Radon causes about 20,000 cases of lung cancer each year, making it the leading cause of lung cancer in non-smokers in the U.S. This radioactive gas is released when uranium breaks down in soil, rocks and water. The gas then travels up the ground and into the air. The levels in outdoor air are typically safe but, when radon becomes trapped in houses or buildings, it can build up to dangerous levels.

But how does it cause lung cancer? Radon releases radioactive particles that can damage the cells that line your lungs, according to the National Cancer Institute. In turn, inhaling these particles for long periods of time may lead to cell mutations associated with lung cancer, per one 2013 review of research.

Radon cannot be seen, tasted or smelled, so it’s important to test your home. The Environmental Protection Agency estimates that almost one out of very 15 homes has high radon levels. Click here for more information on testing.

Working in some environments, such as shipyards, mines, textile plants and mills, may expose workers to asbestos — a type of fiber that is heat-resistant and often used for insulation — making them several times more likely to develop lung cancer. Older buildings may also contain asbestos, however, it is only dangerous if the materials containing it are damaged or disturbed such as from construction work.

Consistently inhaling or swallowing asbestos fibers can bind them to the mucus in your throat, windpipe or larger breathing tubes of the lungs, according to the American Cancer Society. If the fibers travel to small airways or the outer lining of the lungs and chest, they can wreak havoc on your cells, potentially leading to lung cancer.

If you work in any of these conditions mentioned above, talk to your employer and, if necessary, contact the Occupational Safety and Health Administration.

Note that your spouses can also be at risk. “It’s well documented that asbestos fibers can be on clothing and then get into the household, or someone can be exposed if they wash the clothes,” says Dr. Joseph Treat, professor of medical oncology at Fox Chase Cancer Center. If you are concerned, find a contractor who can test your home for asbestos.

Other harmful substances can be found in the workplace and have been linked to a higher risk of lung cancer, including:

• arsenic
• diesel exhaust
• some forms of silica
• chromium
• nickel
• beryllium
• cadmium
• tar and soot

The ACS recommends that if you work around these products to limit your exposure as much as possible.

Living in places with higher levels of air pollution, such as cities or near roads with a lot of traffic, may increase the risk of lung cancer. The International Agency for Research on Cancer estimates that 223,000 people worldwide died from lung cancer caused by air pollution in 2010.

Many different types of particles (solid or liquid and big or small) get thrown into the air we breathe. This includes things like acids, chemicals, metals, soil and dust, according to the American Lung Association. Our bodies are able to fight off bigger particles more easily — typically through a cough or a sneeze.

But those microscopic particles in the air are the most dangerous since they can wiggle their way deep into the lungs or even your blood, potentially resulting in cancer.

People who are infected with the human immunodeficiency virus (HIV) may have more than twice the risk of lung cancer than those who are not infected, according to the National Cancer Institute. However, it’s unclear if this is due to higher smoking rates in those living with HIV or the infection itself.

Some researchers theorize, based on emerging studies, that immunosuppression — or the weakening of the immune system due to infection — and inflammation may also play a role, but more studies need to be done to determine if this is the case.

Having a parent or sibling who’s had lung cancer means you may be twice as likely to develop lung cancer as those without any family history and your risk is even higher if your relative was diagnosed at a young age, according to the National Cancer Institute. However, it’s still unknown if the increased risk is because of shared genes or secondhand smoke exposure since cigarette smoking tends to run in families.

It is likely a mix of both genetic and shared environmental factors (such as indoor air pollution in a family home), according to a 2017 review of research published in Oncology Letters, but very few genes specifically linked to lung cancer have been identified.