experiencing highly stressful events in childhood (50). These are all potential points of intervention for cessation efforts and have the potential to reduce health costs associated with cigarette use. Cigarette use also varies by sex between countries, making it difficult to determine whether males or females are more likely to smoke (51). However, according to a review paper of 12 studies published between 1980 and 2010 assessing smoking initiation, boys had a lower age of smoking initiation relative to girls (52). Meanwhile, according to longitudinal studies, girls and boys have similar levels of overall substance use during early adolescence, but boys have greater increases in substance use during middle and late adolescence after initiation (53). Studies of adult smokers have also demonstrated that women tend to smoke fewer cigarettes per day, use cigarettes with lower nicotine content, and do not inhale as deeply as men. However, it remains uncertain whether this may be due to differences in sensitivity to nicotine or differences in other social factors associated with the experience of cigarette use (54).
