Benzene is a colorless, flammable liquid with a sweet odor. It evaporates quickly when exposed to air. Benzene is formed from natural processes, such as volcanoes and forest fires, but most exposure to benzene results from human activities.
Benzene is among the 20 most widely used chemicals in the United States. It is used mainly as a solvent (a substance that can dissolve or extract other substances) and as a starting material in making other chemicals. In the past it was also commonly used as a gasoline additive, but this use has been greatly reduced in recent decades.
Benzene is also a natural part of crude oil, gasoline, and cigarette smoke.
How are people exposed to benzene?
The main route of exposure to benzene is by inhaling contaminated air. Benzene can also be absorbed through the skin during contact with a source such as gasoline, but because liquid benzene evaporates quickly, skin absorption is less common.
People can be exposed to benzene at work, in the general environment, and through the use of some consumer products. The highest exposures have typically been in workplace, although these have decreased greatly over the last several decades due to federal regulations. Other exposures have also gone down over time, such as the amount of benzene allowed in gasoline.
Workers in industries that make or use benzene may be exposed to high levels of this chemical. These industries include the rubber industry, oil refineries, chemical plants, shoe manufacturers, and gasoline-related industries. Benzene is also used to make some types of lubricants, dyes, detergents, drugs, and pesticides. Other people who may be exposed to benzene at work include steel workers, printers, lab technicians, and firefighters. Federal regulations limit exposure to benzene in the workplace (see below).
Sources of benzene in the environment include gasoline, automobile exhaust fumes, emissions from some factories, and waste water from certain industries. While benzene is commonly found in air in both urban and rural areas, the levels are usually very low. However, exposures can be substantial to people in enclosed spaces with unventilated fumes from gasoline, glues, solvents, paints, and art supplies. Areas of heavy traffic, gas stations, and areas near industrial sources may also have higher air levels.
Cigarette smoking and secondhand smoke are important sources of exposure to benzene. Cigarette smoke accounts for about half of the US national exposure to benzene. Benzene levels in rooms contaminated by tobacco smoke may be many times higher than normal.
People can also be exposed to benzene in contaminated drinking water and some foods (see regulations below).
Does benzene cause cancer?
Benzene is known to cause cancer, based on evidence from studies in both people and laboratory animals. The link between benzene and cancer has largely focused on leukemia and cancers of other blood cells.
Studies in people
Rates of leukemia, particularly acute myeloid leukemia (AML), have been found to be higher in studies of workers exposed to high levels of benzene, such as those in the chemical, shoemaking, and oil refining industries.
Some studies have also suggested links to acute lymphocytic leukemia (ALL) in children and to chronic lymphocytic leukemia (CLL) and other blood-related cancers, such as multiple myeloma and non-Hodgkin lymphoma, in adults. However, the evidence is not as strong for these cancers.
Studies done in the lab
Benzene has also been studied for its ability to cause cancer in lab animals such as rats and mice. When inhaled or swallowed, benzene has been found to cause various types of tumors in lab animals. These results support the finding of an excess risk of leukemia in humans from exposure to benzene, However, most studies in humans have not found an increased risk of cancers other than leukemia among people with higher exposures.
Benzene has been shown to cause chromosome changes in bone marrow cells in the lab. Such changes are commonly found in human leukemia cells.
What expert agencies say
Several agencies (national and international) study review and evaluate the evidence to determine whether chemicals 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, several expert agencies have evaluated the cancer-causing potential of benzene.
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 benzene as a “known human carcinogen”, with “sufficient” evidence that benzene causes acute myeloid leukemia (AML). The evidence for acute lymphocytic leukemia (ALL), chronic lymphocytic leukemia (CLL), multiple myeloma, and non-Hodgkin lymphoma is designated as “limited”.
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 benzene 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 benzene as a known human carcinogen.
(For more information on the classification systems used by these agencies, see our document, Known and Probable Human Carcinogens.)
Does benzene cause any other health problems?
Benzene is a potentially dangerous chemical. High levels of exposure can cause both short-term and long-term health effects.
Breathing in high doses of benzene may affect the central nervous system, which can lead to drowsiness, dizziness, headaches, tremors, confusion, and/or unconsciousness. Consuming foods or fluids contaminated with high levels of benzene can cause vomiting, stomach irritation, dizziness, sleepiness, convulsions, and rapid heart rate. In extreme cases, death may occur after inhaling or swallowing very high levels of benzene.
Exposure to benzene liquid or vapor may irritate the skin, eyes, and throat. Skin exposure to benzene may result in redness and blisters.
Long-term exposure to benzene primarily harms the bone marrow, the soft, inner parts of bones where new blood cells are made. This may result in:
- Anemia (a low red blood cell count), which can cause a person to feel weak and tired.
