What Causes Lung Cancer?

Medical research is advancing constantly. We now know some core risk factors increase a person’s risk of a lung cancer diagnosis.

The primary risk factor associated with a lung cancer diagnosis is smoking. In fact, nearly 90% of all lung cancer cases¹ are in some way related to smoking cigarettes or other tobacco products. This can be through personal smoking or secondhand smoke.

That said, smoking isn’t the only risk factor associated with this disease. Exposure to toxic substances, a family history of lung cancer, and genetics also play a role.

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Risk factors for lung cancer

According to the American Cancer Society (ACS), lung cancers remain the leading cause of cancer deaths for both men and women.

In the United States, Northern Europe, and Western Europe, the prevalence of lung cancer has been decreasing in men. In Eastern and Southern European countries, the incidence of lung cancer has been rapidly increasing. 

There is a range of factors that increase an individual’s chance of getting lung cancer. Some factors, like smoking and exposure to carcinogenic substances, are environmentally and behaviorally controllable. Others, like age, sex, and genetics, are not. 

Environmental or external risk factors include smoking, secondhand smoking, radiation, radon, asbestos, and other carcinogens. 


Smoking cigarettes, or any tobacco-based product, including pipes and cigars, is the biggest external risk factor leading to lung cancer cases. Tobacco smoke contains at least 70 known² carcinogens.

Statistically, smokers are 15-30 times more likely³ to get lung cancer than non-smokers. Even infrequent smoking, or only a few cigarettes a day, will increase a person’s risk.

The best prevention is never to smoke at all. However, long-term smokers will reduce their risk by cutting down or quitting entirely. Quitting tobacco at any age reduces lung cancer risk. 

Gradually, as education around the dangers of smoking increases, the number of lung cancer cases is showing signs of decline⁴ with approximately 2.2% to 2.3% lower incidence per year—twice as fast in men as in women. This may be due to different smoking behaviors in the sexes.

What about secondhand smoke? 

Even when a person is not actively smoking cigarettes or tobacco products, there may still be damage to their lungs caused by inhaling secondhand smoke. 

Secondhand smoke also contains over 7000 chemicals, and even non-smokers are vulnerable to these carcinogens. There is no way to be around secondhand smoke without some level of risk. The Centers for Disease Control and Prevention (CDC reports that 2.5 million⁵ non-smoking adults have died due to secondhand smoking since the 1964 Surgeon General’s Report.

Radiation therapy 

Some radiation-based therapies used to treat cancers may also increase a patient’s risk for lung cancer. We also know about radiation exposure in workers in various jobs and survivors of Hiroshima.

Radiation therapies damage healthy cells. Research suggests that there is some risk of developing second cancers⁶ as a result of radiation-based cancer treatments. 


Radon is a naturally occurring radioactive gas and a decay product for uranium, found in rock, soil, and groundwater. Radon in indoor air is estimated to cause 21,000 lung cancer⁷ deaths every year.

After smoking, radon exposure is the second largest risk factor for lung cancer, the number one cause of lung cancer among non-smokers. 

The best way to prevent radon exposure is to ensure that all homes, public spaces, and workplaces are tested regularly. 


Asbestos is a naturally occurring fibrous silicate mineral used since ancient times. In modern times it is a highly toxic industrial building material that was used widely during the 1970s due to its fire retardancy and insulating properties. 

Asbestos became a primary building material for many essential U.S industries, including automotive, construction, manufacturing, and the military.

Asbestos has been proven to be a highly dangerous substance with very harmful side effects in recent years. When asbestos is disturbed, it releases small fibers into the air. When inhaled, these fibers increase a person’s risk of developing lung cancer. 

As well as asbestos, there are a number of other chemicals and substances that have been used in workplaces and construction that you should avoid. 

These include:

  • Arsenic

  • Diesel exhaust

  • Cadmium

  • Chloromethyl ethers

  • Beryllium 

  • Vinyl chloride

  • Nickel compounds

  • Mustard gas

  • Chromium compounds

  • Coal products

  • Mustard gas

We can avoid all the risk factors discussed above in the environment or our behavior to limit lung cancer risk. 

However, the following group of risk factors is slightly different. 

As well as external substances and environmental factors, lung cancer has also been linked to causes including human genetics, sex, race, and age. We cannot change these things about ourselves, but identifying whether we are at increased risk is often the key to achieving an early diagnosis. 


A family history of lung cancer may increase an individual’s risk⁸ of developing it themselves. 

For example, any person with a mother, father, sibling, aunt, uncle, or grandparent who had lung cancer at some point during their lifetime will be at increased risk. 

Inherited gene changes are DNA mutations passed from a parent to their child. These inherited gene changes can increase a person’s risk of developing cancer. Researchers have observed that some individuals inherit an inability to break down cancer-causing chemicals (e.g., those in cigarettes). 

Acquired gene changes are those acquired during a person’s lifetime. These gene changes are not inherited. Instead, they are brought on by exposure to environmental or factors like smoking or chemical exposure. 

It’s important to note that the family’s linked disease risk may be related to a shared environment. 

There are social and lifestyle factors that also influence the prevalence of lung cancer within a family unit. For example, if parents smoke, it may be more likely that their children also smoke or that their children inhale a significant amount of secondhand smoke. 


A person’s age also impacts their level of risk for developing lung cancer. As a general rule, lung cancer is much more prevalent in older generations. 

This is reflected in the fact that the average age of diagnosis⁹ is around 70. Very few people under the age of 45 will be diagnosed with lung cancer. 

Past lung diseases

Some studies have suggested a link between chronic disease and cancer risk. 

A 2018 study¹⁰ into cancer risk associated with chronic diseases found that they may “contribute to more than one-fifth of the risk for incident cancer.” 

The risk of lung cancer may be higher for those with a history of chronic diseases to the lungs, such as tuberculosis, COPD, chronic bronchitis, and emphysema. 

The lowdown

Many risk factors contribute to a patient’s lung cancer diagnosis. Research is ongoing, and scientists are identifying new causes and treatment options every day. 

While there is no one way to prevent lung cancer completely, education goes a long way. So does minimizing the number of external risk factors—like smoking and exposure to harmful substances. 

Learn about the changes you can make today to help reduce your chances of developing lung cancer. 

  1. What Are the Risk Factors for Lung Cancer? | Centers for Disease Control and Prevention (CDC)

  2. Harmful chemicals in tobacco products | American Cancer Society

  3. What Are the Risk Factors for Lung Cancer? | Centers for Disease Control and Prevention (CDC)

  4. Decline in Cancer Death Rate Largely Driven by Decreasing Lung Cancer Mortality | Cancer Therapy Advisor

  5. Health Effects of Secondhand Smoke | Centers for Disease Control and Prevention (CDC)

  6. Second Cancers Related to Treatment | American Cancer Society

  7. What are the health effects from exposure to radon? | United States Environmental Protection Agency (EPA)

  8. What Are the Risk Factors for Lung Cancer? | Centers for Disease Control and Prevention (CDC)

  9. Key Statistics for Lung Cancer | American Cancer Society

  10. Cancer risk associated with chronic diseases and disease markers: prospective cohort study (2018)

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We make it easy for you to participate in a clinical trial for Lung cancer, and get access to the latest treatments not yet widely available - and be a part of finding a cure.

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