Health Risks of Secondhand Smoke

What is secondhand smoke?

Secondhand smoke (SHS) is also called environmental tobacco smoke (ETS). It’s a mixture of 2 forms of smoke that come from burning tobacco:

  • Mainstream smoke: The smoke exhaled by a smoker.
  • Sidestream smoke: Smoke from the lighted end of a cigarette, pipe, or cigar, or tobacco burning in a hookah. This type of smoke has higher concentrations of nicotine and cancer-causing agents (carcinogens) than mainstream smoke.

When non-smokers are exposed to SHS it’s called involuntary smoking or passive smoking. Non-smokers who breathe in SHS take in nicotine and toxic chemicals the same way people who smoke do. The more SHS you breathe, the higher the levels of these harmful chemicals in your body.

Why is secondhand smoke a problem?

Secondhand smoke (SHS) has the same harmful chemicals that smokers inhale. There’s no safe level of exposure for secondhand smoke (SHS).

Secondhand smoke causes cancer

Secondhand smoke is known to cause cancer. It has more than 7,000 chemicals, including at least 70 that can cause cancer.

SHS causes lung cancer, even in people who have never smoked. There’s also some evidence suggesting it might be linked in adults to cancers of the:

Exposure of mothers and babies to SHS is possibly linked to certain childhood cancers:

Secondhand smoke causes other diseases and death

Secondhand smoke can also be harmful in other ways. For instance, breathing secondhand smoke affects the heart and blood vessels, which increases the risk of having a heart attack. Exposure to secondhand smoke increases the risk of developing and dying from heart disease. It also increases the risk of having (and dying from) a stroke.

Secondhand smoke and your children’s health

Young children are most affected by SHS and least able to avoid it. Most of their exposure to SHS comes from adults (parents or others) smoking at home. Studies show that children whose parents smoke:

  • Get sick more often
  • Have more lung infections (like bronchitis and pneumonia)
  • Are more likely to cough, wheeze, and have shortness of breath
  • Get more ear infections

Secondhand smoke can also trigger asthma attacks or make asthma symptoms worse.

Some of these problems might seem small, but they can add up quickly. Think of the expenses, doctor visits, medicines, lost school time, and often lost work time for the parent who must stay home with a sick child. And this doesn’t include the discomforts that the child goes through.

In very young children, SHS also increases the risk for more serious problems, including sudden infant death syndrome (SIDS).

Where is secondhand smoke a problem?

You should be especially concerned about exposure to secondhand smoke (SHS) in these places:

At work

The workplace is a major source of SHS exposure for many adults.

The Occupational Safety and Health Administration (OSHA) and the National Institute for Occupational Safety and Health (NIOSH), federal agencies responsible for health and safety in the workplace, recognize there are no known safe levels of SHS and recommend that exposures be reduced to the lowest possible levels.

The Surgeon General has said that smoke-free workplace policies are the only way to prevent SHS exposure at work. Separating smokers from non-smokers, cleaning the air, and ventilating the building cannot prevent exposure if people still smoke inside the building. An extra bonus of workplace smoking restrictions, other than protecting non-smokers, is that they may also encourage people who do smoke to smoke less, or even quit.

In public places

Everyone can be exposed to SHS in public places where smoking is allowed, such as some restaurants, shopping centers, public transportation, parks, and schools. The Surgeon General has suggested people choose smoke-free restaurants and businesses, and let owners of businesses that are not smoke-free know that SHS is harmful to your family’s health.

Public places where children go are a special area of concern. Make sure that your children’s daycare centers and schools are smoke-free.

Some businesses might be afraid to ban smoking, but there’s no strong evidence that going smoke-free is bad for business.

At home

Making your home smoke-free may be one of the most important things you can do for the health of your family. Any family member can develop health problems related to SHS. Children’s growing bodies are especially sensitive to the toxins in SHS. And think about it: we spend more time at home than anywhere else. A smoke-free home protects your family, your guests, and even your pets.

Multi-unit housing where smoking is allowed is a special concern and a subject of research. Tobacco smoke can move through air ducts, wall and floor cracks, elevator shafts, and along crawl spaces to contaminate units on other floors, even those that are far from the smoke. SHS cannot be controlled with ventilation, air cleaning, or by separating smokers from non-smokers.

In the car

Americans spend a great deal of time in cars, and if someone smokes there, the toxins can build up quickly – even when the windows are open or the air-conditioner is on. Again, this can be especially harmful to children.

