What Is Secondhand Smoke?

Secondhand smoke comes from both the smoke that smokers exhale (called mainstream smoke) and the smoke floating from the end of the cigarette, cigar, or pipe (called sidestream smoke).


It may seem pretty harmless, but secondhand smoke actually contains thousands of chemicals — from arsenic and ammonia to hydrogen cyanide — many of which have been proven to be toxic or to cause cancer (called carcinogens). High concentrations of many of these chemicals are found in secondhand smoke. In fact, secondhand smoke significantly increases a person's risk for:


respiratory infections (like bronchitis and pneumonia)
asthma (secondhand smoke is a risk factor for the development of asthma and can trigger attacks in those who already have it)

coughing, sore throats, sniffling, and sneezing
cancer
heart disease
So secondhand smoke doesn't just impact a person in the future. It can cause problems right now, like affecting someone's sports performance or ability to be physically active.