Lung cancer can happen to anyone, but the vast majority (about 90 percent) of lung cancer cases are due to smoking. Exposure to radon, a naturally existing radioactive gas, is the second leading cause of lung cancer.

Less commonly, lung cancer can also be a result of air pollution — the addition of harmful substances into the air. In 2013, the International Agency for Research on Cancer (IARC) of the World Health Organization (WHO) officially declared that outdoor air pollution is a Group 1 carcinogen.

Particulate matter, also known as particle pollution, was most closely associated with increased cancer risk. Particle pollution refers to a mix of tiny solid and liquid particles in the air we breathe.

In the United States, about 1 to 2 percent of lung cancer cases result from air pollution. Read on to learn about particle pollution and how it can increase your risk of developing lung cancer.

Over time, breathing in small particles released into the air can lead to cancer. Small particles can get trapped in the lungs. A buildup of these particles can cause damage to the cells of the lungs, leading to inflammation.

Inflammation over long periods of time can cause changes in how these cells replicate.

Research is ongoing, but a 2014 study suggests that long-term exposure to air pollution can cause damage to DNA, mutations, and altered gene expression. These changes may cause the cells of the lungs to grow uncontrollably.

Research has also shown air pollution to contribute to other health conditions, such as:

Air pollution is a complex mixture of particulate matter and gases produced by industrial and commercial activities, and different types of transportation like buses, trains, airplanes, and cars.

Many different types of air pollutants are linked to cancer. But according to the WHO, particulate matter is most closely associated with cancer. Particulate matter refers to a mix of tiny solid and liquid particles that are suspended in the air.

Particulate matter could be present in both indoor and outdoor air. These particles are typically very small, so you can’t see the individual particles. You can only see the haze that forms when millions of particles distort the sunlight.

Outdoor air pollutants

Examples of outdoor air pollutants include:

  • particles from wildfires
  • black carbon emitted from gas and diesel engines, coal power plants, and other sources that burn fossil fuels
  • nitrate particles from motor vehicle exhaust
  • sulfur dioxide emitted by large, coal-fired power plants
  • ozone (also called smog)
  • carbon monoxide from burning fuels

Indoor air pollutants

Indoor pollutants could arise from using open fires or traditional stoves for cooking, heating, lighting in the household, and other sources.

In developing countries, women and children in particular experience the highest exposure to air pollutants in their own homes, according to the WHO. This is because they spend the most time near the home’s cooking area.

Examples of indoor air pollutants include:

  • solid fuels, such as wood and charcoal, coal, or kerosene, for cooking
  • asbestos
  • radon
  • lead
  • carbon monoxide
  • tobacco smoke

Anyone who lives where particle pollution levels are high is at risk.

People living in low- and middle-income countries, as defined by the WHO, disproportionately shoulder the burden of outdoor air pollution, especially people living in Southeast Asia and Western Pacific regions. Many of these sources of air pollution are beyond the control of individuals.

The following factors increase your likelihood of developing lung cancer from air pollution:

  • living in a city, especially near heavily trafficked roads
  • frequent exposure to dust and fumes at work
  • exposure to asbestos at work
  • smoking
  • breathing in second-hand smoke
  • a family history of lung cancer
  • a personal history of lung cancer
  • previous radiation therapy to the chest

In addition, a new report from the American Lung Association found that People of Color were 61 percent more likely to live in a U.S. county with unhealthy air than white people.

Keep in mind that lung cancer cases may be attributed to more than one risk factor at the same time.

Research suggests that exposure to air pollution can increase lung cancer mortality for people who already have lung cancer.

For example, one large population-based study of over 350,000 people who received a diagnosis of lung cancer found lower survival rates linked with higher average exposure to air pollution.

There are steps you can take to protect yourself from indoor air pollution:

  • Reduce your exposure to secondhand smoke from cigarettes. Smokers should go outside to smoke, well away from windows.
  • Avoid burning wood and coal to heat your home and cook.
  • Test your home for radon levels. If radon levels are high, contact a licensed professional to install a radon reduction system.

It’s not always possible to protect yourself from outdoor air pollution, but here are a few things you can try:

  • Avoid or limit your time outdoors on days when air quality is poor. The Environmental Protection Agency (EPA) uses an air quality index (AQI) to determine when air quality in a particular area is considered unhealthy or hazardous. Air quality forecasts and real-time air quality data can be found on the EPA’s AirNow Website.
  • Plan your walk, run, or bike ride for times when traffic is less busy and use routes that avoid busier roads.
  • When driving on busy roads, keep the car’s ventilation setting to “recirculate.”
  • Avoid burning wood or trash in your yard.
  • Avoid idling vehicles, especially with diesel engines.
  • Live in areas with low levels of air pollution. Of course, this isn’t always realistic.

Clean air is a human right.

To reduce outdoor air pollution, industries will need to invest in clean technologies to reduce smokestack emissions and improve waste management. Cities will need to invest in rapid urban transit, and walking and cycling networks that help reduce the number of cars on the road, among other measures.

Investments in renewable power sources like solar, wind, or hydropower can also help lower air pollution. You can do your part by calling members of Congress or your local government to protect our health from air pollution.

Lung cancer is the top cause of cancer death in the United States. While there’s an established and concerning link between air pollution and lung cancer, active smoking is still responsible for most lung cancer cases.

Exposure to particulate matter accounts for just a small percentage of lung cancer cases. Some people are at a higher risk, especially people who live in areas with higher levels of air pollution.