Causes and Risk Factors

The most significant cause of lung cancer is tobacco smoke. More than 8 million people in the United States have at least one serious illness caused by smoking, according to the American Lung Association. Approximately 80-85 percent of diagnosed lung cancers occur in former or current smokers. The more cigarettes you have smoked, the greater your chances of developing lung cancer.  However, we are now seeing increasing numbers of lung cancer cases among never-smokers.

Researchers believe that smoking marijuana can also increase your risk of developing lung cancer. It can irritate the throat and lungs, just as tobacco does. In addition, marijuana contains tar and volatile chemicals that may contribute to lung cancer risk.

Smoking—whether tobacco or marijuana—is not the only cause of lung cancer. Environmental exposure to materials like radon, asbestos, or uranium, or secondhand smoke also may cause lung cancer. In addition, genetic predispositions could play a role, although this has not yet been clearly established scientifically.

Risks for Current and Former smokers

We always encourage smokers to quit. Many people find smoking cessation therapy helpful. Quitting smoking lowers your risk of lung cancer, but you are, for many years, still at greater risk than someone who has never smoked.

Several factors can affect the lung cancer risk of former smokers. The longer you smoked, and the more cigarettes you smoked a day, the greater your risk of developing lung cancer. For this reason, current and former smokers who quit within the last 15 years, who are over the age of 55 years (under consideration to be lowered to 50) and have a history of smoking at least a pack a day for 30 years (under consideration to be lowered to 20) should talk with their physician about getting a low-dose computed tomography (CT) lung screening.

Risks for Never-smokers

Even if you have never smoked, consistent and regular exposure to secondhand smoke puts you at risk of lung cancer. But never-smokers with limited to no exposure to secondhand smoke can also develop lung cancer. The following factors can increase your risk: 

  • Lung scarring from certain types of pneumonia or other diseases
  • Exposure to radon, a colorless, odorless radioactive gas emitted by rocks and soil in some areas that can be trapped in houses and buildings
  • Extended exposure to carcinogenic materials such as:
    • Asbestos
    • Arsenic and some forms of silica and chromium
    • Coal dust, particularly in a factory or mining facility
    • Nuclear propulsion, herbicides, battlefield emissions, or other carcinogens, especially for veterans who served on submarines, in the Vietnam War, or in the Gulf War
    • Exposure to munitions. Munitions plant employees may be eligible for free screening under the Department of Energy’s Worker Health Protection Program

Risk factors for Both Smokers and Nonsmokers

Several other factors can increase your risk of lung cancer:

  • Family history: You might be at increased risk of lung cancer if a blood-related parent or sibling has had lung cancer. Your risk is higher if your relative was diagnosed before age 50.
  • Gender: More men than women are diagnosed with and die from lung cancer. However, we are seeing increasing numbers of younger females diagnosed with lung cancer.
  • Race: Diagnosis and mortality rates tend to be higher among non-white individuals. The reasons are unclear.


Education and prevention are important to reduce the number of people who develop lung cancer. Key to prevention is helping smokers quit through smoking cessation therapy. When you stop smoking, you may reverse smoking’s negative effects. Today’s smoking cessation therapy works so well you do not have to experience withdrawal and cravings in the process.