In response to this fact, many expert medical groups have been working to encourage people to make their cars, as well as their homes, smoke-free. Some states and cities even have laws that ban smoking in the car if carrying passengers under a certain age or weight. And many facilities such as city buildings, malls, schools, colleges, and hospitals ban smoking on their grounds, including their parking lots.

There is no safe level of exposure to secondhand smoke (SHS). Any exposure is harmful.

The only way to fully protect non-smokers from exposure to SHS indoors is to prohibit all smoking in that indoor space or building. Separating smokers from non-smokers, cleaning the air, and ventilating buildings cannot keep non-smokers from being exposed to SHS.

What can be done about secondhand smoke?

Many US local and state governments, and even federal governments in some other countries, have decided that protecting the health of employees and others in public places is of the utmost importance and have passed clean indoor air laws. Although the laws vary from place to place, they are becoming more common. Detailed information on smoking restrictions in each state is available from the American Lung Association.

You don’t have to wait for the government to act. Even if you smoke, you can decide to make your home and car smoke-free. This is the safest thing to do for your children, other family members, pets, and guests.

Are lingering smoking odors harmful?

There’s very little research so far on whether lingering tobacco smoke odors or residuals from it on surfaces can cause cancer in people. Research does show that particles from secondhand tobacco smoke can settle in dust and on surfaces and remain there long after the smoke is gone. Some studies suggest the particles can last for months. Even though it’s no longer in the form of smoke, researchers often call this thirdhand smoke (THS) or residual tobacco smoke.

Particles that settle out from tobacco smoke have been shown to combine with gases in the air to form cancer-causing compounds that settle onto surfaces. For instance, some of the carcinogens that are known to cause lung cancer have been found in dust samples taken from the homes of smokers. Research has also shown that thirdhand smoke can damage human DNA in cell cultures and might increase lung cancer risk in lab animals.

Though it’s not yet clear if such smoke residue can cause cancer, any effects would probably be small compared with direct exposure to SHS. Still, the compounds may be stirred up and inhaled with other house dust, and may also be accidentally taken in through the mouth. Because of this, any risk the compounds pose is probably greater for babies and children who play on the floor and often put things in their mouths.

The health risks of THS are an active area of research.

Is exposure to secondhand e-cigarette aerosol harmful?

As e-cigarettes and similar devices have become more popular in recent years, a growing concern is whether the aerosol of tiny particles exhaled by users, sometimes referred to as secondhand vapor, is harmful to other people who breathe it in.

Scientists are still learning about the health effects of being exposed to secondhand e-cigarette aerosol. However, the US Surgeon General has concluded that e-cigarette aerosol is not harmless. Secondhand aerosol can expose others to nicotine, and possibly to other harmful chemicals.

Smoke-free and tobacco-free policies already in place should also cover e-cigarettes. This will help non-users avoid being exposed to potentially harmful e-cigarette aerosol.

To learn more about e-cigarettes and similar devices, see What Do We Know About E-cigarettes?

The American Cancer Society medical and editorial content team

Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

Centers for Disease Control and Prevention. Health Effects of Secondhand Smoke. 2020. Accessed at https://www.cdc.gov/tobacco/data_statistics/fact_sheets/secondhand_smoke/health_effects/index.htm on October 14, 2020.

Centers for Disease Control and Prevention. Secondhand Smoke (SHS) Facts. 2018. Accessed at https://www.cdc.gov/tobacco/data_statistics/fact_sheets/secondhand_smoke/general_facts/index.htm on October 14, 2020.

Dreyfuss JH. Thirdhand smoke identified as potent, enduring carcinogen. CA Cancer J Clin. 2010;60(4):203-204.

Gentzke AS, Wang TW, Marynak KL, Trivers KF, King BA. Exposure to secondhand smoke and secondhand e-cigarette aerosol among middle and high school students. Prev Chronic Dis. 2019;16:180531. DOI: http://dx.doi.org/10.5888/pcd16.180531

Hang B, Sarker AH, Havel C, et al. Thirdhand smoke causes DNA damage in human cells. Mutagenesis. 2013;28(4):381-391.

Hang B, Wang Y, Huang Y, et al. Short-term early exposure to thirdhand cigarette smoke increases lung cancer incidence in mice. Clin Sci (Lond). 2018;132(4):475-488.

Hoh E, Hunt RN, Quintana PJ, et al. Environmental tobacco smoke as a source of polycyclic aromatic hydrocarbons in settled household dust. Environ Sci Technol. 2012;46(7):4174-4183.

International Agency for Research on Cancer. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 100E: Personal Habits and Indoor Combustions. Lyon, France: World Health Organization International Agency for Research on Cancer; 2012. 

