Of all the cancers you could get, lung cancer has some of the most easily identifiable risk factors—including a big one that's completely in your control to eliminate. Learn what experts say you can do to reduce your risk of this disease.
In some ways, lung cancer is more straightforward than other cancers—at least in terms of what causes the disease. It’s well-known that smoking tobacco is the number-one driving force behind most cases. But what many people don’t realize is that anyone with lungs can get lung cancer. That includes never-smokers, people with a genetic hiccup, those exposed to cancer-causing agents, and even individuals who’ve already dealt with a different type of cancer in the past. We asked leading lung cancer experts in the U.S. to share what’s known about the causes of this condition—with the hope of keeping you healthy.
We went to some of the nation’s top experts in lung cancer to bring you the most up-to-date information possible.
Jacob Sands, M.D.Thoracic Medical Oncologist and Instructor in Medicine
Matthew Schabath, Ph.D.Epidemiologist and Thoracic Oncologist
Elisabeth Dexter, M.D.Thoracic Surgeon and Quality Assurance Officer for the Department of Thoracic Surgery
What Is Lung Cancer, Exactly?
In a nutshell, lung cancer begins when the DNA in a single cell or cells in your lungs mutates and causes cells to begin growing abnormally. As those cells multiply, that DNA glitch does as well. Eventually, these abnormal cells cluster together to form a mass or tumor. As the tumor grows, it cuts off the supply of oxygen to the remaining healthy lung tissue, eventually destroying it and taking over your lungs. In addition to making it difficult to breathe, lung cancer also makes the act of moving oxygen throughout the body exceedingly more difficult.
Lung cancer is the second-most common cancer in both men and women in the U.S. More than 228,000 Americans are diagnosed with lung cancer each year, accounting for about 13% of all new cancer cases. The disease is usually classified as either the slower-growing non-small cell lung cancer (NSCLC) or small cell lung cancer (SCLC), which tends to grow and spread faster.
Smoking tobacco is far and away the biggest risk factor for developing lung cancer. In the U.S., smoking causes roughly 90% of all lung cancer cases in men and approximately 80% of all lung cancers in women, according to the National Cancer Institute. That’s largely due to the dangerous chemicals found inside the typical cigarette.
You might think that means nicotine, but while nicotine is the addictive chemical that keeps smokers coming back for more, it does not cause lung cancer. So, what does? There are literally thousands of chemicals that go into making cigarettes, and 250 of them known to be harmful. Of those 250, 69 have been proven to cause cancer, including formaldehyde, arsenic, and chromium, each of which is classified as a carcinogen.
Those carcinogens are found in the smoke you inhale, and when they are drawn into the lungs, they cause cells to mutate and grow erratically, leading to lung cancer. In fact, research in the journal Science estimates that smoking one pack of cigarettes per day for a year causes 150 separate mutations in lung cells. And it’s not just heavy smoker who are upping their lung cancer risk: Smoking even just one cigarette a day over a lifetime can cause lung cancer, notes a 2017 report in JAMA Internal Medicine.
With all of that to consider, it’s puzzling that many smokers continue to puff away. According to a report in the journal Addictive Behaviors, 34% of smokers did not associate a 10-cigarettes-a-day habit with any risk of lung cancer. In addition, only half of current smokers surveyed considered themselves to be at a higher risk of lung cancer than the average non-smoking population. Think of it this way: If you smoke, it’s like driving the family sedan at 100 miles an hour on a curvy road. You might not crash, but you probably will—and if you do, it’s going to be a bad one. Nonsmokers, on the other hand, are like the careful, speed-minding drivers. They are less likely to crash the family car, but there is still some risk.
Is Secondhand Smoke a Big Risk Factor?
According to the most recent data from the Centers for Disease Control and Prevention, nonsmokers exposed to secondhand smoke either at home or at their place of employment have an increased risk of lung cancer risk of 20% to 30%. But the truth is, it’s hard to quantify the risk of passive smoke.
