Until the early 1900s, lung cancer was relatively rare. But as more people began to smoke, rates of lung cancer rose drastically.

Not every person who smokes will develop lung cancer, but smoking significantly increases your odds. People who smoke are 15 to 30 times more likely to get lung cancer than non-smokers. The longer you smoke and the more often you smoke, the higher your risk.

In this article we’ll take a closer look at the connection between smoking and lung cancer. We’ll also explain what the latest research has found about the health effects of e-cigarettes.

According to the World Health Organization (WHO), lung cancer is the most common cause of cancer death. It accounts for 1.76 million deaths around the world per year.

Here are some key facts about cancer and smoking.

When you breathe in tobacco smoke, thousands of chemicals enter your lungs. Many of these chemicals have the potential to damage the DNA in your lung cells.

Your body will work to repair the damage that’s done by these chemicals, but over time, smoking can cause more damage than your body can heal. Eventually this may lead to the formation of cancer cells.

Inhaling tobacco smoke can also damage the tiny air sacs called alveoli in your lungs. These microscopic air sacs are the center of your respiratory system’s gas exchange. They move oxygen into your blood, and expel carbon dioxide when you exhale.

Over time, the damage to the alveoli in your lungs can lead to chronic obstructive pulmonary disease.

Lung cancer can be divided into two primary categories:

About 80 to 85 percent of lung cancers are NSCLC, but SCLC cancers tend to be more aggressive.

Smoking increases your risk of both types of lung cancer, but at least 95 percent of people with SCLC have a history of smoking.

NSCLC can be divided into several subcategories depending on where the cancer cells start to grow.

  • Adenocarcinoma starts in the mucus cells that line your lungs. It’s the most common type of lung cancer in non-smokers, but it’s still more common in smokers than non-smokers.
  • Squamous cell carcinoma starts in the flat cells inside your airways. They’re less common than adenocarcinoma cancers but tend to be linked to smoking.

Over the past 25 years, an increasing number of measures have been taken in the United States to ban indoor smoking. Still, long-term exposure to secondhand smoke is attributed to about 7,000 lung cancer deaths in the United States each year.

A 2018 review of studies found that exposure to secondhand smoke significantly increases the risk of cancer for non-smokers, especially the risk of developing lung and breast cancer in women.

E-cigarettes are battery-operated devices designed to replicate the feeling of smoking by producing a mist and delivering nicotine. They’re still relatively new to the market, and there isn’t much research yet on the potential long-term health effects of e-cigarettes.

It’s not clear at this time if e-cigarette use increases your risk of developing lung cancer. According to the American Cancer Society, e-cigarettes still deliver some chemicals linked to cancer, although the amount is significantly lower than in traditional cigarettes.

When the liquid in the e-cigarette overheats, it can produce the cancer-causing chemical formaldehyde.

Researchers are still investigating other potential health consequences of e-cigarette use, but many experts highly discourage non-smokers, especially teenagers, from using e-cigarettes.

A chemical called diacetyl used in flavorings may increase your risk of developing a serious lung condition called bronchiolitis obliterans. Some e-cigarettes may also deliver heavy metals such as lead or tin.

Most e-cigarettes contain nicotine. Nicotine can hinder brain development in adolescents, and is highly addictive.

Along with lowering your risk of lung cancer, quitting smoking can improve many other aspects of your health. Some potential benefits of quitting tobacco include:

Roughly 10 to 15 percent of lung cancer patients have no history of smoking. Some factors, besides smoking, that may increase your risk of lung cancer include:

  • Exposure to radon. Radon is a naturally occurring gas that rises through the ground and through small cracks in the foundation of buildings. You can hire a professional or buy a radon testing kit to measure levels in your home.
  • Genetics. If an immediate family member had lung cancer (even if they didn’t smoke), you may be at an elevated risk for the disease.
  • Asbestos. According to the National Cancer Institute, exposure to asbestos can increase your risk of developing lung cancer, including a rare form called mesothelioma.
  • Other chemicals. According to the Centers for Disease Control and Prevention (CDC), exposure to certain chemicals such as arsenic, diesel exhaust, and some types of silica and chromium may also increase your risk of developing lung cancer. The risk may be even higher for people who also smoke.
  • Dietary factors. Researchers are still investigating the effect of diet on lung cancer. Research suggests that smokers who take a beta-carotene supplement may be at an increased risk of lung cancer.
  • Air pollution. According to the American Cancer Society, breathing polluted air may slightly raise your risk of lung cancer.

Smoking is the number one risk factor for lung cancer. Not every person who smokes will develop lung cancer, but smoking significantly increases your risk of this disease.

It’s never too late to quit. The longer you smoke, the higher your risk of lung cancer. When you stop, your body is able to undo a lot of the damage caused by the chemicals in tobacco smoke.