Moon KA, Magid H, Torrey C, et al. Secondhand smoke in waterpipe tobacco venues in Istanbul, Moscow, and Cairo. Environ Res. 2015;142:568-574.

National Cancer Institute. Secondhand Smoke and Cancer. 2018. Accessed at https://www.cancer.gov/about-cancer/causes-prevention/risk/tobacco/second-hand-smoke-fact-sheet on October 14, 2020.

Raoof SA, Agaku IT, Vardavas CI. A systematic review of secondhand smoke exposure in a car: Attributable changes in atmospheric and biological markers. Chron Respir Dis. 2015;12(2):120-131.

Sleiman M, Gundel LA, Pankow JF, et al. Formation of carcinogens indoors by surface-mediated reactions of nicotine with nitrous acid, leading to potential thirdhand smoke hazards. Proc Natl Acad Sci USA. 2010;107(15):6576-6581.

Thomas JL, Hecht SS, Luo X, et al. Thirdhand tobacco smoke: A tobacco-specific lung carcinogen on surfaces in smokers' homes. Nicotine Tob Res. 2014;16(1):26-32.

US Department of Health and Human Services. E-cigarette Use Among Youth and Young Adults. A Report of the Surgeon General. Atlanta (GA): US Department of Health and Human Services, Centers for Disease Control and Prevention, National Center of Chronic Disease Prevention and Health Promotion, Office on Smoking and Health; 2016.

US Department of Health & Human Services. How Tobacco Smoke Causes Disease: The Biology and Behavioral Basis for Smoking-Attributable Disease: A Report of the Surgeon General. 2010. Accessed at https://www.ncbi.nlm.nih.gov/books/NBK53017/ on October 15, 2020.

US Department of Health and Human Services. The Health Consequences of Involuntary Exposure to Tobacco Smoke: A Report of the Surgeon General. 2006. Accessed at https://www.ncbi.nlm.nih.gov/books/NBK44324/ on October 14, 2020.

US Environmental Protection Agency. Secondhand Tobacco Smoke and Smoke-free Homes. 2020. Accessed at www2.epa.gov/indoor-air-quality-iaq/secondhand-tobacco-smoke-and-smoke-free-homes on October 15, 2020.

References

Centers for Disease Control and Prevention. Health Effects of Secondhand Smoke. 2020. Accessed at https://www.cdc.gov/tobacco/data_statistics/fact_sheets/secondhand_smoke/health_effects/index.htm on October 14, 2020.

Centers for Disease Control and Prevention. Secondhand Smoke (SHS) Facts. 2018. Accessed at https://www.cdc.gov/tobacco/data_statistics/fact_sheets/secondhand_smoke/general_facts/index.htm on October 14, 2020.

Dreyfuss JH. Thirdhand smoke identified as potent, enduring carcinogen. CA Cancer J Clin. 2010;60(4):203-204.

Gentzke AS, Wang TW, Marynak KL, Trivers KF, King BA. Exposure to secondhand smoke and secondhand e-cigarette aerosol among middle and high school students. Prev Chronic Dis. 2019;16:180531. DOI: http://dx.doi.org/10.5888/pcd16.180531

Hang B, Sarker AH, Havel C, et al. Thirdhand smoke causes DNA damage in human cells. Mutagenesis. 2013;28(4):381-391.

Hang B, Wang Y, Huang Y, et al. Short-term early exposure to thirdhand cigarette smoke increases lung cancer incidence in mice. Clin Sci (Lond). 2018;132(4):475-488.

Hoh E, Hunt RN, Quintana PJ, et al. Environmental tobacco smoke as a source of polycyclic aromatic hydrocarbons in settled household dust. Environ Sci Technol. 2012;46(7):4174-4183.

International Agency for Research on Cancer. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 100E: Personal Habits and Indoor Combustions. Lyon, France: World Health Organization International Agency for Research on Cancer; 2012. 

Moon KA, Magid H, Torrey C, et al. Secondhand smoke in waterpipe tobacco venues in Istanbul, Moscow, and Cairo. Environ Res. 2015;142:568-574.

National Cancer Institute. Secondhand Smoke and Cancer. 2018. Accessed at https://www.cancer.gov/about-cancer/causes-prevention/risk/tobacco/second-hand-smoke-fact-sheet on October 14, 2020.

Raoof SA, Agaku IT, Vardavas CI. A systematic review of secondhand smoke exposure in a car: Attributable changes in atmospheric and biological markers. Chron Respir Dis. 2015;12(2):120-131.

