Differential exposure or reactivity to postnatal environmental factors between males and females could also contribute to sex differences in mental disorders across the lifespan. With respect to other body systems, data suggest that females may suffer from more detrimental effects of smoking (eg, developing chronic obstructive pulmonary disease, COPD), 23 and alcohol misuse 37 than do males. More recently, sex differences in the microbiome have been proposed to protect males against autoimmune disorders. 38 Differential susceptibility to environmental exposures across the lifetime should also be considered in examining causes of sex differences in psychiatric disorders. For example, women are twice as likely as men to experience posttraumatic stress disorder (PTSD), even though men and women are exposed to traumatic events at approximately equal rates. However, the type of traumatic event varies by sex; women are more likely to experience intimate partner violence, sexual assault and childhood maltreatment, while men are more likely to have experienced accidental injury, nonsexual physical assault and war‐related events. 39
