During menses, pain thresholds have been found to be lower than during the rest of the menstrual cycle (Hurley & Adams, 2008). In the preovulatory or proliferative phase of the cycle, women have lower levels of progesterone and higher estradiol levels, indicating their pain thresholds are not different from men. Alternatively, during the relatively lower estradiol phase of the menstrual cycle after ovulation, females have higher pain scores to persistent noxious stimulation. This has been attributed to a reduction in endogenous opioid receptor activation in brain regions associated with analgesia when compared with a higher estradiol state. Age also modifies the pain threshold; advancing age is positively associated with a higher pain threshold.