Research is showing that there may be sex-related differences in the perception and response to pain between men and women. How much of a difference and why there is one remains a subject of controversy.
For many there is a belief that women have a higher pain threshold than men and are thus able to tolerate more pain. Some of this may come from the thought that the experience of childbirth makes women someone better able to tolerate pain. Research is suggesting otherwise.
“The question I get asked most often is how do people experience pain,” says Jeffrey Mogil, PhD, E.P. Taylor Professor of Pain Studies at McGill University in Montreal. “No one can really answer that since pain is a completely subjective experience. Not only can I not know if women experience pain differently, I can’t know if you experience pain differently from how I do.”
There are ways to measure whether one group is more sensitive to pain or has a lower tolerance. People are asked when they first feel the pain of a prick or other stimulus. There are widely used scales that rate pain and its intensity and when the pain is such that they can’t take it any more.
“When you bring men and men into the laboratory and you induce pain in a controlled manner, women report more pain than men,” says Roger B. Fillingim, PhD, director of the University of Florida Pain Research and Intervention Center of Excellence in Gainesville. “This is measured by threshold (how much stimulation before you first feel pain), tolerance (how much stimulation you are willing to take) and rating of a specific level of pain. It is remarkably consistent across many studies that women feel more pain than men.”
These results are from laboratory-induced pain. Whether this translates into differences in clinical pain has been much harder to sort out.
Women at greater risk for pain-related conditions
One thing that is certain in the general population, women are at greater risk for pain-related conditions men. There are more women than men reporting back pain, migraine and other headaches, fibromyalgia, lupus and various forms of arthritis. Then there are sex-specific syndromes such as premenstrual pain. Women in pain are more likely to seek out a health-care provider.
Generally, women are more likely to have more depression and anxiety. Women are also more likely show catastrophizing behaviors such as magnifying and focusing on the pain symptoms as well as feelings of hopelessness. All are known to increase the risk for pain.
Pain is an important part of survival. In our body and brain we have systems that modulate the pain signal. They either amplify or inhibit that input. A balance between amplification and inhibition allows you to feel an appropriate amount of pain, whatever that may be. When you have a balance in this pain modulation pathway, you can feel the pain you need for survival and control the pain you don’t. It is possible that various psychological and factors influencing this can differ between men and women.
Reasons not well understood
The reasons for these differences are not yet well understood. However, there are some biological differences that are intriguing lines of research.
There are hormonal differences that might explain some of the variation. Although mainly in laboratory animals, some studies suggest that the male hormone testosterone may protect against pain.
Animal studies have also suggested that there may be structural differences in the brain itself. Male mice and rats use a cell in the spinal cord called microglia to process pain. Female mice use a completely different cell called a T-cell. Despite the different pathways, the effects are same in both males and females.
“It hasn’t yet been tested in humans because there are no compounds currently on the market that target either the microglia or the T-cells,” says Dr. Mogil. “There have been clinical trials of promising pain medications that have failed to show an effect. They might have failed because their usefulness in only one gender may not have been measured by the way the study was structured.”
As far back as 2003, studies using radioactively tagged glucose in positron emission tomography showed there were variations in the areas of the brain that are more active during painful stimulus. The female brains were more involved in the limbic regions that are emotion-based centers. In men, the cognitive regions, or analytical centers, showed greater activity.
Societal roles can enter into the pain equation as well. Pain is not just a biological experience, and may not even be primarily biologic in nature.
“While people look at pain as being nerve centered, the actual perception goes on in the brain with all of the extra things that brings along with it,” says Dr. Fillingim. “Under normal circumstances, there is input from the body, but what the brains does with that information is critical in how much pain we actually experience.”
There have been many studies on social roles and gender differences. In general, higher levels of masculinity on well-documented scales are correlated with lower reports of pain in both genders. However, femininity is less consistently correlated to increased levels of pain.
“The question that we are still sorting through is whether highly masculine men report less pain because they think that is what masculine men are supposed to do,” says Dr. Fillingim. “Or are they reporting less pain because their masculinity includes other things that translate to lower perception? While social roles are definitely related to pain, what we don’t know yet is how much of that is an effect on reporting and how much is difference in the actual experience of pain which may have a biological basis.”
Limited help in making real-life decisions
While all of this research is interesting, they are limited in their ability to be used in making real-life decisions. Most of these are surveys and there have been no studies that look at the same people over decades to see changes over time.
“One of my greatest frustrations is that while we have learned a lot about sex differences in pain, we haven’t learned anything that we can to the clinic and apply to an individual person,” says Dr. Fillingim. “We can’t yet say that treatment A will work better in women and most males should be given treatment B. While who has more pain is valuable from a public health standpoint, the why is the more interesting clinical question.”
Society also may have an impact on treatment. Studies show that women’s pain reports are given less credence than those of men. Socrates used the term “hysteria,” from the Greek word for womb, to describe women’s complaints as coming from weakness, inferiority or being irrational.
Undertreatment of women
Despite evidence that women have more painful conditions than men, a long line of research says that women are more often undertreated for their pain. This under treatment has been shown to occur even when the practitioner is female. Women are more likely to be given the wrong diagnosis, told they are depressed and prescribed an antidepressant, or even sent home and told to rest.
“This tendency to devalue women’s symptoms derives in part from historical cultural influences, remnants of societal periods when male dominance and female subservience dictated that women’s voices were less important and thus not taken seriously, says Dr. Fillingim. “However, that women’s pain continues to be underappreciated also owes to the fact that much of our scientific knowledge of pain and related symptoms comes from studies of males. Therefore, when female pain experiences differ from those of males, they do not fit into our flawed understanding.”
Life-threatening sex difference in pain
One area where there is good research showing major differences in the presentation and intensity of pain can also be life threatening if misdiagnosed. Women’s pain from an acute heart attack is not like that seen in men.
Up to 15 percent of women do not experience the crushing chest pain radiating down the arm that men describe. Women tend to complain of being nauseous, sweat profusely and if they do have pain, it is in the tummy, under the rib cage and in the back or neck. It is often missed by those who don’t know the differences in how pain is experienced. It is an extremely important thing that women should know about.
Biology sex specific
The takeaway is that the question everyone is asking isn’t the one that is interesting.
“The fact that women are more sensitive to pain is true,” says Dr. Mogil. “The important message is that regardless of differences in sensitivity, the biology behind pain is amazingly sex-specific. There is no obvious reason this should be the case, but it is true.”