What is asbestos?
Asbestos is a group of minerals that occur naturally as bundles of fibers. These fibers, found in soil and rocks in many parts of the world, are made of silicon, oxygen, and other elements. There are 2 main types of asbestos fibers:
- Serpentine asbestos fibers are curly. The most common asbestos in industrial use, known as chrysotile, or white asbestos, has curly fibers.
- Amphibole asbestos fibers are straight and needle-like. There are several types of amphibole fibers, including amosite, crocidolite, tremolite, actinolite, and anthophyllite.
Amphiboles (particularly crocidolite) are considered to be more likely to cause cancer, but even the more commonly used chrysotile fibers have been linked to cancer.
Asbestos fibers are strong, resistant to heat and to many chemicals, and do not conduct electricity. As a result, asbestos has been used as an insulating material since ancient times. Since the industrial revolution, asbestos has been used to insulate factories, schools, homes, and ships, and to make automobile brake and clutch parts, roofing shingles, ceiling and floor tiles, cement, textiles, and hundreds of other products.
During the first half of the 1900s, growing evidence showed that breathing in asbestos caused scarring of the lungs. In the early 1900s, exposure to asbestos dust in the workplace was not controlled. Beginning in England in the 1930s, steps were taken to protect workers in the asbestos industry by installing ventilation and exhaust systems. However, in the huge shipbuilding effort during World War II, large numbers of workers were exposed to high levels of asbestos.
As asbestos-related cancers became better recognized in the second half of the 20th century, measures were taken to reduce exposure, including establishing exposure standards. In addition to more careful handling, there has been a dramatic decrease in the import and use of asbestos since the mid-1960s, and alternative insulating materials have been developed. As a result, asbestos exposure has dropped dramatically in the United States. However, it is still used in some products, and there is still a potential for exposure to asbestos in older buildings, water pipes, and other settings. Heavier asbestos use continues in many other countries as well.
How are people exposed to asbestos?
People are exposed to asbestos mainly by inhaling fibers in the air they breathe. This may occur during mining and processing asbestos, making asbestos-containing products, or installing asbestos insulation. It may also occur when older buildings are demolished or renovated, or when older asbestos-containing materials begin to break down. In any of these situations, asbestos fibers tend to create a dust composed of tiny particles that can float in the air.
In addition, asbestos fibers can be swallowed. This may happen when people consume contaminated food or liquids (such as water that flows through asbestos cement pipes). It may also occur when people cough up asbestos they have inhaled, and then swallow their saliva.
Many people are exposed to very low levels of naturally occurring asbestos in outdoor air as a result of erosion of asbestos-bearing rocks. The potential for such exposure is higher in areas where rocks have higher asbestos content. In some areas, asbestos may be detected in the water supply as well as in the air. It may be released into the water through several sources, such as erosion or natural deposits, corrosion from asbestos cement pipes, and the break down of roofing materials containing asbestos that are then transported into sewers.
However, the people with the heaviest exposure are those who worked in asbestos industries, such as shipbuilding and insulation. Many of these people recall working in thick clouds of asbestos dust, day after day.
Family members of asbestos workers can also be exposed to higher levels of asbestos because the fibers can be carried home on the workers' clothing, and can then be inhaled by others in the household.
Exposure to asbestos is also a concern in older buildings. If building materials like insulation and ceiling and floor tiles begin to decompose over time, asbestos fibers can be found in indoor air and may pose a health threat. There is no health risk if the asbestos is bonded into intact finished products, such as walls and tiles. As long as the material is not damaged or disturbed (for example, by drilling or remodeling), the fibers are not released into the air. Maintenance workers who sweep up and dispose of the asbestos dust or handle damaged asbestos-containing materials are often exposed to higher levels than other occupants of these buildings. Removing asbestos from homes and other buildings can also cause some exposure, although modern asbestos abatement workers are trained to use appropriate protective equipment to minimize exposure.
Although use of asbestos has declined in many developed countries, its use is still a health hazard in some other parts of the world. Much of the world's asbestos production is used in Eastern Europe, Latin America, and Asia, and its use is on the rise in many of these areas. In 2005, the World Health Organization estimated that 125 million people worldwide were exposed to asbestos at work, despite the known links to cancer and other lung diseases for more than 60 years.
Does asbestos cause cancer?
Evidence from studies in both people and laboratory animals has shown that asbestos can increase the risk for some types of cancer.