Sleiman M, Gundel LA, Pankow JF, et al. Formation of carcinogens indoors by surface-mediated reactions of nicotine with nitrous acid, leading to potential thirdhand smoke hazards. Proc Natl Acad Sci USA. 2010;107(15):6576-6581.

Thomas JL, Hecht SS, Luo X, et al. Thirdhand tobacco smoke: A tobacco-specific lung carcinogen on surfaces in smokers' homes. Nicotine Tob Res. 2014;16(1):26-32.

US Department of Health and Human Services. E-cigarette Use Among Youth and Young Adults. A Report of the Surgeon General. Atlanta (GA): US Department of Health and Human Services, Centers for Disease Control and Prevention, National Center of Chronic Disease Prevention and Health Promotion, Office on Smoking and Health; 2016.

US Department of Health & Human Services. How Tobacco Smoke Causes Disease: The Biology and Behavioral Basis for Smoking-Attributable Disease: A Report of the Surgeon General. 2010. Accessed at https://www.ncbi.nlm.nih.gov/books/NBK53017/ on October 15, 2020.

US Department of Health and Human Services. The Health Consequences of Involuntary Exposure to Tobacco Smoke: A Report of the Surgeon General. 2006. Accessed at https://www.ncbi.nlm.nih.gov/books/NBK44324/ on October 14, 2020.

US Environmental Protection Agency. Secondhand Tobacco Smoke and Smoke-free Homes. 2020. Accessed at www2.epa.gov/indoor-air-quality-iaq/secondhand-tobacco-smoke-and-smoke-free-homes on October 15, 2020.

Last Revised: October 28, 2020

What is secondhand smoke?

Secondhand smoke (SHS) is also called environmental tobacco smoke (ETS). It’s a mixture of 2 forms of smoke that come from burning tobacco:

  • Mainstream smoke: The smoke exhaled by a smoker.
  • Sidestream smoke: Smoke from the lighted end of a cigarette, pipe, or cigar, or tobacco burning in a hookah. This type of smoke has higher concentrations of nicotine and cancer-causing agents (carcinogens) than mainstream smoke.

When non-smokers are exposed to SHS it’s called involuntary smoking or passive smoking. Non-smokers who breathe in SHS take in nicotine and toxic chemicals the same way people who smoke do. The more SHS you breathe, the higher the levels of these harmful chemicals in your body.

Why is secondhand smoke a problem?

Secondhand smoke (SHS) has the same harmful chemicals that smokers inhale. There’s no safe level of exposure for secondhand smoke (SHS).

Secondhand smoke causes cancer

Secondhand smoke is known to cause cancer. It has more than 7,000 chemicals, including at least 70 that can cause cancer.

SHS causes lung cancer, even in people who have never smoked. There’s also some evidence suggesting it might be linked in adults to cancers of the:

Exposure of mothers and babies to SHS is possibly linked to certain childhood cancers:

Secondhand smoke causes other diseases and death

Secondhand smoke can also be harmful in other ways. For instance, breathing secondhand smoke affects the heart and blood vessels, which increases the risk of having a heart attack. Exposure to secondhand smoke increases the risk of developing and dying from heart disease. It also increases the risk of having (and dying from) a stroke.

Secondhand smoke and your children’s health

Young children are most affected by SHS and least able to avoid it. Most of their exposure to SHS comes from adults (parents or others) smoking at home. Studies show that children whose parents smoke:

  • Get sick more often
  • Have more lung infections (like bronchitis and pneumonia)
  • Are more likely to cough, wheeze, and have shortness of breath
  • Get more ear infections

Secondhand smoke can also trigger asthma attacks or make asthma symptoms worse.

Some of these problems might seem small, but they can add up quickly. Think of the expenses, doctor visits, medicines, lost school time, and often lost work time for the parent who must stay home with a sick child. And this doesn’t include the discomforts that the child goes through.

In very young children, SHS also increases the risk for more serious problems, including sudden infant death syndrome (SIDS).

Where is secondhand smoke a problem?

You should be especially concerned about exposure to secondhand smoke (SHS) in these places:

At work

The workplace is a major source of SHS exposure for many adults.

The Occupational Safety and Health Administration (OSHA) and the National Institute for Occupational Safety and Health (NIOSH), federal agencies responsible for health and safety in the workplace, recognize there are no known safe levels of SHS and recommend that exposures be reduced to the lowest possible levels.