Here’s what we know: Secondhand smoke is bad for your lungs. Secondhand smoke is also considered a carcinogen by the Environmental Protection Agency and the U.S. Surgeon General. While exposure to secondhand smoke is not the same as smoking cigarettes, it is also not the same as having zero exposure. The more secondhand smoke you breathe, the more carcinogens your lungs inhale and absorb.
What Is the Second-Leading Cause of Lung Cancer?
Despite raising your risk factor by up to 30%, exposure to passive smoke is not the second-leading cause of lung cancer in the U.S.—exposure to radon is.
Radon is a colorless, tasteless, odorless, radioactive gas that’s naturally found in decaying uranium, thorium, and radium in rocks and soil. Radon exposure is the leading cause of lung cancer for nonsmokers and it’s responsible for an estimated 15,000 to 22,000 lung cancer deaths in the U.S. each year. Even so, the majority of radon-related lung cancer deaths still occur among those who smoke. (Only 10% of radon-related lung cancer deaths occur among nonsmokers.)
Because radon is a naturally occurring gas, very low levels are present in nearly all the air we breathe. It’s not considered dangerous unless it collects in building structures without good ventilation, like underground mines or basements with cracks in the foundation that allow radon to seep in through the ground but lack enough ventilation to release it to the outside. In places with poor ventilation, the gas can be inhaled at higher quantities where it can damage lung cells, leading to lung cancer.
The only way to know if your home contains has high levels of radon is to get your levels tested. It’s a fairly easy and inexpensive test to do—and it’s recommended that all homeowners arrange for one. You can purchase a radon test kit at a local home improvement store or online via the American Lung Association.
If you find your home has a reading of 4.0 pCi/L of radon or greater, you should talk with your local environmental agency about having a radon mitigation system installed—a fancy way of saying that you need a pro to put in a vent pipe and fan, and then properly seal cracks in the walls, floors, and foundation. (The EPA advises considering changes at even lower levels of between 2 and 4.0 pCi/L.)
What Other Chemicals Cause Lung Cancer?
Workplace chemicals that have been linked to lung cancer include:
Some petroleum products
It’s very likely that a cumulative exposure to these substances coincides with your risk of lung cancer. The actual way they interact with your lungs differs by chemical: For instance, when inhaled, asbestos fibers can become lodged in lung tissue, causing inflammation, scarring, and cellular damage that eventually leads to cancer. Meanwhile inhaling arsenic may caused cancerous changes on a chromosomal level.
The bottom line for any of these chemicals: The greater your exposure, the higher your risk. It’s thought that occupational exposure to lung cancer-causing agents contributes to anywhere between 6 and 17% of lung cancer cases in men in the U.S., notes a study in the American Journal of Industrial Medicine. And if you are a smoker who is regularly subjected to these chemicals, your chances of lung cancer are even higher.
Does Pollution Cause Lung Cancer?
Pollution can play a role in lung cancer. Specifically, particle pollution, which is when very, very small—smaller than a grain of sand—solid and liquid particles mix together and are present in the air, ready to be inhaled. The tiny size is key, because small particles can easily be trapped in the lungs, causing inflammation and DNA damage.
These potentially cancer-causing particles can be emitted from things like wood stoves, vehicles, wildfires, power plants, and more. In the U.S, it’s thought that about 10,000 lung cancer deaths are in some way attributable to air pollution annually, which accounts for about 6% of all lung cancer deaths. (For world perspective, pollution is associated with 223,000 lung cancer deaths globally each year.)
What Role Does Genetics Play?
In the majority of lung cancer cases, genetic mutations that damage DNA are collected over a person's life by way of exposure to, say, tobacco or radon. These changes are called somatic mutations. They aren’t inherited, and they are only found in the lungs.
