A risk factor is anything that affects a person's chance ofgetting a disease such as cancer. Different cancers have different risk factors. Some risk factors, like smoking, can be controlled. Others, like a person's age or family history, can't be changed.

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. Still, having several risk factors can make you more likely to get lung cancer.

Tobacco smoke

Smoking is by far the leading risk factor for lung cancer. Tobacco smoke causes nearly 9 out of 10 cases of lung cancer. The longer a person has been smoking and the more packs per day smoked, the greater the risk. If a person stops smoking before lung cancer starts, the lung tissue slowly returns to normal. Stopping smoking at any age lowers the risk of lung cancer.

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

Secondhand smoke: People who don't smoke but who breathe the smoke of others may also be at a higher risk for lung cancer. Non-smoking spouses who live with a smoker, for instance, have about a 20% to 30% greater risk of developing lung cancer than do spouses of non-smokers. Non-smokers exposed to tobacco smoke in the workplace are also more likely to get lung cancer. Some people seem to be more prone to the cancer-causing effect of tobacco smoke than others.

Radon

Radon is a radioactive gas made by the natural breakdown of uranium in soil and rocks. Uranium is found at higher than normal levels in the soil in some parts of the United States. Radon can't be seen, tasted, or smelled. It can build up indoors and create a possible risk for cancer. The risk is much higher among smokers than for those that don't. State and local offices of the EPA (Environmental Protection Agency) can give you information on how to test for radon in the home. The document, Radon, is also available from the ACS.

Asbestos

Asbestos is another risk factor for lung cancer. People who work with asbestos have a higher risk of getting lung cancer. If they also smoke, the risk is greatly increased. Both smokers and non-smokers exposed to asbestos also have a greater risk of getting a type of cancer called mesothelioma, which starts in the lining of the lungs. Although asbestos was used for many years, the government has now nearly stopped its use in the workplace and in home products. While it is still present in many buildings, it is not thought to be harmful as long as it is not released into the air. To learn more, see our document, Asbestos.

Other cancer-causing things in the workplace

Other things that cause cancer (carcinogens) found in some workplaces that can increase lung cancer risk include:

• Rradioactive ores, such as uranium
• Inhaled chemicals or minerals, such as arsenic, beryllium, cadmium, vinyl chloride, nickel compounds, chromium compounds, coal products, mustard gas, and chloromethyl ethers
• Diesel exhaust

The government and industry have taken major steps in recent years to protect workers. But the dangers are still there. If you work around any of these, you should be very careful to limit your exposure as much as you can.

Radiation treatment to the lungs

People who have had radiation to the chest to treat another cancer are at higher risk for lung cancer, especially if they smoke. Women who have radiation to the breast after a lumpectomy for breast cancer do not appear to have a higher risk of lung cancer.

Arsenic

High levels of arsenic in drinking water may increase the risk of lung cancer. The effect is even greater for smokers.

Personal and family history

If you have had lung cancer, you have a higher risk of getting another lung cancer. Brothers, sisters, and children of people who have had lung cancer may have a slightly higher risk themselves. Researchers have found that genes do seem to play a role in some families with a strong history of lung cancer.  More research is being done on this.

Diet and vitamins

Studies looking at the possible role of some supplements in reducing lung cancer risk have not shown promise thus far.  In fact, 2 studies have 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 not take beta carotene supplements.

Air pollution

In cities, air pollution may slightly increase the risk of lung cancer. But the risk is still far less than that caused by smoking. Worldwide, about 5% of all deaths from lung cancer may be due to outdoor air pollution.

Marijuana

There are some reasons to think that marijuana could cause cancers of the mouth and throat. 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. And many marijuana smokers also smoke cigarettes. Marijuana cigarettes have more tar than regular cigarettes. Many of the cancer-causing substances in tobacco are also found in marijuana. Marijuana is inhaled very deeply and the smoke is held in the lungs for a long time. For these reasons it is thought that smoking marijuana could increase lung cancer risk. 

DNA and gene changes

During the past few years, scientists have made great progress in understanding how risk factors produce certain changes in the DNA of lung cells, causing the cells to become cancer. DNA is the genetic material that carries the instructions for nearly everything our cells do.

Current research in this field is aimed at developing tests that can find lung cancers at an early stage by spotting DNA changes. But these tests are not yet ready for routine use. For now, doctors stress the importance of not using tobacco and staying away from other things that can increase your cancer risk.

Last Medical Review: 11/18/2009
Last Revised: 11/18/2009