1. What is secondhand smoke?

Secondhand smoke (also called environmental tobacco smoke) is the combination of sidestream smoke (the smoke given off by the burning end of a tobacco product) and mainstream smoke (the smoke exhaled by the smoker) (1, 2, 3, 4). Exposure to secondhand smoke is also called involuntary smoking or passive smoking. People are exposed to secondhand smoke in homes, cars, the workplace, and public places such as bars, restaurants, and other recreation settings. In the United States, the source of most secondhand smoke is from cigarettes, followed by pipes, cigars, and other tobacco products (4).

2. How is secondhand smoke exposure measured?

Secondhand smoke is measured by testing indoor air for nicotine or other smoke constituents. Exposure to secondhand smoke can be tested by measuring the levels of cotinine (a nicotine by-product in the body) in the nonsmoker’s blood, saliva, or urine (1). Nicotine, cotinine, carbon monoxide, and other evidence of secondhand smoke exposure have been found in the body fluids of nonsmokers exposed to secondhand smoke.

3. Does secondhand smoke contain harmful chemicals?

Yes. Of the more than 4,000 chemicals that have been identified in secondhand tobacco smoke, at least 250 are known to be harmful, and 50 of these are known to cause cancer. These chemicals include (1):

• arsenic (a heavy metal toxin)
• benzene (a chemical found in gasoline)
• beryllium (a toxic metal)
• cadmium (a metal used in batteries)
• chromium (a metallic element)
• ethylene oxide (a chemical used to sterilize medical devices)
• nickel (a metallic element)
• polonium–210 (a chemical element that gives off radiation)
• vinyl chloride (a toxic substance used in plastics manufacture)

Many factors affect which chemicals are found in secondhand smoke, including the type of tobacco, the chemicals added to the tobacco, the way the product is smoked, and the paper in which the tobacco is wrapped (1, 3, 4).

4. Does exposure to secondhand smoke cause cancer?

Yes. The U.S. Environmental Protection Agency (EPA), the U.S. National Toxicology Program (NTP), the U.S. Surgeon General, and the International Agency for Research on Cancer (IARC) have classified secondhand smoke as a known human carcinogen (cancer-causing agent) (1, 3, 5).

Inhaling secondhand smoke causes lung cancer in nonsmoking adults (4). Approximately 3,000 lung cancer deaths occur each year among adult nonsmokers in the United States as a result of exposure to secondhand smoke (2). The Surgeon General estimates that living with a smoker increases a nonsmoker’s chances of developing lung cancer by 20 to 30 percent (4).

Some research suggests that secondhand smoke may increase the risk of breast cancer, nasal sinus cavity cancer, and nasopharyngeal cancer in adults, and leukemia, lymphoma, and brain tumors in children (4). Additional research is needed to learn whether a link exists between secondhand smoke exposure and these cancers.

5. What are the other health effects of exposure to secondhand smoke?

Secondhand smoke causes disease and premature death in nonsmoking adults and children (4). Exposure to secondhand smoke irritates the airways and has immediate harmful effects on a person’s heart and blood vessels. It may increase the risk of heart disease by an estimated 25 to 30 percent (4). In the United States, secondhand smoke is thought to cause about 46,000 heart disease deaths each year (6). There may also be a link between exposure to secondhand smoke and the risk of stroke and hardening of the arteries; however, additional research is needed to confirm this link.

Children exposed to secondhand smoke are at an increased risk of sudden infant death syndrome (SIDS), ear infections, colds, pneumonia, bronchitis, and more severe asthma. Being exposed to secondhand smoke slows the growth of children’s lungs and can cause them to cough, wheeze, and feel breathless (4).

6. What is a safe level of secondhand smoke?

There is no safe level of exposure to secondhand smoke. Studies have shown that even low levels of secondhand smoke exposure can be harmful. The only way to fully protect nonsmokers from secondhand smoke exposure is to completely eliminate smoking in indoor spaces. Separating smokers from nonsmokers, cleaning the air, and ventilating buildings cannot completely eliminate secondhand smoke exposure (4).

7. What is being done to reduce nonsmokers’ exposure to secondhand smoke?

Many state and local governments have passed laws prohibiting smoking in public facilities such as schools, hospitals, airports, and bus terminals. Increasingly, state and local governments are also requiring private workplaces, including restaurants and bars, to be smoke free. To highlight the significant risk from secondhand smoke exposure, the National Cancer Institute, a component of the National Institutes of Health, holds meetings and conferences in states, counties, cities, or towns that are smoke free, unless certain circumstances justify an exception to this policy.

More information about state-level tobacco regulations is available through the Centers for Disease Control and Prevention (CDC) State Tobacco Activities Tracking and Evaluation (STATE) System Web site. The STATE System is a database containing up-to-date and historical state-level data on tobacco use prevention and control. This resource is available at http://apps.nccd.cdc.gov/statesystem/ on the Internet.

