Current states of opinion and future directions on the epidemiology of sex differences in human pain.

One of the most commonly neglected findings in the human pain literature is the observation of sex differences in the mechanisms that support the phenotypic expression of pain. The present commentary describes an assessment of the prevalence of observed sex differences in various pain processes, and of how expert pain researchers interpret the epidemiology and, hence, the proximate and ultimate causes of such differences. Forty-two pain investigators completed an anonymous survey on the epidemiology of sex differences in the human pain experience. Investigator responses indicated that sex differences are pervasive across various areas of pain research, that sex differences are particularly pronounced in the area of situational influences on pain behaviors, and that contemporary pain researchers largely disagree on the epidemiology of, and hence, proximate and ultimate causes of the differences. The relevance of social situational factors on sex differences in pain behaviours is discussed in the context of evolutionary, developmental, social psychology and pain sensory systems that may function, in part, for regulating interpersonal intimacy.