When asbestos fibers in the air are inhaled, they may stick to mucus in the throat, trachea (windpipe), or bronchi (large breathing tubes of the lungs) and may be cleared by being coughed up or swallowed. But some fibers may reach the ends of the small airways in the lungs or penetrate into the outer lining of the lung and chest wall (known as the pleura). These fibers may irritate the cells in the lung or pleura and eventually cause lung cancer or mesothelioma.
Studies in people
Inhalation of asbestos fibers has been linked to an increased risk of lung cancer in many studies of asbestos-exposed workers. In general, the greater the exposure to asbestos, the higher the risk of lung cancer. Most cases of lung cancer in asbestos workers occur at least 15 years after initial exposure to asbestos.
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.
Mesothelioma is a rare form of cancer that affects the thin membranes lining organs in the chest (pleura) and abdomen (peritoneum). Mesothelioma is closely linked with asbestos; most cases of mesothelioma result from direct exposure to asbestos at work.
Studies have found an increased risk of mesothelioma among workers who are exposed to asbestos, as well as among their family members and people living in the neighborhoods surrounding asbestos factories and mines. Although the risk of developing mesothelioma increases with the amount of asbestos exposure, there is no way to measure the minimum amount of asbestos exposure that can lead to mesothelioma. However, mesothelioma is very rare in the general population of the United States.
Mesotheliomas typically take a long time to develop. The time between first exposure to asbestos and diagnosis of mesothelioma is usually 30 years or more. Unfortunately, the risk of mesothelioma does not drop with time after exposure to asbestos. The risk appears to be lifelong.
Unlike lung cancer, mesothelioma risk is not increased among smokers.
Other types of cancer
Studies have also linked workplace exposure to asbestos with cancers of the larynx (voice box) and ovaries. Some studies have also suggested that workplace asbestos exposure may be linked to other cancers, including cancers of the esophagus, stomach, colon, and kidney. However, researchers aren't yet sure if all of these cancers are truly related to asbestos exposure. It's not clear exactly how asbestos might affect risk for these cancers, but swallowed asbestos fibers might somehow contribute to the risk.
Studies done in the lab
Tests on several different rodent species, using different methods of exposure, have confirmed that asbestos causes cancer in animals. All commercial forms of asbestos have produced tumors in animals. The size and shape of the asbestos fibers influence the incidence of tumors: smaller, straighter fibers seem more hazardous, perhaps because they are more likely to reach the deepest parts of the lungs.
What expert agencies say
Several agencies (national and international) study different substances in the environment to determine if they can cause cancer. (A substance that causes cancer or helps cancer grow is called a carcinogen.) The American Cancer Society looks to these organizations to evaluate the risks based on evidence from laboratory, animal, and human research studies.
Based on animal and human evidence like the examples above, several expert agencies have evaluated the cancer-causing nature of asbestos.
The International Agency for Research on Cancer (IARC) is part of the World Health Organization (WHO). Its major goal is to identify causes of cancer. Based on the data available, IARC classifies asbestos as "carcinogenic to humans".
The National Toxicology Program (NTP) is formed from parts of several different US government agencies, including the National Institutes of Health (NIH), the Centers for Disease Control and Prevention (CDC), and the Food and Drug Administration (FDA). The NTP has classified asbestos as "known to be a human carcinogen".
The US Environmental Protection Agency (EPA) maintains the Integrated Risk Information System (IRIS), an electronic database that contains information on human health effects from exposure to various substances in the environment. The EPA classifies asbestos as a human carcinogen.
(For more information on the classification systems used by these agencies, see our document, Known and Probable Human Carcinogens.)
Does asbestos cause any other health problems?
The major health problem caused by asbestos exposure, aside from cancer, is a lung disease called asbestosis. When a person breathes high levels of asbestos over time, some of the fibers lodge deep in the lungs. Irritation caused by the fibers eventually leads to scarring (fibrosis) in the lungs. This can make it hard to breathe. The main symptoms of asbestosis are shortness of breath and a chronic cough.
When asbestosis occurs, it is typically 10 to 20 years after the initial exposure to asbestos. The disease can get worse over time. While some people may not have serious symptoms, others may be seriously disabled by breathing problems. Unfortunately there is no effective treatment for this disease.
Asbestos can also reach the outer lining of the lungs (pleura), where it can cause pleural plaques (areas of hard, scar-like tissue in the pleura), pleural thickening, and pleural effusions (buildup of fluid between the lungs and the pleura). All of these conditions can make it harder to breathe.
How can I avoid exposure to asbestos?
