Lung cancer has been the leading cause of cancer deaths among men since the early 1950s, and in 1987, it surpassed breast cancer to become the leading cause of cancer deaths among women in the United States. Decades later, it remains the deadliest cancer overall. Smoking remains the biggest driver of lung cancer risk, but it is far from the only one. Environmental exposures, especially radon, play a powerful and often overlooked role.
Radon is now recognized as the second leading cause of lung cancer in the U.S., responsible for approximately 21,000 deaths every year. Among people who have never smoked, radon is the number one cause of lung cancer. What makes radon especially dangerous is that you cannot see, smell or taste it. That means many people may be exposed for years without ever knowing it. “While older research reported at least 1 in 15 homes in the U.S. have elevated levels of radon, the State of the Air report has estimated that at least 1 in 5 test results, nearly all from homes without radon reduction systems, are at the U.S. EPA’s action level or above,” said Kevin Stewart, Director of Environmental Health Advocacy at The American Lung Association.
When radon exposure and smoking overlap, the risk of developing lung cancer becomes even greater. To better understand why this combination is so dangerous, let’s look at how lung cancer develops and how radon and smoking damage the lungs separately and together.
How Lung Cancer Develops
Lung cancer begins when cells in the lungs change, or mutate, and start to grow uncontrollably. These abnormal cells can destroy healthy lung tissue and eventually spread to other parts of the body. Most lung cancers are linked to repeated exposure to harmful substances we breathe in. Cigarette smoke is the most well-known example, but radon, air pollution, and occupational exposures can also cause lung damage that leads to cancer. In some cases, lung cancer develops in people without any clear exposure history.
How Radon Causes Lung Cancer
Radon is a naturally occurring radioactive gas that forms when uranium in soil or rocks breaks down. It can seep into homes through cracks in foundations, basement floors, crawl spaces and even contaminate well water. As radon gas decays, it breaks down into radioactive particles that are easily inhaled and can become trapped in the lungs. As these particles continue to decay, they release radiation that damages lung tissue. Over time, this radiation can alter the DNA inside lung cells, increasing the likelihood that those cells will change, or mutate, to become cancerous.
Radon is responsible for about one in seven lung cancer deaths in the U.S. and carries a risk far greater than most other environmental carcinogens regulated by the EPA. It is considered the leading environmental cause of cancer overall. “Though lung cancer caused by radon is usually the result of decades of exposure to even moderate levels, significant exposure to radon, such as high levels over periods as short as five or ten years, is understood to pose an increased risk,” Stewart explained.
How Smoking Causes Lung Cancer
Cigarette smoke contains more than 7,000 chemicals, many of which are known carcinogens, or cancer causing. When these chemicals are inhaled, they directly damage the cells lining the lungs. Smoking increases inflammation in the airways, thickens mucus and clogs breathing passages, making it harder for the lungs to clear out toxins and debris.
Smoking also destroys the cilia, the tiny hair-like structures that line the airways and act as a natural cleaning system for the lungs. Healthy cilia are responsible for sweeping out dust, bacteria and other harmful particles. Cigarette smoke can paralyze or permanently damage these structures, allowing toxic substances to remain in the lungs longer, giving them time cause irreversible damage.
Over time, smoking ravages the alveoli, the tiny air sacs responsible for oxygen exchange. Smoking is linked to about one in three cancer deaths in the United States, and exposure to secondhand smoke causes an estimated 7,300 lung cancer deaths each year.
Understanding the Radon–Smoking Synergy
Radon and smoking are each dangerous on their own, but together the risk is higher than the sum of the effects taken separately. Research shows that for individuals who smoke, the risk of radon-related lung cancer increases about 10 times. This is a risk on top of the background risk from smoking. People who have ever smoked but who do not now do so have a risk level between that for never-smokers and that for current smokers. Smoking damages cilia making it more likely that radioactive radon will invade the lungs and remain lodged there longer. This increases the dose of radiation lung tissue receives and amplifies DNA damage.
“The risk increases so much because smoking damages the lungs’ ability to clear out accumulated radon decay products to certain tissues, worsening the impact of that exposure,” said Stewart. “It’s like being double-teamed in a sport; it’s much harder for the body to handle the combined effects of these two powerful carcinogens.”
Taking Action to Reduce Lung Cancer Risk
The good news is that radon-related lung cancer is preventable. Testing your home for radon is simple and inexpensive, using kits available through the American Lung Association, hardware stores or local health departments. If radon levels are at or above 4 pCi/L, mitigation systems can effectively reduce indoor radon and lower long-term risk.
Avoiding tobacco use remains one of the most powerful steps you can take to protect your lungs from chronic disease and cancer. If you smoke, quitting at any age reduces lung cancer risk, especially when combined with lowering radon exposure. Avoiding secondhand smoke is also critical, particularly in enclosed indoor spaces.
If you have a history of smoking cigarettes, talk with your healthcare provider about lung cancer screening. Low-dose CT scans can detect lung cancer earlier, when treatment is more effective, and should be discussed through a shared decision-making appointment. The U.S. Preventive Services Task Force (USPSTF) recommends annual lung cancer screening with low-dose CT for adults age 50-80 with a 20 pack-year or greater smoking history and who currently smoke or have quit within the last 15 years. For individuals who meet these high-risk eligibility criteria, lung cancer screening is typically covered by Medicare and most private health insurance plans without cost sharing, although coverage can vary by plan. Lung cancer screening based solely on radon exposure, without a smoking history, is not currently recommended by the USPSTF and is generally not covered by insurance. Out-of-pocket costs for screening may range from $100-$400, depending on the facility. Unsure if you qualify for a lung cancer screening or want to learn more about your risk factors? Contact the Lung HelpLine today.
Radon and smoking are a dangerous combination, but awareness, testing, and prevention can save lives. By addressing both risks together, you can take meaningful steps to protect your lung health now and in the future.
Blog last updated: January 14, 2026
