re exposed to and how long the exposure lasts. The EPA’s action level is 4 pCi/L (picocuries per liter of air). At that concentration, living in a home for a lifetime carries a meaningful cancer risk, roughly comparable to the risk of dying in a car crash. But the EPA is clear that there is no known safe level of radon exposure, and recommends considering mitigation even at levels between 2 and 4 pCi/L.
If you smoke, radon is far more dangerous. Smoking and radon have a synergistic effect, meaning the combined risk is much greater than you’d get by simply adding the two risks together. The EPA estimates that radon exposure increases lung cancer risk eight to nine times more in smokers than in nonsmokers exposed to the same levels. Cigarette smoke damages the lung lining in ways that make cells more vulnerable to radiation-induced mutations, and radon’s alpha particles compound that damage.
No Warning Signs Until It’s Too Late
Radon exposure produces no immediate symptoms. No headaches, no nausea, no respiratory irritation. You won’t cough more or feel short of breath. This is one of the most important things to understand: your body gives you zero feedback about radon. The only way to know your exposure level is to test the air in your home.
By the time symptoms do appear, they’re symptoms of lung cancer itself: a persistent cough, chest pain, coughing up blood, unexplained weight loss. At that point the disease is already established. Long-term radon exposure has also been linked to chronic, non-cancerous lung conditions like emphysema, pulmonary fibrosis, and chronic interstitial pneumonia, though lung cancer is by far the primary concern.
Some research has explored whether radon might increase the risk of other cancers, particularly leukemia in both adults and children. The American Cancer Society notes that the evidence so far is mixed and much weaker than the lung cancer connection.
Where Radon Comes From in Your Home
Radon forms naturally from the breakdown of uranium in soil and rock. It seeps up through the ground and enters buildings through cracks in foundations, gaps around pipes, sump pits, and any other opening where the house contacts the earth. Every home has some radon. The question is how much.
Radon levels vary enormously from one house to the next, even between neighbors on the same street. Soil composition, foundation type, ventilation, and weather patterns all play a role. The EPA estimates that about 1 in 15 homes in the U.S. has radon at or above the 4 pCi/L action level. Basements and ground floors tend to have the highest concentrations, but upper floors aren’t automatically safe.
Testing Is Simple and Cheap
Short-term radon test kits cost under $20 at most hardware stores and take two to seven days. You place the kit in the lowest lived-in level of your home, leave it undisturbed, then mail it to a lab. Long-term tests (90 days or more) give a more accurate picture of your year-round average, since radon levels fluctuate with seasons and weather. Many state health departments offer free or discounted test kits.
If your results come back at 4 pCi/L or higher, mitigation is the next step. If they’re between 2 and 4, it’s worth considering, especially if you have risk factors like a smoking history or spend a lot of time in lower levels of the home.
How Radon Mitigation Works
The most common and effective fix is called active soil depressurization. A contractor installs a pipe through the foundation slab into the gravel or soil beneath the house, then connects it to a small fan (typically using about 20 watts of power, less than a light bulb) that runs continuously. The fan creates slight negative pressure under the foundation, pulling radon-laden air from beneath the house and venting it safely above the roofline before it can seep indoors.
This system reliably reduces indoor radon levels by 85% or more. Installation typically takes a day and costs between $800 and $2,500 depending on your home’s construction and local labor rates. Once installed, the system runs quietly in the background with minimal maintenance. Most homeowners retest after installation to confirm the levels have dropped below 4 pCi/L, and periodic retesting every few years ensures the system continues working properly.
For new construction, passive radon-resistant features can be built into the foundation from the start, with a fan added later if testing shows elevated levels.