On the national level, several laws restricting smoking in public places have been passed. Federal law bans smoking on domestic airline flights, nearly all flights between the United States and foreign destinations, interstate buses, and most trains. Smoking is also banned in most Federally owned buildings. The Pro-Children Act of 1994 prohibits smoking in facilities that routinely provide Federally funded services to children.

The U.S. Department of Health and Human Services (DHHS) Healthy People 2010, a comprehensive, nationwide health promotion and disease prevention agenda, includes the goal of reducing the proportion of nonsmokers exposed to secondhand smoke from 65 percent to 45 percent by 2010 (7). More information about this program is available on the Healthy People 2010 Web site at http://www.healthypeople.gov/ on the Internet.

Internationally, several nations, including France, Ireland, New Zealand, Norway, and Uruguay, require all workplaces, including bars and restaurants, to be smoke free.

Selected References

1. National Toxicology Program. Report on Carcinogens. Eleventh Edition. U.S. Department of Health and Human Services, Public Health Service, National Toxicology Program, 2005.
2. National Cancer Institute. Cancer Progress Report 2003. Public Health Service, National Institutes of Health, U.S. Department of Health and Human Services, 2004.
3. International Agency for Research on Cancer. Tobacco Smoke and Involuntary Smoking. Lyon, France: 2002.
4. U.S. Department of Health and Human Services. The Health Consequences of Involuntary Exposure to Tobacco Smoke: A Report of the Surgeon General. Rockville, MD: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, Coordinating Center for Health Promotion, National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health, 2006.
5. U.S. Environmental Protection Agency. Respiratory Health Effects of Passive Smoking (Also Known as Exposure to Secondhand Smoke or Environmental Tobacco Smoke--ETS). U.S. Environmental Protection Agency, 1992.
6. California Environmental Protection Agency, Office of Environmental Health Hazard Assessment. Proposed Identification of Environmental Tobacco Smoke as a Toxic Air Contaminant: Part B Health Effects, 2005.
7. U.S. Department of Health and Human Services. Healthy People 2010: Understanding and Improving Health. 2nd ed. Washington, DC: U.S. Government Printing Office, 2000.

Related NCI materials and Web pages:

• National Cancer Institute Fact Sheet 10.16, Questions and Answers About Cigar Smoking and Cancer ¹
  (http://www.cancer.gov/cancertopics/factsheet/Tobacco/cigars)
• National Cancer Institute Fact Sheet 10.19, Quitting Smoking: Why To Quit and How To Get Help ²
  (http://www.cancer.gov/cancertopics/factsheet/Tobacco/cessation)
• Smoking and Tobacco Control Monograph 10: Health Effects of Exposure to Environmental Tobacco Smoke ³
  (http://cancercontrol.cancer.gov/tcrb/monographs/10/index.html)
• NCI's Smoking and Cancer Home Page ⁴
  (http://www.cancer.gov/cancertopics/smoking)

NCI’s Cancer Information Service
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Glossary Terms

A poisonous chemical used to kill weeds and pests. Also used in cancer therapy.

A chronic disease in which the bronchial airways in the lungs become narrowed and swollen, making it difficult to breathe. Symptoms include wheezing, coughing, tightness in the chest, shortness of breath, and rapid breathing. An attack may be brought on by pet hair, dust, smoke, pollen, mold, exercise, cold air, or stress.

A chemical that is used widely by the chemical industry, and is also found in tobacco smoke, vehicle emissions, and gasoline fumes. Exposure to benzene may increase the risk of developing leukemia.

A tissue with red blood cells, white blood cells, platelets, and other substances suspended in fluid called plasma. Blood takes oxygen and nutrients to the tissues, and carries away wastes.

A tube through which the blood circulates in the body. Blood vessels include a network of arteries, arterioles, capillaries, venules, and veins.

The growth of abnormal cells in the tissues of the brain. Brain tumors can be benign (non-cancerous) or malignant (cancerous).

Cancer that forms in tissues of the breast, usually the ducts (tubes that carry milk to the nipple) and lobules (glands that make milk). It occurs in both men and women, although male breast cancer is rare.

Inflammation (swelling and reddening) of the bronchi.

A metallic element that occurs naturally in tiny amounts in air, water, soil, and food. It is a byproduct of zinc refining, and is used to make batteries, pigments, plastics, alloys, and electroplate. It is also found in cigarette smoke. Exposure to high levels of cadmium may cause certain cancers and other health problems.

A term for diseases in which abnormal cells divide without control. Cancer cells can invade nearby tissues and can spread to other parts of the body through the blood and lymph systems. There are several main types of cancer. Carcinoma is cancer that begins in the skin or in tissues that line or cover internal organs. Sarcoma is cancer that begins in bone, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue. Leukemia is cancer that starts in blood-forming tissue such as the bone marrow, and causes large numbers of abnormal blood cells to be produced and enter the blood. Lymphoma and multiple myeloma are cancers that begin in the cells of the immune system. Central nervous system cancers are cancers that begin in the tissues of the brain and spinal cord.

