A risk factor is anything that affects a person's chance of getting a disease such as cancer. Different cancers have different risk factors. For example, unprotected exposure to strong sunlight is a risk factor for skin cancer.

But risk factors don't tell us everything. Having a risk factor, or even several risk factors, does not mean that you will get the disease. And many people who get the disease may not have had any known risk factors. Even if a person with lung cancer has a risk factor, it is often very hard to know how much that risk factor may have contributed to the cancer.

Several risk factors can make you more likely to develop lung cancer:

Tobacco smoke

Smoking is by far the leading risk factor for lung cancer. In the early 20th century, lung cancer was much less common than some other types of cancer. But this changed once manufactured cigarettes became readily available.

About 87% of lung cancer deaths are thought to result from smoking. The risk for lung cancer among smokers is many times higher than among non-smokers. The longer you smoke and the more packs a day you smoke, the greater your risk.

Cigar smoking and pipe smoking are almost as likely to cause lung cancer as cigarette smoking. Smoking low tar or "light" cigarettes increases lung cancer risk as much as regular cigarettes. There is concern that mentholated cigarettes may increase the risk even more since the menthol allows smokers to inhale more deeply.

If you stop smoking before a cancer develops, your damaged lung tissue gradually starts to repair itself. No matter what your age or how long you've smoked, quitting may help you live longer. People who stop smoking before age 50 cut their risk of dying in the next 15 years in half compared with those who continue to smoke. For help quitting, see our Guide to Quitting Smoking or call the American Cancer Society at 1-800-227-2345.

Secondhand smoke: If you don't smoke, breathing in the smoke of others (called secondhand smoke or environmental tobacco smoke) can increase your risk of developing lung cancer. A non-smoker who lives with a smoker has about a 20% to 30% greater risk of developing lung cancer. Workers who have been exposed to tobacco smoke in the workplace are also more likely to get lung cancer. Secondhand smoke is thought to cause more than 3,000 deaths from lung cancer each year.

Some evidence suggests that certain people are more susceptible to the cancer-causing effect of tobacco smoke than others.

Radon

Radon is a naturally occurring radioactive gas that results from the breakdown of uranium in soil and rocks. It cannot be seen, tasted, or smelled. According to the U.S. Environmental Protection Agency (EPA), radon is the second leading cause of lung cancer, and is the leading cause among non-smokers.

Outdoors, there is so little radon that it is not dangerous. But indoors, radon can be more concentrated and become a possible risk for cancer. Houses in some parts of the United States built on soil with natural uranium deposits can have high indoor radon levels (especially in basements). Studies from these areas have found that the risk of lung cancer is higher in those who have lived for many years in a radon-contaminated house.

The lung cancer risk from radon is much lower than that from tobacco smoke. However, the risk from radon is much higher in people who smoke than in those who don't.

If you are concerned about radon exposure, state and local offices of the EPA can give you the names of reliable companies that perform radon testing and renovation. For more information, see the document, Radon.

Asbestos

Workplace exposure to asbestos fibers is an important risk factor for lung cancer. Studies have found that people who work with asbestos (in some mines, mills, textile plants, places where insulation is used, shipyards, etc.) are several times more likely to die of lung cancer. In workers exposed to asbestos who also smoke, the lung cancer risk is much greater than even adding the risks from these exposures separately. It's not clear to what extent low-level or short-term exposure to asbestos might raise lung cancer risk.

Both smokers and non-smokers exposed to asbestos also have a greater risk of developing mesothelioma, a type of cancer that starts in the pleura (the lining surrounding the lungs). Because it is not usually considered a type of lung cancer, mesothelioma is discussed in the document, Malignant Mesothelioma.

In recent years, government regulations have greatly reduced the use of asbestos in commercial and industrial products. It is still present in many homes and commercial buildings but is not usually considered harmful as long as it is not released into the air by deterioration, demolition, or renovation. For more information, see the document, Asbestos.

Other cancer-causing agents in the workplace

Other carcinogens (cancer-causing agents) found in some workplaces that can increase lung cancer risk include:

• radioactive ores such as uranium

• inhaled chemicals or minerals such as arsenic, beryllium, cadmium, silica, vinyl chloride, nickel compounds, chromium compounds, coal products, mustard gas, and chloromethyl ethers

• diesel exhaust

The government and industry have taken steps in recent years to protect workers. But the dangers are still present, and if you work around these agents, you should be careful to limit your exposure whenever possible.

Radiation therapy to the lungs

People who have had radiation therapy to the chest for cancer are at higher risk for lung cancer, particularly if they smoke. Typical patients are those treated for Hodgkin disease or women who get radiation after a mastectomy for breast cancer. Women who receive radiation therapy to the breast after a lumpectomy do not appear to have a higher than expected risk of lung cancer.

Arsenic

High levels of arsenic in drinking water may increase the risk of lung cancer. This is even more pronounced in smokers.

Personal or family history of lung cancer

If you have had lung cancer, you have a higher risk of developing another lung cancer. Brothers, sisters, and children of those who have had lung cancer may have a slightly higher risk of lung cancer themselves, especially if it was diagnosed when the relative was younger. It is not clear how much of this risk might be due to genetics and how much might be from shared exposures (such as tobacco smoke or radon).

Researchers have found that genetics does seem to play a role in some families with a strong history of lung cancer. People who inherit certain DNA changes in a particular chromosome (chromosome 6) are more likely to develop lung cancer, even if they only smoke a little. At this time these DNA changes cannot be routinely tested for. Research is ongoing in this area.

Certain dietary supplements

Studies looking at the possible role of antioxidant supplements in reducing lung cancer risk have not been promising thus far. In fact, 2 large studies found that smokers who took beta carotene supplements actually had an increased risk of lung cancer. The results of these studies suggest that smokers should avoid taking beta carotene supplements.

Air pollution

In cities, air pollution (especially from heavily trafficked roads) appears to raise the risk of lung cancer slightly. This risk is far less than the risk caused by smoking, but some researchers estimate that worldwide about 5% of all deaths from lung cancer may be due to outdoor air pollution.

Factors with uncertain or unproven effects on lung cancer risk

Marijuana: There are some reasons to think that marijuana smoking might increase lung cancer risk. Marijuana contains more tar than cigarettes. (Tar is the sticky, solid material that remains after burning, which is thought to contain most of the harmful substances in smoke.) Marijuana is also inhaled very deeply and the smoke is held in the lungs for a long time. Marijuana is smoked all the way to the end where tar content is the highest. Many of the cancer-causing substances in tobacco are also found in marijuana. And because marijuana is an illegal substance, it is not possible to control what other substances it might contain.

But it has been hard to study whether there is a link between marijuana and lung cancer because it is not easy to gather information about the use of illegal drugs. Also, many marijuana smokers also smoke cigarettes. This makes it hard to know how much of the risk is from tobacco and how much might be from marijuana. In the very limited studies done so far, marijuana use has not been strongly linked to lung cancer, but more research in this area is needed.

Talc and talcum powder: Talc is a mineral that in its natural form may contain asbestos. In the past, some studies suggested that talc miners and millers have a higher risk of lung cancer and other respiratory diseases because of their exposure to industrial grade talc. Recent studies of talc miners have not found an increase in lung cancer rate.

Talcum powder is made from talc. By law since 1973, all home-use talcum products (baby, body, and facial powders) have been asbestos-free. The use of cosmetic talcum powder has not been found to increase the risk of lung cancer.

Last Medical Review: 10/20/2009
Last Revised: 10/20/2009