Secondhand smoke is a mix of the smoke from the burning ends of cigarettes, cigars, and pipes and the smoke exhaled by someone who is smoking. If you’re around someone who is smoking, you are at risk. Exposure greatly increases your chance of developing lung cancer and heart disease.
What's in Cigarette Smoke?
Secondhand Smoke and Asthma
U.S. Environmental Protection Agency (EPA) - Smoke-Free Homes