Secondhand smoke, also known as passive smoke or environmental tobacco smoke, refers to the smoke that is exhaled by a smoker or given off by a burning cigarette, cigar, or pipe. This smoke contains a mixture of harmful chemicals and toxins that can be inhaled by non-smokers who are nearby. Secondhand smoke has been linked to numerous health risks, including respiratory infections, asthma exacerbation, lung cancer, and cardiovascular disease. Research in this area focuses on understanding the effects of secondhand smoke exposure on health, developing strategies to reduce exposure, and implementing policies to protect non-smokers from the dangers of secondhand smoke.