Chemicals called carcinogens in cigarettes affect cellular DNA and can lead to the development of cancer. Quitting smoking can lower the risk of lung cancer, even if a person has already smoked for years.

Smoking cigarettes is the number one risk factor for lung cancer, which relates to around 80% to 90% of lung cancer deaths in the United States.

Aside from lung cancer, smoking has associations with an increased risk for at least 15 other types of cancer.

In this article, experts explain the science behind how smoking causes lung cancer and other health concerns and how quitting can lower a person’s risk.

“There are a number of chemicals in tobacco cigarette smoke that cause damage to healthy lung tissue,” explained Dr. Susan Scott, a thoracic medical oncologist at Johns Hopkins Medicine. “Exposure to these chemicals, called carcinogens, causes changes to cellular DNA that can lead to the emergence of cancer cells that grow uncontrolled, with the potential to form tumors and spread through the body.”

When carcinogens enter the cells in the lungs, they can alter a person’s DNA. Some of these changes affect the way cells grow. If the cells in the lungs lose control over these processes, it can lead to lung cancer.

“The 2020 Surgeon General’s report identified 70 carcinogens in tobacco smoke,” said Dr. James Davis, director of the smoking cessation program at the Duke Cancer Institute in North Carolina.

He noted that some of the most harmful of these include:

  • tobacco-specific nitrosamines
  • polycyclic aromatic hydrocarbons
  • aromatic amines
  • 1,3-butadiene
  • benzene
  • aldehydes, such as formaldehyde
  • ethyl oxide

The American Cancer Society also lists arsenic, ammonia, radioactive compounds, and carbon monoxide as potential cancer-causing chemicals in tobacco smoke.

“Some carcinogens, like cadmium and lead, come from the soil where tobacco is grown. Most carcinogens, however, come from burning tobacco,” Dr. Davis explained.

Similar chemicals are also found in other tobacco products, including cigars and smokeless tobacco.

“When a person inhales smoke, carcinogens enter the lungs and then enter the bloodstream, where they reach every organ in the body,” explained Dr. Davis. “The lungs get the highest dose of carcinogens, but every organ in the body is exposed.”

Aside from lung cancer, smoking has links to an increased risk for at least 15 other types of cancers, including:

  • cancers of the mouth, nose, throat, and esophagus
  • stomach cancer
  • kidney and liver cancers
  • pancreatic cancer
  • colon cancer
  • ovarian cancer
  • bladder cancer
  • cervical cancer
  • leukemia

Damage to the cells in the lungs can also cause other forms of lung disease, including chronic obstructive pulmonary disease (COPD), also known as emphysema, and asthma.

Additionally, chemicals in tobacco smoke can damage the blood vessels throughout the body, increasing the likelihood of a heart attack or stroke.

“Something many people do not know is that smoking is a major cause of type 2 diabetes,” added Dr. Davis. “In fact, people are 30% more likely to develop type 2 diabetes if they smoke.”

Many people worry that if they have smoked for many years, there is nothing they can do to prevent lung cancer. However, Dr. Davis explains that stopping can decrease their risk.

“The risk of lung cancer increases with the duration and intensity of exposure to cigarette smoking, so quitting can decrease that exposure for the time that a person is no longer smoking,” said Dr. Scott.

According to the American Cancer Society, the risk of lung cancer is cut in half after 10–15 years of quitting smoking. The risk for other types of cancer may decrease even more quickly, such as cancers of the:

  • mouth
  • throat
  • larynx, or voice box

However, people with a history of smoking may still develop lung cancer even after quitting, so screening is important.

“The reason lung cancer is so deadly is that at early stages, it causes no symptoms,” explained Dr. Davis. He noted that in many cases, people might not have any symptoms or realize they have cancer until it has already spread beyond the lungs.

This is known as metastatic disease. Doctors diagnose more than half of lung cancer cases at this stage, at which only 8.9% of people survive an additional 5 years.

“Screening enables us to diagnose lung cancer at earlier stages before a patient experiences any symptoms and when the cancer can still be potentially cured,” added Dr. Scott.

Annual lung cancer screening starting at age 50 is recommended for some adults with a history of smoking, even if they have quit within the last 15 years. Although screening cannot prevent lung cancer, it can help detect it earlier when there is an improved likelihood of survival.

“If you have ever smoked, be sure to talk with your primary care doctor about annual lung cancer screening to see if it is appropriate for you,” Dr. Scott recommended.

People interested in quitting smoking can talk with their primary care physician about resources to help, including counseling and medications, or call 1-800-QUIT-NOW (1-800-784-8669) for more support.

This section answers some frequently asked questions about smoking and cancer.

Is vaping worse than smoking?

“At this early point, the scientific community cannot say with any certainty whether vaping causes lung cancer,” said Dr. Davis. Lung cancer takes a while to develop, and because vaping products are relatively new, it can be hard to assess the level of lung cancer risk they may cause.

“In another 10–20 years, we may start to see people with lung cancer who vaped but never smoked. At that point, we will know if e-cigarettes cause lung cancer,” he said.

However, many carcinogens in cigarette smoke are also in vaping liquid at lower levels. Dr. Davis suggested that people who use vaping products may still be more likely to develop lung cancer than people who do not. However, the risk may not be as high as the risk associated with cigarette smoking.

Dr. Scott noted that while levels of some known carcinogens are lower in vaping products, there are other chemicals in them that researchers have not yet studied well. The potential health effects of these chemicals, including their effects on cancer risk, are still unknown.

Why do some smokers never get cancer?

“If we smoke, the carcinogens we inhale cause mutations in our DNA. This is fact, and it occurs in everyone who smokes,” emphasized Dr. Davis.

According to a 2016 study, a person who smokes a pack of cigarettes a day on average has approximately 150 mutations in the DNA of any given lung cell each year. “That’s about one mutation per cell every 2.5 days,” said Dr. Davis.

“With each mutation, there is a chance of getting lung cancer,” he explained. “Many mutations don’t lead to any problems at all. If, however, [a person] gets the wrong mutation, they can develop lung cancer.”

A 2020 study found that over 25% of cells in the airways of people who currently smoked had at least one mutation known to increase the likelihood of cancer. Additionally, up to 6% of cells had two or three known cancer-causing mutations.

“Smoking is like rolling dice over and over and hoping not to get snake eyes,” he said.

“The magnitude of risk increases with the duration and intensity of exposure to smoking, but it’s not a guarantee,” added Dr. Scott. “Sometimes there are additional exposures or risk factors, and some of it is chance.”

Other risk factors include:

  • workplace exposure to other carcinogens, such as asbestos, diesel exhaust fumes, or some forms of silica
  • a family history of lung cancer
  • prior radiation therapy
  • radon exposure
  • some dietary choices, such as eating a lot of red meat or drinking alcohol

Carcinogens in cigarette smoke can change the DNA in the cells of the lungs and other organs, increasing the likelihood of developing cancer. Smoking is the number one risk factor for lung cancer, and quitting can substantially decrease the likelihood of smoking-related health complications.

“Quitting smoking can be very challenging, and many people will need help,” said Dr. Scott. “There are many tools and resources to consider, including education, counseling, nicotine replacement, medications, and more.”