Lung cancer causes and risk factors

This page was reviewed under our medical and editorial policy by

Maurie Markman, MD, President, Medicine & Science

This page was updated on September 14, 2022.

Each year, more than 234,000 people are diagnosed with lung cancer in the United States. No one knows if or when the disease will develop, but understanding the risk factors for lung cancer may help people take preventive measures to reduce the likelihood of developing the disease.

What causes lung cancer?

Smoking tobacco, the leading cause of lung cancer, is linked to up to 90 percent of lung cancer deaths in the United States. Other risk factors that may increase the risk of developing lung cancer include exposure to certain chemicals, gases or pollutants over time.

Lung cancer is caused when mutated cells in the lungs grow out of control, forming a tumor. In many cases, these altered cells die or are attacked by the immune system. But some cells escape the immune system and grow out of control, forming a tumor in the lung.

The lifetime risk of developing lung cancer for smokers and non-smokers combined
Download lung cancer infographic »

Lung cancer risk factors

Leading causes and known risk factors for lung cancer include:

Lung cancer and age

About two out of three lung cancers are diagnosed in people over age 65, and most people are older than 45. The average age at diagnosis is 71.

Is lung cancer hereditary?

Genetics may predispose certain people to lung cancer. Individuals with an immediate family member who has or had lung cancer (and who does not or did not smoke) may be more prone to developing the disease.

Exposure to tobacco smoke

Smoking is widely considered the leading cause of lung cancer. For those who don’t smoke but are exposed to smoke at home or work, secondhand smoke may significantly increase their risk of lung cancer. The National Cancer Institute (NCI) reports that tobacco smoking causes about nine in 10 cases of lung cancer in men and eight in 10 in women.  

Exposure to certain chemicals

Carcinogenic chemicals in the workplace, such as asbestos and other pollutants, may increase lung cancer risk, especially in people who smoke.

Can radon cause lung cancer?

Radon is a colorless, scent-less radioactive gas that is found in some houses and is a leading cause of lung cancer. 

Can air pollution cause lung cancer?

Exposure to air pollution may increase the risk of developing lung cancer, particularly for people who work or exercise outdoors in areas with high levels of pollutants in the air.

Ask us about the causes of lung cancer

Our virtual assistant is available 24 hours a day. We are here to provide information on various cancer types and information about City of Hope services.


Risk factors for lung cancer vary by type

Causes of non-small cell lung cancer

Genetic risk factors

Family history: A family history of lung cancer may increase the risk for developing non-small cell lung cancer (NSCLC). Some evidence points toward a genetic link in a few cases. However, researchers have not determined whether shared environmental or behavioral factors, such as radon gas or smoking, play a greater role in a family’s history of lung cancer than genetics.

Lifestyle risk factors

Tobacco use: Smoking tobacco (cigarettes, pipes or cigars) is linked to more than four out of five cases of all lung cancers. Heavy smokers and those who began smoking at a young age are at an increased risk of developing the disease. It is possible to significantly reduce the risk of lung cancer by no longer smoking. According to the U.S. Centers for Disease Control and Prevention, cigarette smokers are 15 to 30 times more likely to develop lung cancer than non-smokers, and smoking is linked to an estimated 80 percent to 90 percent of lung cancer deaths.

Secondhand smoke: Even people who don’t smoke may be at an increased risk for developing lung cancer if they're exposed to tobacco smoke.

Radon gas: A naturally occurring odorless gas, radon may be found in some houses or buildings. The U.S. Environmental Protection Agency considers exposure to radon gas as the number one cause of lung cancer in non-smokers. Kits are available to test for radon in the home or office.

Asbestos: Long-term exposure to asbestos is linked to an increased risk of lung cancer. Miners, mill workers or people who may have breathed in asbestos fibers are at a greater risk of developing lung cancer.

Industrial or workplace exposures: Inhaling chemicals or minerals, such as asbestos, arsenic, chromium, nickel, soot or tar may, over time, increase a person’s NSCLC risks. Workers in certain manufacturing or mining industries may have an increased exposure to these chemicals. Diesel exhaust and air pollution may also be harmful.

Previous treatments

A history of lung diseases, including previous lung cancers, may increase the risk for developing the disease. There is also a risk associated with other cancer treatments, like radiation therapy.

Causes of small cell lung cancer

Genetic risk factors

Family history: Anyone previously diagnosed with lung cancer or anyone with a family history of the disease has an increased risk. In particular, people who inherit chromosome 6 are more likely to develop lung cancer.

Lifestyle risk factors

Smoking: Cigarette smoke is a leading risk factor for small cell lung cancer (SCLC). The risk increases with the number of cigarettes smoked per day for any extended period of time. Smokers who quit before lung cancer develops may live longer than people who continue to smoke. This is because, once a smoker quits, the lungs are capable of repairing the damaged tissue.

Secondhand smoke: Non-smokers who are regularly exposed to secondhand cigarette smoke are also at an increased risk for developing SCLC.

Radon: When uranium breaks down in soil and rock, it releases a naturally occurring radioactive gas called radon. This gas may be found in the basements of older homes or buildings. Exposure to concentrated amounts of radon gas increases a person’s risk for developing SCLC. Test kits that can detect and measure levels of radon are widely available.

Workplace exposure: There are a variety of industries where workers are regularly exposed to carcinogens, such as asbestos, which increases their risk for lung cancer. Other workplace agents that increase the risk for SCLC include radioactive ores, inhaled chemicals or minerals, such as beryllium, cadmium, silica, vinyl chloride and nickel compounds, and diesel exhaust.

Previous treatments

A history of lung diseases, including previous lung cancers, may increase the risk for developing the disease. There is also a risk associated with other cancer treatments, like radiation therapy.

Causes of metastatic lung cancer 

Smoking: Smoking is the biggest risk factor for metastatic lung cancer, or cancer that spreads from the lung or lungs to other areas of the body. The amount and rate at which smokers use cigarettes may increase the chances of lung cancer, so people who smoke an excessive amount of cigarettes every day may have a higher risk of developing the disease than if they smoked occasionally. Because the symptoms often go unnoticed, the chance of the cancer spreading from the lungs to other areas of the body is also high. Lung cancer that spreads to other organs or tissue is considered metastatic lung cancer, despite where it has spread. For example, lung cancer that metastasizes to brain is still considered lung cancer, not brain cancer.

Lung cancer prevention

Knowing the risk factors for lung cancer is key to taking steps to help prevent the disease. Not smoking, avoiding secondhand smoke and understanding and avoiding exposure to environmental factors such as radon may help to reduce risk. According to the National Cancer Institute, studies have shown that smoking cigarettes that are low in tar or nicotine does not lower the risk. For people who do smoke, quitting—with the help of nicotine replacement products, counseling or other cessation efforts—may help reduce future risk.

Next topic: What are the symptoms of lung cancer?

Expert cancer care

is one call away.
appointments in as little as 24 hrs.