Level 1: What is second-hand smoke? Secondhand smoke, also known as environmental tobacco smoke, refers to the process in which harmful substances released in tobacco smoke inhaled by smokers stay in the air and are inhaled by others. Secondhand smoke contains more than 70 carcinogens, including nicotine, carbon monoxide, benzene and polycyclic aromatic hydrocarbons. Level 2: What are the dangers of second-hand smoke for pregnant women? Secondhand smoke inhaled by pregnant women can cause great harm to the fetus. First of all, second-hand smoke inhaled by pregnant women contains substances such as nicotine and carbon monoxide, which can enter the fetus through the blood. Nicotine affects fetal brain development, causing