A poisonous gas that has no color or odor. It is given off by burning fuel (as in exhaust from cars or household heaters) and tobacco products. Carbon monoxide prevents red blood cells from carrying enough oxygen for cells and tissues to live.

Any substance that causes cancer.

Smoke that comes from the burning of a tobacco product and smoke that is exhaled by smokers. Inhaling environmental tobacco smoke is called involuntary or passive smoking. Also called ETS and secondhand smoke.

Invasion and multiplication of germs in the body. Infections can occur in any part of the body and can spread throughout the body. The germs may be bacteria, viruses, yeast, or fungi. They can cause a fever and other problems, depending on where the infection occurs. When the body’s natural defense system is strong, it can often fight the germs and prevent infection. Some cancer treatments can weaken the natural defense system.

Cancer that starts in blood-forming tissue such as the bone marrow and causes large numbers of blood cells to be produced and enter the bloodstream.

Cancer that forms in tissues of the lung, usually in the cells lining air passages. The two main types are small cell lung cancer and non-small cell lung cancer. These types are diagnosed based on how the cells look under a microscope.

Cancer that begins in cells of the immune system. There are two basic categories of lymphomas. One kind is Hodgkin lymphoma, which is marked by the presence of a type of cell called the Reed-Sternberg cell. The other category is non-Hodgkin lymphomas, which includes a large, diverse group of cancers of immune system cells. Non-Hodgkin lymphomas can be further divided into cancers that have an indolent (slow-growing) course and those that have an aggressive (fast-growing) course. These subtypes behave and respond to treatment differently. Both Hodgkin and non-Hodgkin lymphomas can occur in children and adults, and prognosis and treatment depend on the stage and the type of cancer.

By or having to do with the nose.

Cancer that forms in tissues of the nasopharynx (upper part of the throat behind the nose). Most nasopharyngeal cancers are squamous cell carcinomas (cancer that begins in flat cells lining the nasopharynx).

The National Cancer Institute, part of the National Institutes of Health of the United States Department of Health and Human Services, is the Federal Government's principal agency for cancer research. The National Cancer Institute conducts, coordinates, and funds cancer research, training, health information dissemination, and other programs with respect to the cause, diagnosis, prevention, and treatment of cancer. Access the National Cancer Institute Web site at http://www.cancer.gov. Also called NCI.

A federal agency in the U.S. that conducts biomedical research in its own laboratories; supports the research of non-Federal scientists in universities, medical schools, hospitals, and research institutions throughout the country and abroad; helps in the training of research investigators; and fosters communication of medical information. Access the National Institutes of Health Web site at http://www.nih.gov. Also called NIH.

An addictive, poisonous chemical found in tobacco. It can also be made in the laboratory. When it enters the body, nicotine causes an increased heart rate and use of oxygen by the heart, and a sense of well-being and relaxation. It is also used as an insecticide.

A severe inflammation of the lungs in which the alveoli (tiny air sacs) are filled with fluid. This may cause a decrease in the amount of oxygen that blood can absorb from air breathed into the lung. Pneumonia is usually caused by infection but may also be caused by radiation therapy, allergy, or irritation of lung tissue by inhaled substances. It may involve part or all of the lungs.

Energy released in the form of particle or electromagnetic waves. Common sources of radiation include radon gas, cosmic rays from outer space, medical x-rays, and energy given off by a radioisotope (unstable form of a chemical element that releases radiation as it breaks down and becomes more stable).

The watery fluid in the mouth made by the salivary glands. Saliva moistens food to help digestion and it helps protect the mouth against infections.

In medicine, a loss of blood flow to part of the brain, which damages brain tissue. Strokes are caused by blood clots and broken blood vessels in the brain. Symptoms include dizziness, numbness, weakness on one side of the body, and problems with talking, writing, or understanding language. The risk of stroke is increased by high blood pressure, older age, smoking, diabetes, high cholesterol, heart disease, atherosclerosis (a build-up of fatty material and plaque inside the coronary arteries), and a family history of stroke.

The sudden and unexpected death of a healthy child who is younger than one year old, usually during sleep. The cause of sudden infant death syndrome is not known. Also called crib death and SIDS.

A plant with leaves that have high levels of the addictive chemical nicotine. The leaves may be smoked (in cigarettes, cigars, and pipes), applied to the gums (as dipping and chewing tobacco), or inhaled (as snuff). Tobacco leaves also contain many cancer-causing chemicals, and tobacco use and exposure to secondhand tobacco smoke have been linked to many types of cancer and other diseases. The scientific name is Nicotiana tabacum.

Having to do with poison or something harmful to the body. Toxic substances usually cause unwanted side effects.

Fluid containing water and waste products. Urine is made by the kidneys, stored in the bladder, and leaves the body through the urethra.

A substance used to make plastics. Exposure to vinyl chloride may increase the risk of developing liver, brain, and lung cancers; lymphoma; and leukemia.