Although smoking is the #1 cause of lung cancer, almost one in five people in the U.S. diagnosed with lung cancer this year have never smoked. The second leading cause of lung cancer is exposure to radon in houses and buildings. Secondhand smoke and asbestos are also among the top causes. And in 2013, the World Health Organization (WHO) officially added outdoor air pollution, especially particulate matter, to the list.

The 2013 WHO report caused a stir when it was released. Though health care providers since the 1940s had suspected the role of air pollution in causing cancer, there was little scientific evidence other than research on diesel smoke particles. The WHO study combed thousands of scientific research papers before reaching its conclusion that air pollution, specifically PM2.5 fine particulates, are clearly a cause of lung cancer. The agency also concluded that air pollution is a cause of bladder cancer.

How air pollution causes cancer

Scientists are continuing to study the exact mechanism by which air pollution causes cancer. Soot particles and chemicals called polycyclic aromatic hydrocarbons (PAHs) are the prime suspects.

When PAHs are inhaled they can directly damage the DNA of cells in the lungs. In addition, fine and ultrafine pollution particles are easily inhaled and lodge deeply in the lungs, resulting in long-term inflammation and increasing cell-division rates. Scientists believe this effect can speed the spread of cells that have been damaged.

Other air pollutants and lung cancer

In addition to air pollution, there are many other airborne pollutants linked with an increased risk of developing lung cancer. These include:

• Tobacco Smoke.About 90% of all cases of lung cancer are associated with tobacco use, especially cigarette smoking. There are more than 7,000 chemicals in tobacco smoke and 69of them are known to cause cancer. The two primary carcinogens in tobacco smoke are nitrosamines and PAHs (see above).
• Radon.Radon is an invisible, odorless, radioactive gas that seeps into buildings from the ground through cracks in the floor, walls or foundation of a building. In addition to the link between radon to lung cancer, there is also evidence that suggests a link between radon exposure and leukemia.
• Asbestos.Asbestos is responsible for about 4% of all lung cancer deaths. Microscopic asbestos fibers that are inhaled become trapped in the lungs. Over time they cause inflammation and other health issues, and can eventually lead to the development of lung cancer.
• Airborne Chemicals.Exposure to a variety of airborne chemicals and gases can lead to lung cancer. While many chemicals are associated with various forms of cancer, exposure to formaldehyde and chromium (both present in tobacco smoke) have specifically been shown to be associated with lung cancer.

Protect yourself against pollutants

Although there are many other factors that contribute to lung cancer - such as genetics and family history - you can take action against environmental carcinogens. Here are a few recommendations:

1. Don't smoke.Tobacco smoking is the leading cause of lung cancer - by far. Don't smoke, stop smoking if you already do, and don't allow others to smoke indoors in your home.
2. Clean the air at home.A high-performance air purifier such as the IQAir HealthPro Plus will remove particles, chemicals and gases from the air you breathe at home or at work.
3. Take action against air pollution.Take steps to help reduce pollution. Drive less, consume less energy, reduce your consumption of wasteful products and packaging.
4. Test for radon.If you haven't already done so, have your home tested for radon. Do-it-yourself testing kits are available online or at hardware stores. Or, call a radon professional.

Leading a healthy lifestyle is another important way to help reduce your risk of cancer, including lung cancer. In addition to avoiding exposure to carcinogens, you should eat a diet filled with fruits and vegetables and engage in regular exercise. To learn more about cancer and how to reduce the risk of environmental exposure to carcinogens, visitwww.cancer.gov.