What is the Definition of Passive Smoking?

What is Meant by the Term Passive Smoking?

woman holding a cigarette
What is meant by the term passive smoking?. Flickr.com/Creative Commons/John Benson

In recent years, the term "passive smoking" has been used in relation to medical conditions from cancer to heart disease. What does this mean, and what are the dangers?                 

Definition of Passive Smoking

Passive smoking refers to 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).

Types of Secondhand Smoke

  • 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 gases. 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.

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.

Diseases research has associated with passive smoking include:

  • Lung cancer - Of course 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 - 150,000 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 death syndrome - Young children exposed to secondhand smoke have a higher risk of sudden infant death syndrome.

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.

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. Check out these tips on how to protect yourself from secondhand smoke when traveling.


American Cancer Society. Secondhand Smoke. Updated 11/13/15. http://www.cancer.org/cancer/cancercauses/tobaccocancer/secondhand-smoke

National Cancer Institute. Secondhand Smoke and Cancer. Updated 01/02/11. http://www.cancer.gov/about-cancer/causes-prevention/risk/tobacco/second-hand-smoke-fact-sheet

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