- A low white blood cell count, which can lower the body’s ability to fight infections and may even be life-threatening.
- A low blood platelet count, which can lead to excessive bleeding.
There is also some evidence that long-term exposure to benzene may harm reproductive organs. Some women who have breathed high levels of benzene for many months have had irregular menstrual periods and ovary shrinkage, but it is not known for certain if benzene caused these effects. It is not known if benzene exposure affects the fetus in pregnant women or fertility in men.
Are benzene levels regulated?
Several government agencies regulate benzene levels and exposures.
The Occupational Safety & Health Administration (OSHA), the federal agency responsible for health and safety regulations in most workplaces, limits workplace exposure to benzene in the air to 1 ppm (part per million) during an average workday and a maximum of 5 ppm over any 15-minute period. When working at potentially higher exposure levels, OSHA requires employers to provide personal protective equipment such as respirators.
The EPA limited the percentage of benzene allowed in gasoline to an average of 1% (with a maximum of 5%) as of 1990. As of 2011, this limit is further reduced to an average of 0.62% (with a maximum of 1.3%).
The EPA limits concentrations of benzene in drinking water to 5 ppb (parts per billion). Some states may have lower limits. Likewise, the US Food and Drug Administration (FDA) set a limit of 5 ppb in bottled water.
Can I limit my exposure to benzene?
If you are concerned about benzene, there are several ways you can limit your exposure.
If you are exposed on the job, talk to your employer about limiting exposures through process changes (such as replacing the benzene with another solvent or enclosing the benzene source) or by using personal protective equipment. If needed, the Occupational Safety & Health Administration (OSHA) can provide more information or make an inspection.
Stay away from cigarette smoke. If you are a smoker, try to quit. Cigarette smoke is a major source of benzene exposure.
Try to limit gasoline fumes by pumping gas carefully and choosing gas stations with vapor recovery systems that capture the fumes. Avoid skin contact with gasoline.
Finally, use common sense around any chemicals that might contain benzene. Minimize or avoid exposure to fumes from solvents, paints, and art supplies, especially in unventilated spaces.
What should I do if I’ve been exposed to benzene?
For short-term exposure to high levels of benzene, the Centers for Disease Control and Prevention (CDC) recommends getting away from the source of benzene, removing any clothing that may have benzene on it, washing exposed areas with soap and water, and getting medical care as soon as possible.
If you think you may have been exposed to benzene over a long period of time, speak to a doctor. Benzene can be measured in the blood or breath, and breakdown products of benzene can be measured in the urine. These tests can only detect recent exposures to benzene. They cannot predict possible health effects.
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:
Environmental Protection Agency (EPA)
Toll-free number (Safe Drinking Water Hotline): 1-800-426-4791
Web site: www.epa.gov
Benzene in drinking water: www.epa.gov/safewater/contaminants/basicinformation/benzene.html
National Cancer Institute (NCI)
Toll-free number: 1-800-422-6237 (1-800-4-CANCER)
Web site: www.cancer.gov
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. ToxFAQs for Benzene. 2007. Accessed at www.atsdr.cdc.gov/tfacts3.html on January 15, 2010.
Baan R, Grosse Y, Straif K, et al., for the WHO International Agency for Research on Cancer Monograph Working Group. A review of human carcinogens–Part F: chemical agents and related occupations. Lancet Oncol. 2009;10:1143−1144.
Centers for Disease Control and Prevention. Facts About Benzene. Accessed at www.bt.cdc.gov/agent/benzene/basics/facts.asp on January 20, 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/Suppl7-20.pdf on January 19, 2010.
International Agency for Research on Cancer (IARC). IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Vol. 29: Some Industrial Chemicals and Dyestuffs. 1982. Accessed at http://monographs.iarc.fr/ENG/Monographs/vol29/volume29.pdf on January 19, 2010.
Occupational Safety and Health Administration. Occupational exposure to benzene. Final Rule. Federal Register. 1987;52:34460−34578.
Rinsky RA, Smith AB, Hornung R, et al. Benzene and leukemia: an epidemiological risk assessment. New Engl J Med. 1987;316:1044−1050.
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/ntp/roc/eleventh/profiles/s019benz.pdf on January 19, 2010.
US Environmental Protection Agency. Integrated Risk Information System: Benzene (CASRN 71-43-2). 2003. Accessed at www.epa.gov/ncea/iris/subst/0276.htm on January 19, 2010.
US National Library of Medicine. Tox Town: Benzene. 2009. Accessed at http://toxtown.nlm.nih.gov/text_version/chemicals.php?id=5 on January 19, 2010.
courtesy of CDC website