In some cases, however, genetic changes can be inherited. These are called germline mutations, and they’re fairly rare. Even so, just because you inherit an increased risk of lung cancer, that doesn’t necessarily mean that you will develop the disease. Right now, it is unknown exactly how many lung cancer cases are connected to genetics or “bad genes” that gets passed down from a parent.
In most cases, when experts talk about genetics and lung cancer, it’s in reference to never-smokers who have experienced a seemingly random mutation. The gene changes that may be found in never-smokers with lung cancer include EGFR (epidermal growth factor receptor) mutations and ROS1 (receptor tyrosine kinase) and ALK (anaplastic lymphoma kinase) fusions. The EGFR mutation, for instance, is present in about 10% of non-small cell lung cancers—and it’s found in nearly half of all never-smokers with NSCLC.
Other Causes of Lung Cancer
There are a few other risk factors for this disease, including people with a history of chronic obstructive pulmonary disease (COPD), which includes chronic bronchitis and emphysema. If you fall into this group, you have a two- to fivefold greater risk of developing lung cancer than smokers without COPD. Your outcomes after lung cancer treatment are also worse. (It’s thought that, in part, COPD increases oxidative stress, thus damaging DNA in the lungs and making it more likely that mutations leading to cancer will occur.)
Another lung cancer risk factor: Radiation therapy due to a prior cancer. Women who undergo radiation therapy for breast cancer have a small but significant increased risk of developing lung cancer, notes a study in the journal Radiotherapy & Oncology.
That risk is also present for other cancer survivors who experienced radiation therapy to the chest area. (Smoking increases your risk of lung cancer after radiation even more.) All in all, however, your risk of developing lung cancer from radiation treatments is still relatively small, and the potential future risk is usually no match for the benefit of treating the initial cancer.
One of the most important things to know about lung cancer is that your fate is very much in your hands. By far, smoking cigarettes is the greatest risk factor for the disease, and whether or not you smoke is your decision. And while exposure to workplace chemicals may not be something you can control, being aware of the possibility gives you the chance to ask your company about the materials you are working with, and if something concerns you, you can reach out to organizations like the U.S. Occupational and Safety Health Administration for advice. Ultimately, if you do develop lung cancer, regardless of the cause, there is reason for hope: New and better treatments are being developed every day.
Frequently Asked QuestionsLung Cancer Causes
Can I reduce my lung cancer risk if I quit smoking?
Yes. Heavy smokers who kick the habit have a 39% lower risk of lung cancer within five years of quitting than those who continue smoking, notes a study in the Journal of the National Cancer Institute. Plus, your risk continues to fall with each passing year after quitting.
How do I know if I’m exposed to radon?
You can—and should—test your home for radon. Test kits can be found at your local home improvement store, through the American Lung Association. If you prefer, you can also hire a certified radon-testing professional. Find one through your state radon program.
When it comes to lung cancer risk, how dangerous is social smoking?
Even one cigarette a day over your lifetime can cause lung cancer, according to studies. Women between the ages of 35 and 49 who smoke one to four cigarettes a day are five times more likely to develop lung cancer than their non-smoking counterparts. For men, that risk is threefold.
Does a family history of lung cancer increase my risk?
Yes. If you have a family history of lung cancer, you are two to three times more likely to develop the disease. This has to do with shared environmental, behavioral, and genetic risks. However, if your parent smoked and got lung cancer, that doesn’t mean you will—if you don’t smoke. Smoking is still the biggest risk factor.
Lung Cancer and Single Cigarette:JAMA Internal Medicine. (2017). “Association of Long-term, Low-Intensity Smoking with All-Cause and Cause-Specific Mortality in the National Institutes of Health-AARP Diet and Health Study.” ncbi.nlm.nih.gov/pubmed/27918784
Lung Cancer and 39 Percent Lower Risk Quitting Smoking:Journal of the National Cancer Institute. (2018). “Lifetime Smoking History and Risk of Lung Cancer: Results From the Framingham Heart Study.” dx.doi.org/10.1093/jnci/djy041