Secondhand smoke

Synonyms: Passive smoke, Environmental tobacco smoke

Medical Specialties: Internal medicine, Oncology, Pulmonology

Clinical Definition

Secondhand smoke is the unintentional inhalation of smoke from a pipe, cigar or cigarette by nonsmokers. Secondhand smoke contains carcinogens and respiratory irritants, which over time can have consequences such as lung cancer and possibly COPD. The two forms of secondhand smoke include mainline smoke and sidestream smoke. Mainstream smoke is smoke exhaled. Sidestream smoke is the smoke from the burning end of a tobacco product. It contains higher levels of carcinogens than mainstream smoke.  

In Our Own Words

Tobacco smoke contains many chemicals that are considered irritants and cancer causing agents. Secondhand smoke occurs when a nonsmoker unintentionally breathes in the smoke from a pipe, cigarette or cigar. Continued exposure to secondhand smoke has proven to be a cause of lung diseases including lung cancer.


Secondhand smoke is divided into two different types. Breathing in smoke after a smoker exhales is called mainstream smoke. Inhaling smoke, which is from the burning end of a cigarette, is referred to as sidestream smoke. Over time either type of secondhand smoke can be harmful. But sidestream smoke is considered more dangerous because it contains higher levels of cancer causing chemicals. 

Relevant Conditions
  • Cancer
  • COPD
  • Heart disease
Common Types
  • Mainstream
  • Sidestream
Side Effects
  • Coughing
  • Wheezing
  • Ear infection in children
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