Risk Factors

Tobacco smoke

Tobacco smoke causes most cases of lung cancer. It is by far the most important risk factor for lung cancer. Among those newly diagnosed, it is estimated that about 80%-90% are either current or former smokers; the remaining 10%-20% are never smokers.¹

Harmful substances in smoke damage lung cells, cause mutations, and make the lungs more vulnerable to other cancer-causing environmental factors, such as asbestosA group of minerals that take the form of tiny fibers; has been used as insulation against heat and fire in buildings and radonA radioactive gas that is released by uranium, a substance found in soil and rock. Smoking cigarettes, pipes, or cigars can cause (or accelerate) lung cancer. If you are at increased risk of developing lung cancer because of smoking, speak with your doctor, who may be able to give you additional information, including referring you to a screening program. Read more about screening here.¹

Secondhand smoke—smoke from other people’s tobacco use—can even cause lung cancer in nonsmokers. The more and the longer a person is exposed to smoke, the greater the risk of lung cancer. It is best not to start smoking. However, even those who do smoke can significantly lower—although never eliminate even after many years of non-smoking—their risk of developing lung cancer by quitting. In addition, it is never too late to quit; there are health benefits, including longer survival and a lower likelihood of a recurrence of their lung cancer, even to those who don’t quit smoking until after a lung cancer diagnosis. There are many tobacco cessation programs to help a smoker quit; two such programs are the US government’s program at www.smokefree.gov and the American Lung Association’s Freedom from Smoking® Online program.^1,2,3

Radon

Radon is a radioactiveGiving off radiation gas that you cannot see, smell, or taste. It forms naturally in soil and rocks. Radon damages lung cells, and people exposed to radon are at increased risk of lung cancer. Radon is the second leading cause of lung cancer, and the risk of lung cancer from radon is even higher for smokers. Radon can be present in buildings. Because there is no way to know for sure without testing whether radon is present, the US Environmental Protection Agency (EPA) recommends that people test their homes for radon levels. If a high level is found, there are ways to lower it to make a home safer. For information and resources on how to protect yourself from exposure to radon, read the Environmental Protection Agency's Citizen's Guide to Radon or contact your local Department of Health.^1,4

Asbestos and other carcinogens

People who have certain jobs (such as those who work in the construction and chemical industries) have an increased risk of lung cancer. Exposure to asbestos, arsenic, chromium, nickel, soot, tar, and other substances can cause lung cancer. The risk is highest for those with years of exposure. The risk of lung cancer from these carcinogensAny substance that causes cancer is even higher for smokers. It is important to follow all of the safety guidelines provided by your employer. It is also a good idea to check with your doctor about any additional precautions you should take if you are exposed to these substances at work.^5,6

Air pollution

Outdoor air pollution, which can include, among other pollutants, diesel fumes, dust, and solvents as well as particulate matter (a mixture of very small solid particles and liquid droplets, such as sulfur dioxide, soot, and many others)  may increase the risk of lung cancer. The risk from air pollution is higher for smokers. Because most sources of air pollution cannot be controlled by individuals, it is policymakers who must take steps to reduce it.^7,8

Indoor air pollution is also a risk, specifically for those who cook and/or heat their homes with kerosene fuels, coal, and biomass (organic matter used as fuel).^7,8

Family or personal history of lung cancer

People with an immediate family member—father, mother, brother, sister, son, or daughter—who has had lung cancer may be at increased risk for developing lung cancer. This is particularly the case when more than one family member is or has been affected by the disease or if a relative was diagnosed at a young age. The increased risk may be due to exposure to the same environmental risk factors, including tobacco smoke, or possibly, in rare cases, to an inherited mutation.^1,9,10,11

People who have had lung cancer themselves are at increased risk of developing a second lung tumor; this is more likely among smokers.¹

Radiation therapy

People who have had radiation therapy to the chest for cancers other than lung cancers have a higher risk of developing lung cancer. These include those who have been treated for Hodgkin lymphoma and women with breast cancer who were treated with radiation after a mastectomy.The lung cancer may take many years to develop.  Note that modern radiation therapy techniques and practices may be able to reduce this risk, but it is still a risk to be discussed with your doctor.^{1,12,13,14,15}

Age 65 and older

Age is a factor in lung cancer risk. More than two-thirds of people diagnosed with lung cancer are 65 years or older when diagnosed.¹⁶

History of lung disease

Having chronic obstructive pulmonary disease (COPD), including emphysema,  or pulmonary fibrosis, which causes scarring in lung tissue, increases lung cancer risk. In both cases, smoking increases the risk.^11,17,18

Diet

Drinking water from public sources is tested to ensure that the level of arsenic is below that which could cause any adverse effects, but arsenic in drinking water from private sources, e.g., wells, can increase lung cancer risk; this water should be tested.¹⁹

There has been some evidence to show that smokers and those who have been exposed to asbestos who take high-dose beta-carotene supplements over a long period of time are more likely to develop lung cancer, so these supplements should be avoided. This is not the case for foods that are high in beta-carotene; these foods are considered safe.²⁰