SEX-DIFFERENCES IN PAIN

Are there sex differences in pain? For experimentally delivered somati c stimuli, females have lower thresholds, greater ability to discrimin ate, higher pain ratings, and less tolerance of noxious stimuli than m ales. These differences, however, are small, exist only for certain fo rms of stimulation and are affected by many situational variables such as presence of disease, experimental setting, and even nutritive stat us. For endogenous pains, women report more multiple pains in more bod y regions than men. With no obvious underlying rationale, some painful diseases are more prevalent among females, others among males and, fo r many diseases, symptoms differ between females and males. Sex differ ences in attitudes exist that affect not only reporting, coping, and r esponses to treatment, but also measurement and treatment. So many var iables are operative, however, that the most striking feature of sex d ifferences in reported pain experience is the apparent overall lack of them. On the other hand, deduction from known biological sex differen ces suggests that these are powerful sex differences in the operation of pain mechanisms. First, the vaginal canal provides an additional ro ute in women for internal trauma and invasion by pathological agents t hat puts them at greater risk for developing hyperalgesia in multiple body regions. Second, sex differences in temporal patterns are likely to give rise to sex differences in how pain is ''learned'' and stimuli are interpreted, a situation that could lead to a greater variability and wider range of pains without obvious peripheral pathology among f emales. Third, sex differences in the actions of sex hormones suggest pain-relevant differences in the operation of many neuroactive agents, opiate and nonopiate systems, nerve growth factor, and the sympatheti c system. Thus, while inductive analysis of existing data demonstrate more similarities than differences in pain experience between females and males, deductive analysis suggests important operational sex diffe rences in its production.