Health Risks of Secondhand Smoke

No amount of exposure is safe

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While much-deserved attention is focused on the health risks of smoking itself, secondhand smoke also leads to very serious health consequences, including respiratory conditions, heart disease, and cancer. You breathe in secondhand smoke, also known as environmental tobacco smoke (ETS), when you are exposed to pollutants in the air from tobacco products.

This is termed involuntary smoking or passive smoking—though you are not the one lighting up, you are exposed. There are no safe levels of secondhand smoke. It's important that you monitor your surroundings to protect your health.

Young child being exposed to secondhand smoke
ClarkandCompany / Getty Images

What's in Secondhand Smoke?

According to the Centers for Disease Control and Prevention (CDC), smoke emitted from tobacco contains about 7,000 toxic chemicals. Of these, hundreds are known toxins and approximately 70 are known to be linked to cancer (carcinogenic).

Chemicals such as benzene, formaldehyde, vinyl chloride, arsenic ammonia, hydrogen cyanide, and carbon monoxide are released into the air as a result of secondhand smoke. While smokers inhale these poisonous substances directly, nonsmokers nearby do so in an indirect manner due to the chemicals' presence in the air around them.

Secondhand smoke is a combination of two types of smoke. Both contain toxic chemicals, but there are some differences:

  • Mainstream smoke is what's exhaled from the person who is smoking. Inhaling it leads to the destruction of the cells that line your mouth, nose, and throat, which can cause sores, infections, and cancer.
  • Sidestream smoke is emitted from the end of a burning cigarette, cigar, pipe, or from tobacco burning in a hookah. This type of secondhand smoke causes damage to DNA (your body's genetic material) and inhibits DNA repair, predisposing to conditions such as cancer.

There are wide-ranging consequences of secondhand smoke beyond these. It isn't always clear which chemicals or which type of secondhand smoke is the root cause of each health effect—and experts suggest that secondhand smoke-associated health problems may be due to a combination of physiological responses.


Secondhand smoke is a respiratory irritant that can also affect the whole body. Once the chemicals are inhaled, they are absorbed into the bloodstream. The toxins may induce reactions that cause short-term issues (such as coughing and watery eyes) or long-term problems (such as heart disease).

Lung Concerns

Exposure to secondhand smoke can increase your risk of developing a lung infection due to the effects on your immune system and lungs.

And it can lead to chronic lung diseases like chronic obstructive pulmonary disease (COPD), asthma, allergies, chronic inflammation, pneumonia, bronchitis, and recurrent infections. This occurs because secondhand smoke causes mucous overproduction, impairment of the cilia lining the lungs, oxidative damage, injury to the cells lining the lungs, and immune cell reactivity.

Lung disease, including lung cancer, is the most common effect of secondhand smoke.


Secondhand smoke can also cause cancer in people who don't smoke. Declared by the United States Environmental Protection Agency (EPA) as a human lung carcinogen, secondhand smoke increases the risk of lung cancer by 20% to 30%.

The substances in secondhand smoke alter the environment of the lungs, resulting in DNA mutations, epigenetic changes (modified genetic expression), and immune dysfunction. All of these factors lead to lung cancer.

Non-small cell lung cancer is the most common type of cancer associated with secondhand smoke. People who already have lung cancer have a decreased response to lung cancer treatment and a shorter life expectancy when exposed to secondhand smoke.

According to the American Cancer Society, secondhand smoke can also result in other types of cancer, including:

  • Brain
  • Breast
  • Bladder
  • Larynx (voice box)
  • Pharynx (throat)
  • Rectum
  • Sinus
  • Stomach

Cardiovascular Disease

People who don't smoke have an increased risk of high blood pressure and cardiovascular disease when exposed to secondhand smoke, as it directly harms the blood vessels and heart tissue.

Chronic high blood pressure and recurrent blood vessel damage both result in atherosclerosis, also known as hardening of the arteries. With this condition, irregularities inside blood vessels can cause a build-up of debris and blood clots, eventually leading to heart attack and stroke.

Secondhand smoke can also increase the chances of having a heart attack after only relatively brief exposure.

Secondhand Smoke-Related Deaths

The American Lung Association estimates that secondhand smoke is responsible for more than 41,000 deaths each year—approximately 7,330 of which are from lung cancer and 33,950 of which are owed to heart disease.

High-Risk Groups

Although everyone exposed to secondhand smoke is at risk for related health effects, certain groups of people are at higher risk of developing severe problems from this exposure.

People with respiratory conditions, as well as teenagers, children, and babies in utero are more vulnerable to the harmful effects of secondhand smoke.

People With Respiratory Conditions

Secondhand smoke can worsen COPD and asthma. Adults with COPD often develop worsened symptoms, including increased shortness of breath, cough, wheezing, and mucus production.

Moreover, secondhand smoke acts as a major trigger for asthma attacks in adults and children who have the condition. In fact, sometimes the odor of smoke on clothing or skin alone can be enough to trigger asthma symptoms (this type of exposure is described as thirdhand smoke).


