Inhalation of second-hand smoke causes premature death and a number of illnesses. It causes lung cancer, coronary heart disease, and respiratory diseases, and has a negative impact on conditions such as asthma. Staff in workplaces where people still smoke, such as in bars and restaurants in some countries, are heavily exposed to second-hand smoke. In the United Kingdom, inhalation of second-hand smoke is estimated to cause 14–15% of lung cancers in non-smokers. This fraction can be higher in countries where the prevalence of exposure to second-hand smoke is higher than in the United Kingdom, for example in countries with higher rates of smoking or higher prevalence of smoking in the home. Among persons who have never smoked (never-smokers), those exposed to second-hand smoke have twice the risk of lung cancer compared to those who are not exposed to second-hand smoke.

Smoking reduces fetal growth. Pregnant women who smoke cigarettes give birth to infants that weigh on average about 150–250 grams less than those of non-smokers. Low birth weight is associated with increased adverse health effects in the newborns. Smoking by the mother is also associated with an increased risk of sudden infant death syndrome (SIDS), and acute respiratory and ear problems in children.