What Are the Causes of Lung Cancer?

Lung cancer involves the out-of-control growth of abnormal cells in the lining of the bronchi (tubes that move air in and out of the lungs) and other parts of the lungs. (1)

Researchers have identified harmful substances (carcinogens) that can cause cell damage and lead to lung cancer. Genes may also play a role.

Knowing the causes of lung cancer can help you take appropriate steps to minimize risk factors and recognize symptoms.

Lung Cancer Causes in Smokers vs. Nonsmokers

Smoking is the No. 1 risk factor for lung cancer, contributing to 80 percent of lung cancer deaths in women and 90 percent of lung cancer deaths in men. (2) Cigar and pipe smoking are almost as likely to cause cancer as cigarette smoking. (3)

While tobacco smoke is the top cause of lung cancer, not everyone who smokes will develop the disease.

Secondhand smoke, or smoke that’s breathed in from someone else’s cigarette, cigar, or pipe, can also lead to lung cancer.

Secondhand smoke causes more than 7,300 deaths among nonsmokers in the United States every year. (4)

RELATED: The Best and Worst Ways to Quit Smoking

Radon

Exposure to radon, a natural, invisible gas that can get trapped in buildings, is the second leading cause of lung cancer.

The U.S. Environmental Protection Agency (EPA) estimates that about 10 percent of all lung cancer cases are caused by radon, leading to about 21,000 lung cancer deaths each year.

The agency also estimates that nearly 1 out of every 15 homes in the United States has dangerous levels of radon.

You can test your home with a simple, inexpensive kit to see if radon levels are too high. (5,11)

Asbestos

Asbestos is a material used for insulation in construction. When fibers of asbestos break off, they can become airborne and dangerous to inhale, causing scarring and inflammation in the lungs as they accumulate.

Exposure to asbestos raises your risk of lung cancer as well as mesothelioma, a rare type of cancer that starts in the pleura — the lining surrounding the lungs.

Many studies have shown that the combination of smoking and asbestos exposure is particularly hazardous.

While asbestos was once commonplace, many countries, including the United States, have greatly reduced its use. (6)

Air Pollution

Particle pollution (a mix of tiny solid and liquid particles in the air) can cause lung cancer.

Between 1 percent and 2 percent of lung cancer cases are caused by outdoor air pollution. Common culprits for air pollution include diesel truck exhaust, coal-fired power plants, and wood smoke. (7)

Other Causes

Other potential causes of lung cancer include:

• Radiation Therapy to the Chest Radiation to the chest area as a treatment for certain cancers may cause lung cancer.
• Other Chemicals Exposure to several other substances has been linked to the development of lung cancer. Some of these include arsenic (in drinking water), chromium, and some forms of silica. (8)

RELATED: What Is Lung Cancer?

Marijuana

There’s no evidence that smoking marijuana raises lung cancer risk, but there’s reason to believe it may. Marijuana smoke contains tar and several other cancer-causing substances that are found in tobacco smoke.

Since marijuana is illegal in many places in the United States, researchers face challenges in studying its health effects.

And since studies of lung cancer and marijuana have often found that many marijuana smokers also smoke cigarettes, it’s hard to know how much each contributes to lung cancer risk. (3)

A Swedish study that followed nearly 50,000 men over a 40-year period found a link between marijuana use and lung cancer. Heavy marijuana smokers — those who reported smoking more than 50 times in their life — were twice as likely to get lung cancer as those who didn’t smoke marijuana. (9)

Inherited Gene Changes

Some people inherit certain gene mutations — or changes in their DNA — that can raise their risk of developing cancer.

These gene changes alone don’t cause many cases of lung cancer, but they do play a role in some. For instance, individuals who inherit certain mutations on chromosome 6 are more likely to develop lung cancer, even if they don’t smoke.

Additionally, some people inherit defective DNA repair enzymes that make them more sensitive to chemicals that cause cancer.

Doctors are working on developing specific tests that can identify people who have these gene defects. (3)

Acquired Gene Changes

More often, gene mutations that impact lung cancer are “acquired,” rather than inherited. This means that the defect develops during your lifetime.

These acquired mutations often occur because of exposure to cancer-causing substances, such as tobacco smoke.

But some gene changes happen without a known cause and may just be random events.

Everyone develops mutations in cells during the course of their lives, but toxic exposures cause more of those mutations, increasing the risk of acquiring a mutation that lead to cancer.

Gene mutations may also make some lung cancers more aggressive. (3)

RELATED: What You Need to Know About Testing for Tumor Mutations in Metastatic Non-Small-Cell Lung Cancer

Causes in Men vs. Women

Historically, rates of lung cancer have always been higher in men than women. But a study from 2018 found that rates of lung cancer are now higher in women than men among white and Hispanic people born since 1965.

For instance, rates of lung cancer among white women ages 40 to 44 went from 12 percent lower than men during the 1995–1999 period to 17 percent higher during the 2010–2014 period.

More studies are needed to understand the cause, but the researchers speculate that women may be more susceptible to the health hazards of smoking than men, or are more likely than men to get lung cancer even after quitting. (10)