Health Effects of Secondhand Smoke and Thirdhand Smoke

Almost everyone these days knows that smoking tobacco is not healthy. What many people may not realize is that exposure to tobacco through secondhand smoke can have some of the same health risks as active smoking. Even thirdhand exposure may have negative health consequences. 

Here, we’ll go over what secondhand and thirdhand smoking are and their risks to your health. We’ll also cover what you can do to protect yourself and your family.

What is secondhand smoke?

Secondhand smoke (SHS) is exposure to tobacco smoke in your environment. It is also known as environmental tobacco smoke (ETS). Secondhand smoke is a combination of two types of smoke, mainstream smoke and sidestream smoke:

• Mainstream smoke: This is the smoke that a person who is actively smoking exhales.

• Sidestream smoke: This is smoke from the lighted end of a cigarette, cigar, pipe, or hookah tobacco. Sidestream smoke may actually be more dangerous because it has higher levels of nicotine and cancer-causing chemicals.

There is no safe level of exposure for secondhand smoke. Even a small exposure for a short time can be harmful to your health. 

Where are you exposed to secondhand smoke?

There are many places where you can be exposed to secondhand smoke:

• At home: Some people live with a person who smokes and are exposed to secondhand smoke at home. This is often the case for children. 

• At work: Some people may have a co-worker who smokes. 

• In public: You may come across smokers in public areas like stores, shopping malls, bars, or restaurants. 

• On public transportation: This can also be a common place of exposure to secondhand smoke. 

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What health risks are associated with secondhand smoke?

Secondhand smoke can be very dangerous. When you inhale secondhand smoke, you inhale nicotine and other chemicals in cigarettes, just like people who actively smoke do. Secondhand smoke can contain up to 7,000 chemicals, many of which are toxic. Seventy of these chemicals are known to increase the risk of cancer.

Diseases associated with secondhand smoke

Secondhand smoke can cause many medical problems and long-term health consequences. Examples of these problems include heart disease, stroke, and lung cancer. Every year in the United States, secondhand smoke is responsible for over 7,300 deaths from lung cancer and 33,900 deaths from heart disease. That’s over 40,000 deaths a year from secondhand smoke. Worldwide, secondhand smoke causes nearly 1.2 million early deaths each year.

Who is at risk of harm from secondhand smoke?

Anyone who is exposed to secondhand smoke is at risk of health harm. Both adults and children, and even pets, may be affected. In the U.S., 25% of adults and 40% of children are exposed to secondhand smoke regularly. For children, that number is almost double for Black children (70%).

People who work in bars and restaurants or casinos may have significantly more exposure than those in other occupations or even those who have a smoker in their home. 

Adults and secondhand smoke

For adults, exposure to secondhand smoke can cause nose and eye irritation. It can have immediate effects on the heart and blood vessels. Secondhand smoke can also increase the risk of: 

• Stroke

• Heart disease

• Lung cancer

• Cancers of the nose, mouth, or throat

Nonsmokers who are exposed to secondhand smoke may have a 20% to 30% higher risk of developing heart disease and stroke. Pregnant women who smoke or are exposed to secondhand smoke have higher risks of miscarriage, premature birth, and low birth weight.

Infants and children and secondhand smoke

Exposure to smoke for infants and children as early as during fetal development can cause lifelong effects. Exposure to smoke in the womb or shortly after birth may lead to: 

• Poor lung development

• Sudden infant death syndrome (SIDS)

• Development of attention-deficit hyperactivity disorder (ADHD) or learning disabilities

Infants and children exposed to tobacco smoke are also more likely to have more frequent conditions than babies not exposed to smoke, such as: 

• Upper respiratory infections

• Bronchitis

• Pneumonia

• Ear infections

Exposure to smoke can also cause asthma attacks in children with asthma. Later in life, children exposed to secondhand smoke may be more likely to smoke themselves and are at higher risk of heart disease, lung cancer, and cataracts. 

Pets and secondhand smoke

Many people know that secondhand smoke is harmful to people. But many may not know that it can also affect pets. Living in a home with tobacco smoke can be dangerous for dogs, cats, and birds. Dogs exposed to secondhand smoke are at risk of nasal and lung cancer. Cats who live in a home with tobacco smoke may develop lung cancer and lymphoma. Cats exposed to tobacco smoke are also at a 2 to 4 times higher risk of mouth tumors. This is because cats they lick their fur to clean themselves, and in a smoky home their fur can contain toxins from the smoke in the air. Birds are sensitive to tobacco smoke in the environment and may develop pneumonia and lung cancer, as well as problems with their hearts, eyes, and skin, in addition to fertility issues.

Smaller animals, like fish or guinea pigs, can also be affected by secondhand smoke.

What is thirdhand smoke and who is at risk?

Thirdhand smoke is exposure to air and surfaces that have mixed with tobacco smoke. It can be found in carpets and on walls and furniture. Other surfaces where thirdhand smoke can be found are leather, books, and toys. Hair can be another source of it, too.

