The Leading Causes of Lung Cancer

A young man sits in a window lighting a cigarette
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Looking at the leading causes of lung cancer is sometimes helpful. While there are many probable and possible causes, narrowing these down to the top 5 or 10 can make the big picture clearer. Even though many people equate lung cancer with smoking, tobacco use is only one culprit, and being aware of the other causes is important for smokers and never-smokers alike. After all, lung cancer in never-smokers is increasing in the United States.

What are the most important causes of lung cancer? We will begin with smoking because it's the leading cause, but spend time addressing this risk factor. After all, most people are aware of the link between smoking and lung cancer, but a much smaller number of people are aware of the other causes that may be preventable.


Smoking is responsible for 80 percent to 90 percent of lung cancers and causes roughly 160,000 cancer deaths each year in the United States. That said, at least 10% of men and 20% of women who develop lung cancer have never smoked, and over half of lung cancers related to smoking occur in former, not current, smokers.


Exposure to radon gas in our homes is the second-leading cause of lung cancer overall, and the leading cause in non-smokers. Radon exposure is thought to be responsible for 27,000 lung cancer deaths each year. To understand the extent of the problem, consider that 40,000 people die from breast cancer each year. Yet exposure to radon is completely preventable.

Radon gas results from the natural decay of uranium beneath our homes, and can enter our homes through cracks in the foundation, openings around drains, and gaps around pipes. Elevated levels of radon have been found in homes in all 50 states and throughout the world. Since radon is an invisible, odorless gas, the only way to know if you are at risk is to test your home for radon. Then learn if you can lower the levels in your home (it's almost always possible).

Occupational Exposures

On the job exposure to carcinogens (cancer-causing substances) is thought to be responsible for at least 6% to 17% of lung cancers in men in the United States (with some studies finding the risk as high as 27%). Some of the culprits include diesel fumes, organic solvents such as benzene, chemicals such as vinyl chloride, and metals such as chromium and arsenic.

Employers are required to provide information sheets about hazardous substances you may be exposed to, and it is important to check these out and take any recommended precautions. Keep in mind that wearing a mask may give you only false confidence, and sometimes specialized respirators are required to prevent the exposures that can lead to lung cancer.

Chemicals at Home

While we talk about occupational exposures, many of us have chemicals in our homes and garages that can likewise be toxic. Carefully read labels and use non-toxic products when possible. For example, it's possible to clean your home using many ingredients you cook with, such as vinegar, lemon juice, olive oil, and baking soda.

Air Pollution

Air pollution was named a carcinogen by the International Agency for Research on Cancer in 2013, and is now being recognized as a significant cause of lung cancer. Thought to be responsible for around 5% of lung cancers in men (and 3% in women), the estimates in other regions of the world are higher. For example, air pollution is thought to be responsible for 10% of lung cancers in the UK, even though pollution control there is much better than in many areas of the world.

It's actually air pollution (particulate matter in air pollution) that was named a carcinogen rather than any specific component. Particulate matter is generated from traffic, the combustion of diesel fuel, coal, and wood burning, and much more.

It's hard to avoid air pollution completely, but taking measures such as avoiding outdoor exercise when air quality is poor in your region may help.

Secondhand Smoke

Secondhand smoke is an important cause of lung cancer, but exposure to secondhand smoke is actually responsible for many more heart disease related deaths than lung cancer deaths. According to the Centers for Disease Control, it is responsible for 7,333 lung cancer-related deaths each year. Living with someone who smokes raises your risk of developing lung cancer by more than 20%, and even brief exposures can cause the damage that can lead to lung cancer.

Other Causes and Possible Causes

There are many other probably and possible causes of lung cancer. For example, we are learning that just like breast cancer, some people may have a genetic predisposition to developing the disease. Unfortunately, due to the stigma of lung cancer being a "smoker's disease," less research has been done looking for other causes compared to some other types of cancer.

A Word From Verywell

Lung cancer is a frightening disease. It is currently the leading cause of cancer-related deaths for both men and women in the United States and worldwide. At the same time, many cases of lung cancer could, in theory, be prevented. We don't know how to prevent lung cancer from ever occurring, but we do know of many ways in which you can reduce your risk. You have probably heard that smoking isn't a good idea, but fewer people are aware that doing a simple radon test (with a kit from the hardware store) and seeking out radon remediation if it is abnormal, could slash your risk for the second-leading cause overall and the leading cause of lung cancer in non-smokers.

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  2. Centers for Disease Control. Tobacco-Related Mortality. January 17, 2018.

  3. Roger Dobson. Exposure to spouse's smoking increases risk of lung cancer by over 20%. BMJ. 2004 Jan 10;328(7431):70. doi:10.1136/bmj.328.7431.70-c

  4. Centers for Disease Control. Health Effects of Secondhand Smoke. February 27, 2020.

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