What causes lung cancer?

Smoking tobacco and exposure to certain chemicals can greatly increase your risk of getting lung cancer. Nearly 90 percent of all lung cancers are due to cigarette smoking, according to the Centers for Disease Control and Prevention (CDC).

Lung cancer is caused by a mutation in your DNA. When cells reproduce, they divide and replicate, forming identical cells. In this way, your body is constantly renewing itself. Inhaling harmful, cancer-causing substances, or carcinogens, damages the cells that line your lungs. Examples of these carcinogens include:

  • cigarette smoke
  • asbestos
  • radon

At first, your body may be able to repair itself. With repeated exposure, your cells become increasingly damaged. Over time, the cells begin to act abnormally and grow uncontrollably. This is how cancer can develop.

Several precancerous changes have to occur before cancer actually manifests. The buildup of extra cells causes tumors, which are either benign or malignant. Malignant cancerous lung tumors can be life-threatening. They can spread and even return after they have been removed.

Read on to learn about the personal and environmental factors that can cause lung cancer.


Current research suggests that if a member of your immediate family has had lung cancer, you may have a slightly higher risk of developing the disease. Immediate family includes the following relations:

  • mother
  • father
  • sibling
  • aunt
  • uncle
  • grandparent

This elevated risk is true even if you don’t smoke. It’s unclear whether genetics causes lung cancer or merely increase your susceptibility to it.


According to the American Cancer Society, lung cancer mostly occurs in older adults. Two out of three people diagnosed with lung cancer are 65 or older. The average age at the time of diagnosis is about 70. The older you are, the longer you have been exposed to harmful chemicals. This longer exposure increases your risk for cancer.

Past lung diseases

Past lung diseases can cause inflammation and scarring in the lungs. Examples of these diseases include tuberculosis, chronic obstructive pulmonary disease (COPD), chronic bronchitis, and emphysema. You may be at a greater risk of developing lung cancer if you have a history of chronic diseases that affect the lungs.

Radiation therapy to the chest

Radiation therapy used to treat other cancers like non-Hodgkin’s lymphoma and breast cancer may increase your risk of lung cancer. This risk is higher if you smoke.

Secondhand smoke

Even if you don’t smoke, being exposed to secondhand smoke can increase your risk of lung cancer. This exposure can occur at any place you spend time, such as:

  • home
  • work
  • restaurants
  • bars

According to the CDC, each year about 3,000 people in the United States who have never smoked die from lung cancer due to secondhand smoke.


Smoking tobacco is the number one risk factor for lung cancer, accounting for nearly 90 percent of all cases, according to the CDC. Tobacco and tobacco smoke contain more than 7,000 chemicals, many of which are carcinogenic. Examples of carcinogenic chemicals contained in tobacco smoke are nitrogen oxide and carbon monoxide. Inhaling the chemicals in a cigarette immediately triggers a change in lung tissue. Initially, your body may be able to repair the damage, but its ability to repair decreases as exposure continues. The more frequent and the longer you smoke, the greater your chance for lung cancer.


A balanced diet provides your body with the vitamins and minerals it needs to maintain good health. If you don’t eat a diverse mix of healthy foods, including fruits and vegetables, you may have an increased risk for lung cancer. This is especially true if you smoke tobacco.


Radon is a gas that occurs naturally with the breakdown of uranium in rocks and soil. It’s odorless, colorless, and tasteless.

This gas can seep into building foundations and into living and working spaces. Radon is difficult to detect and you could be exposed without knowing it. People who smoke have an increased risk from the effects of radon than those who don’t smoke. Radon is the second-leading cause of lung cancer in the United States, according to the CDC.


Asbestos is an industrial material used in construction for insulation and as a fire retardant. When the material is disturbed, small fibers become airborne and can be inhaled. You’re at a greater risk for developing lung cancer if you’re exposed to asbestos on a regular basis.

Other chemicals

Other chemical exposures can raise your risk of lung cancer. Some examples are:

  • arsenic
  • beryllium
  • cadmium
  • vinyl chloride
  • nickel compounds
  • chromium compounds
  • coal products
  • mustard gas
  • chloromethyl ethers
  • diesel exhaust

Learn how to reduce your risk of lung cancer »