Secondhand smoke is the smoke that comes from burning tobacco products, such as cigarettes and cigars, as well as the smoke exhaled by smokers. It contains thousands of harmful chemicals, many of which are toxic and can cause serious health problems. People who breathe in secondhand smoke can experience negative effects, even if they do not smoke themselves. Exposure to secondhand smoke is particularly dangerous for vulnerable groups, including children and pregnant women. It can lead to respiratory issues, heart disease, and an increased risk of lung cancer. Many places have implemented laws to restrict smoking in public areas to protect non-smokers from these harmful effects.