Gender and the Pain Experience
Do men and women perceive and react to pain differently? Do men and women use different coping strategies when they experience recurrent or chronic pain? These questions are relevant to pain management providers when they assess and develop treatment plans for patients who experience pain on a daily basis.
Although once ignored in medical research, the idea that men and women experience pain differently is now accepted.1 In 1995, a major review of the research on gender and pain found that women experience more pain compared to men.2
The authors suggested that women have a lower pain threshold and tolerance to experimental pain including mechanical, thermal, and electrical stimuli. In other words, women experience painful stimuli as more intense than men.
However, the authors pointed out that there are a number of issues that contribute to the variability between the genders, including whether pain threshold or tolerance were being measured. In 2000, Dao and LeResche listed a number of factors that contribute to this variability, including dimensions of pain measured, type of stimulus, characteristics of the experimental environment, spatial and temporal aspects of the stimulus, and characteristics of the subject.3
I believe an additional factor must be controlled, and that is the sex of the observer. It is well understood that both men and women subjects react differently based on the gender of the experimenter.
Mechanisms Driving Differences
A well-designed study by Roger Fillingim et al showed that sex differences in pain response are well documented, but the mechanisms underlying these differences are not well understood.4 Fillingim proposed that gender roles and pain responses could be mediated by a subject’s perceived ability to tolerate pain. In other words, stereotypical sex roles are perceived to influence greater tolerance for pain among men than women. The results of this study showed that men had higher pain tolerance, but this triggered a higher blood pressure (BP) response. Fillingim et al pointed out that a body of evidence suggests that higher resting BP is associated with lower pain sensitivity.4 (see Interview with Roger B. Fillingim, PhD.)
One interesting explanation forwarded by the authors was that men tried harder to tolerate the pain, resulting in higher systolic BP. Also, keep in mind that systolic BP is related to sympathetic arousal. The authors concluded that perceived ability to tolerate pain may have influenced the relationship between cardiovascular variables and pain tolerance.2
Even though men appear to tolerate painful stimulus better, some data suggest that sustained low-level pain may be more disturbing to men than women. In a study by Frot et al, 10 men and 10 women received 2 applications of topical capsaicin for 30 minutes—first on the face and then the ankle. The subjects rated pain intensity, unpleasantness, and anxiety each minute during capsaicin application and for 30 minutes after its removal.
The investigators found that men showed a significant positive correlation between anxiety (sympathetic arousal) and pain intensity, whereas women did not.5 The results of the study support the general conclusion that although men perceive experimental pain less intensely than women do, they have more anxiety related to pain.
Evidence of the magnitude of gender differences in pain was revealed by a meta-analysis of research using experimentally induced pain.6 In this meta-analysis, Riley et al pointed out a number of assumptions relevant to gender differences, such as cultural and physiological influences, including the fact that males have been socialized to suppress outward signs of pain. They also mentioned the important influence of the menstrual cycle on pain perception. Females demonstrated more pain sensitivity following a mid-cycle surge during the luteal phase.7
An interesting study by Sarlani et al examined the concept of temporal summation as it relates to gender and pain.8 Temporal summation of pain is the increase in pain intensity after repetitive noxious stimulation of constant intensity. Temporal summation is regarded as a psycho-physiological correlate of wind-up. Wind-up is the increase in the magnitude of second-order nociceptive neuron responses to the application of repetitive noxious stimuli of constant strength. The authors believe that wind-up and temporal summation of pain share common features and have a central basis. Current thinking suggests that temporal summation is upregulated more frequently in women than in men.
Sarlani et al applied a series of repetitive, mildly noxious, mechanical stimuli to the fingers of 25 women and 25 men.8 The subjects rated the pain intensity and unpleasantness caused by the first, fifth, and tenth stimulus in the series, as well as after-sensations 15 seconds and 1 minute after the end of stimulation.
The investigators found that temporal summation of pain intensity and unpleasantness ratings were more pronounced in women than men (P<0.0001).8 Moreover, women reported higher ratings for the intensity and the unpleasantness of after-sensations (P<0.0005) and more frequent painful after-sensations (P<0.05).
“Greater temporal summation of pain and after sensations in women suggests that their central processing of nociceptive input may be more easily upregulated into pathological hyperexcitability, possibly accounting for the higher prevalence of various chronic pain conditions among women,” noted the authors.8
Most recently, Sorge et al discovered that female mice do not require microglia activation to produce mechanical pain hypersensitivity. Rather, the researchers wrote that “female mice achieved similar levels of pain hypersensitivity using adaptive immune cells, likely T lymphocytes. This sexual dimorphism suggests that male mice cannot be used as proxies for females in pain research.”9
Pain Medicine and Gender
The fact that men and women respond differently to pain medicine is an important issue in the practice of pain management. The most frequently prescribed pain medicines belong in the opioid class. Opioids work through specific opioid receptors that are well documented. Three types of opioid receptors have been identified: mu, delta, and kappa, with mu and kappa being the most frequently occurring receptors in humans.1
Research by Craft found that women use 40% less opioid-based medicine than men for postoperative pain.10 This finding was confirmed by Miaskowski et al in an analysis of 18 studies of postoperative opioid use. The researchers found an increase in opioid consumption among male patients in 10 studies (56%), but the remaining 8 studies (44%) showed no gender difference.11