The Surgeon General has said that smoke-free workplace policies are the only way to prevent SHS exposure at work. Separating smokers from non-smokers, cleaning the air, and ventilating the building cannot prevent exposure if people still smoke inside the building. An extra bonus of workplace smoking restrictions, other than protecting non-smokers, is that they may also encourage people who do smoke to smoke less, or even quit.

In public places

Everyone can be exposed to SHS in public places where smoking is allowed, such as some restaurants, shopping centers, public transportation, parks, and schools. The Surgeon General has suggested people choose smoke-free restaurants and businesses, and let owners of businesses that are not smoke-free know that SHS is harmful to your family’s health.

Public places where children go are a special area of concern. Make sure that your children’s daycare centers and schools are smoke-free.

Some businesses might be afraid to ban smoking, but there’s no strong evidence that going smoke-free is bad for business.

At home

Making your home smoke-free may be one of the most important things you can do for the health of your family. Any family member can develop health problems related to SHS. Children’s growing bodies are especially sensitive to the toxins in SHS. And think about it: we spend more time at home than anywhere else. A smoke-free home protects your family, your guests, and even your pets.

Multi-unit housing where smoking is allowed is a special concern and a subject of research. Tobacco smoke can move through air ducts, wall and floor cracks, elevator shafts, and along crawl spaces to contaminate units on other floors, even those that are far from the smoke. SHS cannot be controlled with ventilation, air cleaning, or by separating smokers from non-smokers.

In the car

Americans spend a great deal of time in cars, and if someone smokes there, the toxins can build up quickly – even when the windows are open or the air-conditioner is on. Again, this can be especially harmful to children.

In response to this fact, many expert medical groups have been working to encourage people to make their cars, as well as their homes, smoke-free. Some states and cities even have laws that ban smoking in the car if carrying passengers under a certain age or weight. And many facilities such as city buildings, malls, schools, colleges, and hospitals ban smoking on their grounds, including their parking lots.

There is no safe level of exposure to secondhand smoke (SHS). Any exposure is harmful.

The only way to fully protect non-smokers from exposure to SHS indoors is to prohibit all smoking in that indoor space or building. Separating smokers from non-smokers, cleaning the air, and ventilating buildings cannot keep non-smokers from being exposed to SHS.

What about lingering smoking odors?

There’s very little research so far on whether lingering tobacco smoke odors or residuals from it on surfaces can cause cancer in people. Research does show that particles from secondhand tobacco smoke can settle in dust and on surfaces and remain there long after the smoke is gone. Some studies suggest the particles can last for months. Even though it’s no longer in the form of smoke, researchers often call this thirdhand smoke (THS) or residual tobacco smoke.

Particles that settle out from tobacco smoke have been shown to combine with gases in the air to form cancer-causing compounds that settle onto surfaces. For instance, some of the carcinogens that are known to cause lung cancer have been found in dust samples taken from the homes of smokers. Research has also shown that thirdhand smoke can damage human DNA in cell cultures and might increase lung cancer risk in lab animals.

Though it’s not yet clear if such smoke residue can cause cancer, any effects would probably be small compared with direct exposure to SHS. Still, the compounds may be stirred up and inhaled with other house dust, and may also be accidentally taken in through the mouth. Because of this, any risk the compounds pose is probably greater for babies and children who play on the floor and often put things in their mouths.

No actual cancer risk has been measured at this time, but the health risks of THS are an active area of research.

What can be done about secondhand smoke?

Many US local and state governments, and even federal governments in some other countries, have decided that protecting the health of employees and others in public places is of the utmost importance and have passed clean indoor air laws. Although the laws vary from place to place, they are becoming more common. Detailed information on smoking restrictions in each state is available from the American Lung Association.

You don’t have to wait for the government to act. Even if you smoke, you can decide to make your home and car smoke-free. This is the safest thing to do for your children, other family members, pets, and guests.

Is exposure to secondhand e-cigarette aerosol harmful?

As e-cigarettes and similar devices have become more popular in recent years, a growing concern is whether the aerosol of tiny particles exhaled by users, sometimes referred to as secondhand vapor, is harmful to other people who breathe it in.

Scientists are still learning about the health effects of being exposed to secondhand e-cigarette aerosol. However, the US Surgeon General has concluded that e-cigarette aerosol is not harmless. Secondhand aerosol can expose others to nicotine, and possibly to other harmful chemicals.

Smoke-free and tobacco-free policies already in place should also cover e-cigarettes. This will help non-users avoid being exposed to potentially harmful e-cigarette aerosol.

To learn more about e-cigarettes and similar devices, see What Do We Know About E-cigarettes?

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