Research suggests that a combination of toxin exposure, genetics, and hormones may play a role.

Tobacco smoking continues to account for most lung cancer cases and related deaths. Although smoking rates are decreasing worldwide, lung cancer rates are increasing, particularly among people who do not smoke.

Female nonsmokers account for about two-thirds of lung cancers in people who do not smoke.

In 2022, lung cancer was the second most common cancer and the second most common cause of death from cancer among the global female population.

An estimated 50% to 60% of lung cancers in people who have never smoked are adenocarcinomas, followed by squamous cell carcinomas (10% to 20%) and small cell lung cancers (6% to 8%).

This may be due to a combination of factors — including exposure to toxins, genetics, and sex hormones — rather than a single risk factor like tobacco use.

Whether you’re exposed to secondhand smoke at home or at work, the carcinogens can increase your risk of developing lung cancer, as well as heart disease and stroke.

There’s no “safe” level of secondhand smoke exposure — even short-term exposure is considered unsafe.

Secondhand smoke contains a variety of toxins, including:

  • arsenic ammonia
  • benzene
  • formaldehyde
  • hydrogen cyanide
  • vinyl chloride

The risk of secondhand smoke-related lung cancers appears to be greatest in people who have a spouse or partner who smokes.

In the United States, more than 19,000 deaths are attributed to secondhand tobacco smoke each year. Nonsmokers account for more than 7,300 lung cancer deaths.

Exposure to other toxins may also increase the risk of lung cancer in nonsmokers. This includes:

The sex hormone estrogen may also contribute to lung cancer development.

Many lung tumors have receptors that allow estrogen to “feed” cancer cells, helping them grow and spread. What’s surprising is that some lung tumors can even produce their own estrogen, creating a self-sustaining cycle.

This may help explain why lung cancer differs between sexes. People who are premenopausal may be at a higher risk of more aggressive lung cancers than people who are postmenopausal.

Researchers are now investigating whether treatments that block estrogen — already widely used in breast cancer — could help improve survival rates for female nonsmokers.

Lung cancer in nonsmokers may also have a genetic component. The genetic mutations (changes) that could contribute to it are mostly the type you can acquire during your lifetime, not the type you might inherit.

Acquired gene mutations that are involved in nonsmoking lung cancer development are called driver mutations. Examples include:

Genetic mutations are usually not detected until after a lung cancer diagnosis. But genetic testing is still important in these cases because it can influence a doctor’s decisions about treatment. If driver mutations are present, certain targeted therapies can be most effective.

Driver mutations can also develop in people who have a history of smoking, but this is less common.

Nonsmoking adults with a history of lung disease may also be at an increased risk of developing lung cancer.

This includes chronic obstructive pulmonary disease (COPD) and asthma, both of which are more common and more severe among the female population.

A 2020 review suggests that pulmonary fibrosis (scarring of your lungs) may also contribute to future lung cancer development.

While current research has not yet found a direct cause-and-effect relationship, some experts are looking into the role that certain viruses might play in later lung cancer development in nonsmokers.

This includes:

Currently, the U.S. Preventive Services Task Force (USPSTF) recommends annual lung cancer screenings via a CT scan for adults who meet all the following criteria:

  • They are 50 to 80 years old.
  • They currently smoke or have stopped within the last 15 years.
  • They have a 20-pack-year smoking history (which means they’ve smoked 1 pack of cigarettes per day for 20 years or 2 packs per day for 10 years).

The problem is that these guidelines do not account for nonsmokers who might have other risk factors, such as a history of secondhand smoke exposure.

Furthermore, nonsmokers who develop lung cancer tend to do so at a younger age than those who have a history of smoking.

The USPSTF does not recommend annual screenings for nonsmokers because the risk of radiation exposure from regular CT scans could possibly outweigh the benefits.

But if you wait to get screened until you have symptoms of lung cancer, the cancer may have already become advanced or spread. This can be a challenging situation to navigate.

Instead, a doctor may recommend regular screenings based on other individual risk factors. If you think you may need screenings, talk with a doctor. They can help you figure out your next steps.

Lung cancer symptoms

Contact a doctor right away if you’re experiencing the following possible symptoms of lung cancer:

  • chest pain
  • chronic fatigue
  • coughing up blood
  • persistent or worsening cough
  • recurring pneumonia
  • shortness of breath
  • unintentional weight loss
  • wheezing

While smoking rates are decreasing, lung cancer cases are increasing among nonsmoking females. Researchers believe this could be due to toxin exposures in work and home environments, as well as genetics, hormones, and other risk factors.

Because there are currently no screening guidelines for nonsmokers, lung cancer can be difficult to detect in its early stages.

Consider talking with a healthcare professional if you develop respiratory symptoms that concern you or if you have risk factors for lung cancer.