Babies developing in utero are exposed to toxins that can have an impact on their health if their mother smokes or is exposed to smoke from others. In both cases, this is considered secondhand smoke exposure for the fetus.

Babies born to mothers who smoked or who were exposed to secondhand smoke while pregnant are at increased risk of:

  • Strabismus (lazy eye)
  • Bone fractures
  • Asthma
  • Heart disease
  • Serious birth defects, such as cleft palate, heart defects, spinal cord defects, and kidney malformations

Pregnant mothers who smoke have a higher risk of miscarriage, premature birth, stillbirth, and neonatal death.

Children and Teens

According to the American Lung Association, more than 35% of American children (23 million) are exposed to secondhand smoke.

Children have smaller airways and ear canals and a developing immune system. These factors make young people especially sensitive to secondhand smoke. Generally, those who are exposed get sick more frequently than kids whose parents don't smoke.

In young babies, it increases the risk of sudden infant death syndrome (SIDS). In fact, each year, secondhand smoke is associated with 7,500 to 15,000 hospitalizations of infants and toddlers, and leads to more than 430 SIDS-related deaths.

When a child or teen is exposed to secondhand smoke, breathing becomes impaired as the airways become inflamed and filled with mucus. This increases susceptibility to symptoms such as coughing and wheezing. It is also a powerful trigger for children who have asthma (exposure aggravates asthma symptoms in more than 202,000 children annually) and contributes to tens of thousands of new cases each year in children.

Young people exposed to secondhand smoke are also more likely to experience frequent respiratory infections like pneumonia and bronchitis. And because secondhand smoke impairs the immune system, contagious infections can flourish, causing major illnesses including tuberculosis in at-risk children.

Secondhand smoke can also cause fluid buildup in the middle ear, making kids who are exposed more prone to ear infections, resulting in 790,000 doctor's office visits every year.

What About Vaping Smoke?

E-cigarette emissions are aerosols that can contain nicotine and highly toxic compounds called volatile organic compounds (VOCs), such as benzene, acetaldehyde, formaldehyde, as well as tobacco-specific nitrosamines. This, like cigarette smoke, is harmful—particularly to children and to adolescents' brain development, according to the U.S. Surgeon General.

Preventing Exposure

Preventing secondhand smoke exposure often involves establishing new rules and making changes to the places you frequent. Avoiding it entirely is the goal, but it's especially important that you aim to do so in indoor spaces such as homes, public buildings, offices, and cars.

If you have any type of respiratory condition, including asthma and COPD, it is critical that you not only quit smoking but avoid secondhand smoke as well.

Strategies for staying away from secondhand smoke include:

  • Never allow anyone to smoke inside your home, office, or car. Explain your “smoke-free home” policy to everyone who visits. People who really care about you will respect and support your house rules.
  • Advise guests and family members who can't abstain from smoking to smoke outside, away from open windows or doors.
  • Do not frequent places where people are smoking. If you must be in an area where public smoking is taking place, sit or stand in a well-ventilated, non-smoking section.
  • If family members smoke, suggest that they quit.

If your friend or loved one is having difficulty quitting, encourage them to talk to their healthcare team about getting help. Nicotine replacement therapy and other medications are available, and they can increase the chances of quitting for good.

While Traveling

Although many cities and communities have made great strides in banning smoking from public buildings, restaurants, and parks, there are still parts of the world where smoking is allowed everywhere. The best way to prevent exposure to secondhand smoke while traveling is to plan ahead and to advocate for yourself.

  • Request a non-smoking room: Whether you are booking a hotel room or a cabin on a cruise ship, always request a non-smoking room; never assume that's a given.
  • Plan ahead: Make your sensitivity to cigarette smoke known at the time of your reservation and at check-in. The hotel or ship’s cleaning crew can use a high-powered air filter system to clean the air in your room prior to your arrival if smoking has previously been allowed in the space.
  • Use a smoke filter mask: If you can’t avoid secondhand smoke in public places, avoid breathing it in by covering your mouth in smoky areas. A filter mask can block some air particles and is a handy and lightweight way to prevent exposure.
  • Aim to keep smoke off your clothing: If you can’t stay in a smoke-free hotel, keep your clothes stored in a garment bag or suitcase to keep them from absorbing cigarette smoke. If the dresser in the hotel smells of cigarette smoke, it's best that you don't use it. If you spend time in smoke-filled areas, store your dirty clothes in a separate bag away from the rest of your attire.

A Word From Verywell

Secondhand smoke is hard to avoid because it is caused by the actions of others. But the consequences of inhaling secondhand smoke, especially chronically, are pretty serious. Take control of your own exposure, even if you need to make some adjustments like wearing a mask or avoiding certain smoke contaminated places.

14 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading

By Deborah Leader, RN
 Deborah Leader RN, PHN, is a registered nurse and medical writer who focuses on COPD.