About 21,000 people die from lung cancer each year in the United States. Smoking is the No. 1 risk factor for lung cancer, but about 1 out of 7 lung cancer deaths occur in people who have never smoked. Radon may be responsible for some of these deaths.

Exposure to radon is the second leading cause of lung cancer. It causes the most lung cancer cases in people who don’t smoke (and are not exposed to second-hand smoke). Like tobacco smoke, radon damages the cells of your lungs. The more you are exposed to radon, the higher your chances are of developing lung cancer. About 12 percent of lung cancer cases in the U.S. are caused by radon.

What Is Radon?

Radon is a radioactive gas. You can’t see, smell, or taste it. Radon is released into water and into the air when uranium and other radioactive substances in rocks or dirt break down. Radon is classified as a carcinogen — a chemical that has the potential to cause cancer.

Radon is found both outdoors and indoors. Outside, it is usually found at very low levels that won’t put you at risk for cancer. Generally, the radon level found in the outside air is 0.4 picocuries per liter, or pCi/L. Indoor radon levels are usually higher — those occur at an average level of 1.3 pCi/L.

Radon can be found in homes, offices, and schools. Because this gas comes from the ground, levels of radon in homes tend to be highest in the basement or ground floor. A building’s radon levels are affected by things like the materials it is made with and how ventilated it is. Additionally, certain geographic areas naturally have higher radon levels than others.

How Does Radon Affect the Lungs?

Radon gas can enter the lungs as you breathe in. The gas molecules can enter deep into your lung tissue. Because radon is radioactive, the molecules give off particles that damage DNA in your surrounding lung cells, leading to gene mutations that could cause cancer.

Radon and Lung Cancer Risk

Radon’s connection with lung cancer was first discovered when doctors noticed that underground miners who processed uranium had high rates of lung cancer.

Several studies in multiple countries have analyzed radon and its association with lung cancer. In one recent analysis that combined many such studies, researchers found that the higher the radon levels in your environment, the more likely you are to develop lung cancer.

Research also shows that radon can work together with cigarette smoke to cause lung cancer. Being exposed to both substances further increases your risk compared to if you are exposed to just one of them:

• About 26 percent of people who smoke who are exposed to high levels of radon (20 pCi/L) develop lung cancer.
• About 3.6 percent of people who don't smoke who are exposed to high levels of radon are diagnosed with lung cancer.
• About 2 percent of people who smoke who are exposed to low levels of radon (1.3 pCi/L) develop lung cancer.
• About 0.2 percent of people who don't smoke who are exposed to low levels of radon are diagnosed with lung cancer.

Some studies have found that radon can increase the chances of developing all types of lung cancer equally. Others have found that radon exposure may be more likely to lead to small cell lung cancer.

Reducing Risk of Lung Cancer From Radon

In the U.S., 1 out of 15 homes has increased levels of radon. Testing your home for radon can help you determine how much of the gas you are being exposed to. If tests show that radon levels are high, you can get your home fixed to keep radon out.

Radon Testing

You can buy do-it-yourself radon test kits at home improvement stores or online. Follow the instructions on the package to determine radon levels in your home. Often, the tests involve opening the package, leaving the device sitting out for the recommended number of days, and mailing it to a lab to be tested.

Another option is to hire a testing company that will come to your home and measure radon levels. Make sure that the company you hire is staffed by people who have been professionally certified.

You can also contact your state radon program. They can offer more information about how to test your home for radon or give you a list of qualified radon testers in your area. Some state radon programs may also provide free or discounted do-it-yourself radon test kits.

Fixing Radon Levels

Most homes have some radon, so testing will probably detect low radon levels. You should make repairs to your home if you find that indoor radon concentrations have reached 4 pCi/L or higher, according to experts like the U.S. Environmental Protection Agency (EPA) and the U.S. Surgeon General. If testing shows that your house has more than 4 pCi/L of radon gas, perform a second test to make sure you have accurate results.

High levels of radon can be fixed with a radon reduction system or a radon mitigation system. These systems can be installed in your home by an accredited radon service provider. Radon reduction systems may involve solutions like creating more ventilation under the floors or sealing cracks or gaps in walls and floors to prevent radon from leaking in.

Lung Cancer Screening

Screening tests can help detect lung cancer at an early stage. For people who are at increased risk of lung cancer, regular screening can help reduce cancer deaths.

Public health experts recommend that people with a history of smoking start undergoing yearly lung cancer screening starting at age 50. If you have been exposed to high levels of radon, you, too, may want to ask your health care provider about whether regular doctor’s visits and screening tests may be a good idea.

The combination of radon and smoking does even more damage than each substance alone. With that in mind, cancer screening is especially important if you smoke or who have lived or worked in buildings with a lot of radon.

Talk With Others Who Understand

On MyLungCancerTeam, the social network for people with lung cancer and their loved ones, more than 4,700 members come together to ask questions, give advice, and share their stories with others who understand life with lung cancer.

Have you tested radon levels in your home? Share your experience in the comments below, or start a conversation by posting on your Activities page.