Final answer:
Secondhand smoke is a mixture of smoke from burning tobacco products and smoke exhaled by smokers. It can increase the risk of lung cancer and heart disease in non-smokers. Secondhand smoke contains thousands of harmful chemicals.
Step-by-step explanation:
Secondhand smoke is a mixture of the smoke given off by the burning of tobacco products, such as cigarettes, cigars or pipes, and the smoke exhaled by smokers. Non-smokers who are exposed to secondhand smoke may have an increased risk of lung cancer and heart disease.
Secondhand smoke contains over 7,000 harmful chemicals, including at least 250 that are known to damage human health. It can stay in the air for several hours after exposure.