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Secondhand Smoke: Questions and Answers 

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. 

Key Points 

• Secondhand smoke (also called environmental tobacco smoke) is the 

combination of smoke given off by the burning end of a tobacco product 

and the smoke exhaled by the smoker (see Question 1). 

• Of the chemicals identified in secondhand smoke, more than 50 have been 

found to cause cancer (see Question 3). 

• Secondhand smoke causes lung cancer in nonsmokers (see Question 4). 

• Secondhand smoke causes heart disease in adults and sudden infant death 

syndrome (SIDS), ear infections, and asthma attacks in children (see 

Question 5). 

• There is no safe level of exposure to secondhand smoke (see Question 6). 
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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 
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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 
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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. 

# # # 
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Related NCI materials and Web pages: 

• National Cancer Institute Fact Sheet 10.16, Questions and Answers About 

Cigar Smoking and Cancer 

(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 

(http://www.cancer.gov/cancertopics/factsheet/Tobacco/cessation) 

• Smoking and Tobacco Control Monograph 10: Health Effects of Exposure to 

Environmental Tobacco Smoke 

(http://cancercontrol.cancer.gov/tcrb/monographs/10/index.html) 

• NCI's Smoking and Cancer Home Page 

(http://www.cancer.gov/cancertopics/smoking) 

For more help, contact: 

NCI’s Cancer Information Service 

Telephone (toll-free): 1–800–4–CANCER (1–800–422–6237) 

TTY (toll-free): 1–800–332–8615

LiveHelp® online chat: https://cissecure.nci.nih.gov/livehelp/welcome.asp

This fact sheet was reviewed on 8/1/07