Passive Smoking: Definition and Dangers

woman holding a cigarette Commons/John Benson

In recent years, the term "passive smoking" has been used in relation to medical conditions from cancer to heart disease. Passive smoking is defined as the involuntary inhalation of smoke from cigarettes (also cigars, hookah, marijuana, and even e-cigarettes) smoked by other people. In other words, passive smoking means breathing in secondhand smoke, or what is commonly referred to as environmental tobacco smoke (ETS). Learn about the dangers of passive smoking and how to reduce your exposure.

Types of Secondhand Smoke

There are two different types of secondhand smoke. While these have been grouped together in the past, they may affect people who are exposed in different ways. In addition, you may be more likely to be exposed to one type than the other depending on the setting.

  • Mainstream smoke (MSM): The term mainstream smoke refers to the smoke exhaled by a smoker.
  • Sidestream smoke (SSM): The term sidestream smoke refers to the smoke that is released from the end of a cigarette, cigar, pipe, hookah pipe, or joint, and accounts for roughly 85 percent of secondhand smoke exposure. SSM can be a greater danger than MSM not only in that it contains greater amounts of cancer-causing substances and toxins, but because it persists for a longer period of time—often lasting even after a cigarette has been extinguished.

Exposure to both forms of secondhand smoke can be affected by several variables including heat and humidity, the ventilation of a room, car or other space, and of course, how many smokers are present.

Thirdhand Smoke

Thirdhand smoke, the gases, and particles left over after a cigarette or another form of tobacco is extinguished, may also be inhaled via passive smoking. Through a process called "off-gassing," substances that have been deposited on surfaces as a result of smoking are released back into the air as gasses. Though this is likely a minor portion of the secondhand smoke inhaled as a result of passive smoking, thirdhand smoke can remain a problem for a long period of time after smoking has occurred.

Thirdhand smoke is of particular danger to young children who may be crawling around on the surfaces where thirdhand smoke accumulates. In addition, children are more likely to ingest these particles than adults.

Dangers of Passive Smoking

Just as smokers are exposed to known carcinogens (cancer-causing substances) and other toxic substances, passive smokers are exposed as well. Secondhand smoke is now considered a class A (the worst) carcinogen.

Passive smoking has been associated with a number of diseases. Some of these include:

Lung Cancer

Certainly, lung cancer is the first consequence of passive smoking that most people may think of, but the concerns don’t stop here. 7,000 die from lung cancer as a result of secondhand smoke exposure each year and living with someone who smokes increases the risk of developing lung cancer by 20 to 30 percent.

Other Cancers

Cancers such as head and neck cancers, bladder cancer, and others are elevated in passive smokers as well as active smokers.

Heart disease and Strokes 

Secondhand smoke is thought to cause 42,000 deaths from heart disease in non-smokers in the United States alone each year.

Lung Disease

Lung diseases such as asthma and chronic obstructive pulmonary disease are increased among non-smokers exposed to secondhand smoke.

Lung Infections

Roughly 50,000 to 300,000 cases of lower respiratory infections such as pneumonia occur each year in the U.S. in children under 18 months due to secondhand smoke. Children who live with a smoker and develop these infections are also more likely to need intensive care and ventilator support.

Sudden Infant Death Syndrome

Young children exposed to secondhand smoke have a higher risk of sudden infant death syndrome.

Pregnancy Complications

Passive smoking (exposure to secondhand smoke) while pregnant increases the risk of miscarriage, stillbirth, and low-birth-weight babies.

Passive Smoking Can be Additive

Just as smoking and other risk factors can be additive, or worse (the combination of smoking plus asbestos is riskier than would be expected from just adding the health risks of the two alone), the combination of passive smoking and other risk factors greatly increased the risk of illness. Passive smoking can also be additive with exposure to radon, and radon is currently the second greatest risk factor for lung cancer in the U.S. and the number one risk factor in non-smokers.

Preventing Passive Smoking

What can you do to avoid passive smoking, in other words, protect yourself from secondhand smoke exposure?

  • Do not allow others to smoke in your home or in your car.
  • Many public places in the United States are now smoke-free, but this isn't always the case when you travel abroad. Avoid establishments that allow smoking indoors or out-of-doors.

A Word From Verywell

It's much easier than in the past to avoid "passive smoking" although there are a number of situations in which people could still be at risk. There are no laws that prevent smoking in homes or cars, places where children as adults are often present. Though you may not always be popular for your choice, choose to always refuse to allow yourself to be a passive smoker.

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