If there is a possibility you may be exposed to asbestos at work, such as during renovating old buildings, then you should use all protective equipment, work practices, and safety procedures designed for working around asbestos. If you are concerned about asbestos exposure in your workplace, discuss the situation with your employee health and safety representative or your employer. If needed, the Occupational Safety & Health Administration (OSHA), the federal agency responsible for health and safety regulations in most workplaces, can provide more information or make an inspection.
If you live in an older home, there may be asbestos-containing insulation or other materials. A knowledgeable expert can check your home to determine if there is any asbestos and if it poses any risk of exposure. This may involve testing the air for asbestos levels. (Again, just because asbestos exists in a home does not necessarily mean that it needs to be removed. As long as the material is not damaged or disturbed, for example by drilling or remodeling, the fibers are not released into the air.) If asbestos needs to be removed from your home, you should hire a qualified contractor to perform this job to avoid contaminating your home further or causing any exposure to your family or to the workers. You should not attempt to remove asbestos-containing material yourself.
What should I do if I've been exposed to asbestos?
If you have been exposed to asbestos, it is important to assess the amount of your exposure. If you were exposed only very briefly, or only at very low levels, your risk of a resulting disease is probably low. However, it you were exposed at high levels or for long periods of time, you may be at increased risk of certain cancers or the other diseases discussed above. You can protect your health in several ways:
- If you are a smoker, it is very important that you try to stop smoking. Evidence suggests that asbestos-exposed workers who quit smoking can significantly reduce their risk of developing lung cancer.
- Talk to your doctor about whether you should get regular health checkups to look for signs of asbestos-related diseases. You may want to ask about seeing a doctor experienced with asbestos-related diseases. Some doctors recommend that people with heavy asbestos exposure get regular chest x-rays or CT scans and lung function tests. These tests can't detect asbestos fibers themselves, but they may be able to detect problems that could be caused by the fibers.
- Tell your doctor if you start to have symptoms that might be related to asbestos exposure such as shortness of breath, a new or worsening cough, pain or tightness in the chest, trouble swallowing, or unintended weight loss. See your doctor promptly for any respiratory illness.
- Ask your doctor about getting vaccines against flu and pneumonia.
If you've already been diagnosed with an asbestos-related disease, there are some places you may be able to go for financial help with treatment. Some people with asbestos-related illness may be eligible for Medicare coverage. Some people also may qualify for help, including medical payments, under state workers' compensation laws. Because eligibility requirements vary from state to state, workers should contact their state workers' compensation board. Eligible veterans may receive health care at a Department of Veterans Affairs (VA) Medical Center for asbestos-related diseases.
More information from your American Cancer Society
The following related information may also be helpful to you. These materials may be viewed on our web site or ordered from our toll-free number, at 1-800-227-2345.
National organizations and Web sites*
In addition to the American Cancer Society, other sources of information and support include:
National Cancer Institute (NCI)
Toll-free number: 1-800-422-6237 (1-800-4-CANCER)
Web site : www.cancer.gov
Asbestos exposure and cancer risk: www.cancer.gov/cancertopics/factsheet/Risk/asbestos
No matter who you are, we can help. Contact us anytime, day or night, for information and support. Call us at 1-800-227-2345 or visit www.cancer.org.
Agency for Toxic Substances and Disease Registry. Asbestos: Health Effects. 2008. Accessed at www.atsdr.cdc.gov/asbestos/asbestos/health_effects/index.html on January 12, 2010.
International Agency for Research on Cancer. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Supplement 7: Overall Evaluations of Carcinogenicity: An Updating of IARC Monographs Volumes 1 to 42. 1987. Accessed at http://monographs.iarc.fr/ENG/Monographs/suppl7/Supp7-24.pdf on January 12, 2010.
Straif K, Benbrahim-Tallaa L, Baan R, et al, for the WHO International Agency for Research on Cancer Monograph Working Group. A review of human carcinogens--part C: metals, arsenic, dusts, and fibres. Lancet Oncol. 2009;10:453−454.
US Department of Health and Human Services. Public Health Service, National Toxicology Program. Report on Carcinogens, Eleventh Edition. 2005. Accessed at http://ntp.niehs.nih.gov/index.cfm?objectid=32BA9724-F1F6-975E-7FCE50709CB4C932 on January 12, 2010.
US Environmental Protection Agency. Integrated Risk Information System: Asbestos (CASRN 1332-21-4). 1993. Accessed at www.epa.gov/ncea/iris/subst/0371.htm on January 12, 2010.
US National Cancer Institute. Asbestos Exposure and Cancer Risk. 2009. Accessed at www.cancer.gov/cancertopics/factsheet/Risk/asbestos on January 11, 2010.
Last Revised: 05/10/2013