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Secondhand Smoke

According to the 2014 Surgeon General’s Report, there have been more than 20 million smoking-related deaths in the United States since 1964; 2.5 million of those deaths were among non-smokers who died from exposure to secondhand smoke. During that same time, 100,000 babies have died due to parental smoking (including smoking during pregnancy).

What is secondhand smoke?

Secondhand smoke (SHS) is also known as environmental tobacco smoke (ETS). SHS is a mixture of 2 forms of smoke that come from burning tobacco:

  • Sidestream smoke: Smoke from the lighted end of a cigarette, pipe, or cigar
  • Mainstream smoke: The smoke exhaled by a smoker

Even though we think of these as the same, they aren’t. Sidestream smoke has higher concentrations of cancer-causing agents (carcinogens) and is more toxic than mainstream smoke. And, it has smaller particles than mainstream smoke. These smaller particles make their way into the lungs and the body’s cells more easily.

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 by the same route smokers do. The more SHS you breathe, the higher the level of these harmful chemicals in your body.

Why is secondhand smoke a problem?

Secondhand smoke causes cancer

Secondhand smoke is classified as a “known human carcinogen” (cancer-causing agent) by the US Environmental Protection Agency (EPA), the US National Toxicology Program, and the International Agency for Research on Cancer (IARC – a branch of the World Health Organization).

Tobacco smoke is a mixture of gases and particles. It contains more than 7,000 chemical compounds. More than 250 of these chemicals are known to be harmful, and at least 69 are known to cause cancer.

SHS has been linked to lung cancer. There is also some evidence suggesting it might be linked to lymphoma, leukemia, and brain tumors in children, and cancers of the larynx (voice box), pharynx (throat), nasal sinuses, brain, bladder, rectum, stomach, and breast in adults.

IARC reported in 2009 that parents who smoked before and during pregnancy were more likely to have a child with hepatoblastoma. This rare liver cancer is thought to start while the child is still in the uterus. Compared with non-smoking parents, the risk was about twice as high if only one parent smoked, but nearly 5 times higher when both parents smoked.

Secondhand smoke and breast cancer

Whether SHS increases the risk of breast cancer is still being studied. Both mainstream and sidestream smoke have chemicals that, in high concentrations, cause breast cancer in rodents. Chemicals from tobacco smoke reach breast tissue and can be found in breast milk.

One reason the link between SHS and breast cancer risk in human studies is uncertain is because breast cancer risk has not clearly been shown to be increased in active smokers. One possible explanation for this is that tobacco smoke might have different effects on breast cancer risk in smokers compared to those who are exposed to SHS.

A report from the California Environmental Protection Agency in 2005 concluded that the evidence regarding SHS and breast cancer is “consistent with a causal association” in younger women. This means SHS acts as if it could be a cause of breast cancer in these women. The 2014 US Surgeon General’s report concluded that there is “suggestive but not sufficient” evidence of a link at this point. In any case, this possible link to breast cancer is yet another reason to avoid secondhand smoke.

Secondhand smoke causes other diseases and death

Secondhand smoke can be harmful in many ways. Each year in the United States alone, it’s responsible for:

  • An estimated 42,000 deaths from heart disease in people who are current non-smokers
  • About 7,000 lung cancer deaths in non-smoking adults
  • Worse asthma and asthma-related problems in up to 1 million asthmatic children
  • Between 150,000 and 300,000 lower respiratory tract (lung and bronchus) infections in children under 18 months of age, with 7,500 to 15,000 hospitalizations each year
  • Making children much more likely to be put into intensive care when they have the flu; they stay in the hospital longer, and they’re more likely to need breathing tubes than kids who aren’t exposed to SHS

In the US, the costs of extra medical care, illness, and death caused by SHS are over $10 billion per year.

Some studies have linked SHS to mental and emotional changes, too. For instance, a Chinese study has suggested that SHS exposure is linked to an increased risk of severe dementia syndromes. A UK study reported that women exposed to SHS during pregnancy were at greater risk for symptoms of depression during the pregnancy. More research is needed to better understand the possible relationship between SHS, dementia, and mental health.

Surgeon General’s reports: Findings on smoking, secondhand smoke, and health

Since 1964, 32 tobacco-related US Surgeon General’s reports have been written to make the public aware of the health issues linked to tobacco and SHS. The ongoing research used in these reports still supports the fact that tobacco and SHS are linked to serious health problems that could be prevented. The reports have highlighted many important findings on SHS, such as:

