The Leading Causes of Lung Cancer

A young man sits in a window lighting a cigarette
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There are many probable and possible causes of lung cancer, but narrowing these down to the top 5 or 10 is sometimes helpful. Which causes are most important?

Causes Go Beyond Smoking

When we talk about the leading causes of lung cancer, our thoughts jump to smoking. But while some of the leading causes are obvious, others important causes may surprise you.

When we talk about the causes of lung cancer, we are primarily referring to risk factors for the disease.

There are many probably and possible risk factors for lung cancer. Yet sometimes narrowing these down to the top 5 or 10 can be most helpful. Why? In talking about risk factors we are talking about ways in which you might be able to reduce your risk. With some of these risk factors, such as smoking or testing your home for radon, you can expect a big return (with regards to risk reduction) from your efforts. With some of the possible or lesser causes, however, an investment of your time may have a lower return. Ideally, we would all be aware of all potential risk factors and change our lifestyles to avoid these causes. But in our rapidly moving society, that's not realistic.

What are the leading causes of lung cancer that everyone should know?


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, 10 percent of men and 20 percent 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, responsible for 27,000 lung cancer deaths each year. Radon exposure is the number one cause of lung cancer in non-smokers.

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.

Secondhand Smoke

The third leading cause of lung cancer, responsible for over 3,000 deaths each year in people who have never smoked, is secondhand smoke. Living with someone who smokes raises your risk of developing lung cancer by 20 percent to 30 percent, and even brief exposures can cause the damage that can lead to lung cancer.

Occupational Exposures

On-the-job exposure to cancer-causing substances is responsible for 6 percent to 17 percent of lung cancers in men in the United States. 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.

Air Pollution

Air pollution generated from traffic, the combustion of diesel fuel, coal, and wood is responsible for around 5 percent of lung cancer in men, and 3 percent in women in the United States. In some areas of the world, these numbers are significantly higher.

Other Causes and Possible Causes

There are many other possible causes of lung cancer that have been evaluated. If you are interested you may wish to check out the comprehensive list of risk factors for lung cancer. We know that there is a genetic component as well, especially when lung cancer is found in young people, women, and never smokers.

Bottom Line

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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