When household air and surfaces are exposed to tobacco smoke, they can absorb the smoke and form other chemicals that may have negative health effects. In the air, nicotine can combine with other common air pollutants to form dangerous substances. 

Research has shown that the formation of some of these substances increases over time. This means that the longer secondhand smoke interacts with the environment, the more toxic it may become. Later on, interaction or disruption of these surfaces can release these substances. The toxins can get into your body through your lungs, your skin, or your mouth, as is especially the case with young children. There is even some concern that chemicals may last on surfaces for weeks to months. 

Health risks of thirdhand smoke

The specific health effects of thirdhand smoke exposure are currently more difficult to define than for secondhand smoke. But, just as with secondhand smoke, anyone exposed is at risk. Research has shown that exposure to thirdhand smoke can damage DNA, which can increase the risk of cancer. Studies of children exposed to thirdhand smoke have shown: 

• There is evidence of nicotine on their skin and in their urine.

• Young children seem to have the greatest exposure to thirdhand smoke.

• This exposure may increase a child’s risk of cancer. 

Some people open windows, use fans or air conditioning, or choose to only smoke outside as a means of preventing thirdhand smoke inside the home. While these efforts may seem logical, none of these options completely prevents the formation of thirdhand smoke. The risk to others may be slightly reduced, but it is not eliminated by smoking outside. 

How to identify areas where thirdhand smoke is present

It can be difficult to know where thirdhand smoke is present, but there are a few ways you may be able to tell:

• Discolored surfaces: Frequent smoking inside a home, building, or car can lead to discoloration of surfaces and a distinct stale tobacco smell. 

• Stale tobacco smells: Smelling stale tobacco can be a strong warning sign. The smell comes from the release of chemicals from household surfaces exposed to tobacco smoke.

Thirdhand smoke can also be present without any smell at all. Being in a home or building where someone previously smoked can put you at risk of thirdhand smoke exposure. Using or renting a car that a smoker previously drove can also increase your risk. If you can’t tell by discoloration or smell, then the best thing to do is ask about whether smoking is or has been allowed in the home, building, or car. You can also ask about specific smoking policies and how the home or car is cleaned after smoking. 

Is the vapor from e-cigarettes as dangerous as secondhand and thirdhand smoke from regular cigarettes?

The vapor that comes from e-cigarettes may contain harmful chemicals, just like tobacco smoke. Some of these chemicals are known to cause serious lung problems, known as e-cigarette or vaping-associated lung injury (EVALI). Several serious cases of EVALI were identified in 2019, and as of 2020, there have been over 2,800 cases and 68 deaths in the U.S.

Less is known about the long-term effects and secondhand exposure of vaping compared to smoking tobacco. However, scientists do know that vaping releases chemicals that may cause problems in various body systems. The FDA does not currently regulate e-cigarettes. This makes it hard to know what ingredients they contain and what their possible health risks may be. Although the specific risks are hard to define, the U.S. Surgeon General has described e-cigarettes and vaping as “not harmless.” 

What can I do to decrease my health risks from second and third hand smoke?

There are a few things that you can do to decrease the health risks to you and your loved ones from secondhand and thirdhand smoke: 

• Quit smoking: First, if you smoke, try to quit. While cutting back or trying to quit, commit to making your home and car smoke-free. 

• Encourage others to quit: If you don’t smoke but are around smokers at home, encourage them to quit. Teach them about the risks of secondhand and thirdhand smoke and how these risks can affect everyone in the household. This is the best thing you can do for the health of everyone in your home.

• Push for a smoke-free policy at work: Many organizations have smoke-free policies in place that can help make the workplace a safe environment. Not all jobs have policies regarding smoking, but having a smoke-free policy is really the only way to avoid the risks of secondhand and thirdhand smoke at work. If your job does not have a smoke-free policy, talk to your employer and co-workers about the risks. Encouraging them to create a smoke-free policy can make a big difference for everyone in your workplace. 

• Choose smoke-free businesses and schools: When you are out and about, choose stores, restaurants, and shopping malls that have smoke-free policies. When planning childcare, choose daycares that are smoke-free and babysitters who don’t smoke. Talk to your older children about the risks of secondhand and thirdhand smoke exposure and encourage their schools to become tobacco-free. 

All of these efforts may seem like small things, but each one can help decrease the amount of secondhand or thirdhand smoke exposure. The more you can avoid secondhand and thirdhand smoke exposure, the better for you and your loved ones.

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Written by:

Kelly Elterman, MD

Kelly Elterman, MD, is a board-certified anesthesiologist by the American Board of Anesthesiologyand has been practicing clinically since she finished her residency training in 2013. Along with her training, she has over 10 years experience in anesthesiology.

Reviewed by:

Katie E. Golden, MD

Katie E. Golden, MD, is a board-certified emergency medicine physician and a medical editor at GoodRx.

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