  • SHS kills children and adults who don’t smoke.
  • SHS causes disease in children and in adults who don’t smoke.
  • Exposure to SHS while pregnant increases the chance that a woman will have a spontaneous abortion (miscarriage), stillborn birth, low birth-weight baby, and other pregnancy and delivery problems.
  • Babies and children exposed to SHS are at an increased risk of sudden infant death syndrome (SIDS), upper respiratory and lung infections, ear infections, and more severe and frequent asthma attacks.
  • Smoking by parents can cause wheezing, coughing, bronchitis, and pneumonia, and slow lung growth in their children.
  • SHS immediately affects the heart, blood vessels and circulation in a harmful way. Over time it can cause heart disease, strokes, and heart attacks.
  • SHS causes lung cancer in people who have never smoked. Even brief exposure can damage cells in ways that set the cancer process in motion. The Surgeon General estimates that living with a smoker increases the chance of getting lung cancer by 20% to 30%.
  • Chemicals in tobacco smoke damage sperm, which might reduce fertility and harm fetal development. SHS is known to damage sperm in animals, but more studies are needed to find out its effects on humans.
  • There is no safe level of exposure to SHS. Any exposure is harmful.
  • Millions of Americans, both children and adults, are still exposed to SHS in their homes and workplaces despite a great deal of progress in tobacco control. In fact, almost half of non-smokers and more that 60% of children in the US continue to be exposed.
  • On average, children are exposed to more SHS than non-smoking adults.
  • The only way to fully protect non-smokers from exposure to SHS indoors is to prevent 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.

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.

Occupational Safety and Health Administration (OSHA), the federal agency responsible for health and safety in the workplace, is concerned about SHS as a possible carcinogen at work. The National Institute for Occupational Safety and Health (NIOSH) and OSHA recognize there are no known safe levels of SHS, and recommend that exposures be reduced to the lowest possible levels.

Among adult non-smokers, SHS in the workplace has been linked to an increased risk for heart disease and lung cancer. 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, other than protecting non-smokers, is that workplace smoking restrictions may also encourage smokers to smoke less, or even quit.

In public places

Everyone can be exposed to SHS in public places, such as restaurants, shopping centers, public transportation, parks, schools, and daycare centers. The Surgeon General has suggested people choose restaurants and other businesses that are smoke-free, 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 center or school is smoke-free.

Some businesses seem to 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. Asthma, lung infections, and ear infections are more common in children who are around smokers. Some of these problems can become serious and even life-threatening. Others may seem like small problems, but they can add up quickly – the time for doctor visits, medicines, lost school time, and often lost work time for the parent who must stay home with a sick child are all costs that can impact a family.

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 apartments 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. Again, this can be especially harmful to children.

In response to this fact, the US Environmental Protection Agency has 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.

What about lingering smoking odors?

There’s no research in the medical literature as of yet showing that lingering cigarette odors cause cancer in people. Research does show that particles from secondhand tobacco smoke can settle into dust and onto 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, some researchers call this thirdhand smoke or residual tobacco smoke.

Tobacco smoke residue is still being studied. Particles that settle out from tobacco smoke can combine with gases in the air to form cancer-causing compounds that aren’t found in the fresh smoke. NNK and PAHs (polycyclic aromatic hydrocarbons), 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 the DNA of human cells in cell cultures.

Though yet unknown, the cancer-causing effects of smoke residue would likely 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 absorbed through the skin or accidentally taken in through the mouth. This is why any risk the compounds pose may be larger for babies and children who play on the floor and often put things in their mouths.

More recent research has shown that these compounds that settle into fabrics can be removed by normal washing.

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

What can be done about secondhand smoke?

Local, state, and federal authorities can enact public policies to protect people from secondhand smoke (SHS) and protect children from tobacco-related diseases and addiction. Because there are no safe levels of SHS, it’s important that any such policies be as strong as possible, and that they do not prevent action at other levels of government.

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. Many 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 makes breathing safer and more enjoyable for children, other family, and guests.

To learn more

More from your American Cancer Society

Here is more information you might find helpful. You also can order them free from our toll-free number, 1-800-227-2345, or read them on our website, www.cancer.org.

Questions About Smoking, Tobacco, and Health (also in Spanish)

Guide to Quitting Smoking (also in Spanish)

Smoking in the Workplace

Other organizations*

Along with the American Cancer Society, other sources of information and support include:

Environmental Protection Agency (EPA)
Phone number: 1-202-272-0167
Website: www.epa.gov/smokefree.

American Lung Association
Toll-free number: 1-800-586-4872
Website: www.lungusa.org

    Has printed quit materials, some in Spanish; also has details on state-specific tobacco/smoking control laws and policies at www.lungusa2.org/slati/.

Centers for Disease Control and Prevention
Office on Smoking and Health

Toll-free number: 1-800-232-4636 (1-800-CDC-INFO)
TTY: 1-888-232-6348
Website: www.cdc.gov/tobacco/basic_information/secondhand_smoke/index.htm
CDC main website: www.cdc.gov

    Offers answers to tobacco-related health questions, a lot of information on tobacco, smoking, and secondhand smoke, plus tools and resources for taking action against SHS

National Cancer Institute
Toll-free number: 1-800-422-6237 (1-800-4-CANCER)
TTY: 1-800-332-8615
Free tobacco line: 1-877-448-7848
Website: www.cancer.gov
Direct tobacco website: www.smokefree.gov

    Has quitting information, a cessation guide, and counseling via toll-free tobacco line as well as information on smoking by state and information about SHS

*Inclusion on this list does not imply endorsement by the American Cancer Society.

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.


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Last Medical Review: 12/22/2014
Last Revised: 03/05/2015