Do men and women feel pain differently?

When it comes to coping with pain, women are the more voluble sex [source: Kritz]. Men, on the other hand, tend to bear their burdens quietly. Some researchers attribute that pattern to social conditioning; gender roles permit girls to cry and express their feelings more openly than boys, who are expected to keep a stiff upper lip.

But a study at the University of Florida debunks this social theory. Psychologists offered male and female participants a certain amount of money depending on how long they were able to hold their hands in an ice water bath. The researchers hypothesized that the monetary reward would eliminate any social gender norms, making both sexes equally motivated to hold their hands in the freezing water for as long as possible [source: Dye]. However, even with the cash incentive, the men still outlasted the women.

Psychologists also theorize that women's innate mindfulness might contribute to heightened pain sensitivity. In general, women are more attuned to how they feel physically, which might mentally predispose them to noticing pain. Females also have a higher incidence rate of anxiety and depression, which researchers have linked to greater pain sensitivity in women -- but not in men [source: Toomey].

Furthermore, research indicates that female bodies naturally respond to painful stimuli more intensely than males'. In one experiment, women's pupils dilated faster than men's when uncomfortable pressure was applied to their fingers. Since pupil dilation is a physiological response to pain that's controlled by the autonomic nervous system, the study demonstrated that the females' keener pain responses are beyond conscious control [source: Toomey]. And to top things off, fluctuating female hormones can either dampen or amplify pain on any given day.

For the women in the ice water study, research indicates that the time of the month could've impacted their pain tolerance. Although scientists haven't been able to quantify the precise effects of the menstrual cycle on pain, studies have drawn a correlation between estrogen and pain thresholds in women. Specifically, when estrogen levels crest, the female body responds more effectively to pain, releasing a greater amount of soothing endorphins and enkephalins [source: Dye]. This estrogen-pain connection could explain why postmenopausal women with low estrogen suffer more from chronic painful conditions, such as fibromyalgia [source: Kritz].

Due to the differences between how male and female bodies process pain, some scientists have started taking a gender-specific approach to formulating painkillers.

Not only do men and women feel pain differently, but medication that relieves men's pain won't necessarily work as well -- or at all, in some cases -- in women. Until 1993, the U.S. Food and Drug Administration (FDA) regulations excluded "women of childbearing age" from participating in clinical trial phases for new drugs, which meant that pharmaceutical companies often only tested on men [source: Toomey]. As a result, many painkiller formulations and dosages were developed based on the male body's pain response.

Morphine, one of the most commonly used painkillers, doesn't perform as effectively in both genders. For surgery patients undergoing general anesthesia, females require at least 30 percent more morphine than males [source: Toomey]. In addition, nalbuphine, which is often used to anesthetize women during childbirth, does little to mitigate pain in men [source: Economist].

Scientists attribute those gendered effects to variations in male and female brains. Both medications relieve pain by activating opioid receptors in the brain; opioid receptors counteract pain by blocking neurons from transmitting pain signals. Yet, morphine binds to a class of opioid receptors called mu receptors, and nalbuphine binds to kappa receptors. PET scans have shown, however, that mu receptors in healthy male and female brains activate through different pathways [source: Toomey]. Moreover, the male mu opioid system plays the starring role in pain relief, while the kappa system dominates in females.

Since drug testing was primarily focused on male pain responses in the past, the most popular painkillers were designed to stimulate mu opioids. As a result, chronic and severe pain in women has been harder to treat successfully. But now that scientists recognize that kappa receptor opioids better stifle pain in women, some are designing so-called "pink and blue painkillers" specifically tailored to males' and females' unique pain response systems [source: Economist]. If that becomes a medical reality, perhaps the gender pain gap will narrow in the future.