Why Are Women More Sensitive to Pain Than Men?
To answer that question and others, we interviewed Roger B. Fillingim, PhD, a Distinguished Professor at the University of Florida, College of Dentistry, and the Director of the University of Florida Pain Research and Intervention Center of Excellence (PRICE) in Gainesville, Florida. Dr. Fillingim also is Immediate Past President of the American Pain Society.
Q: Why do men and women experience pain so differently?
Dr. Fillingim: Pain is a complicated experience that is influenced by many variables in the body—from how your nerves send and receive information, to how your brain handles information about pain coming from the nerves, to how much inflammation is in your body.
In general, women experience higher levels of pain and are more likely to have certain pain disorders than men. While we don’t know all of the factors that affect the pain experience, we do know that men and women’s brains and bodies respond differently to pain.
Hormones may play a role in women having more pain sensitivity. In addition, women have greater nerve density (more nerves in a given area of the body)—which may cause women to feel pain more severely than men.
In addition, women’s psychological experience of pain differs from men’s in certain ways. For example, women are more likely to worry about pain and feel more helpless about it, and are more likely than men to have depression and anxiety, all of which can lead to higher pain levels. On the other hand, women have a broader range of pain coping skills than men, which may be helpful in some cases.
Q: Women are more likely to have depression and anxiety than men. Does this affect how they feel pain?
Dr. Fillingim: Higher levels of anxiety and depression can increase your risk of developing a new chronic (long-term) pain condition in the future. Likewise, people with chronic pain are at risk for developing anxiety and depression in the future.
We don’t know why that is, and studies have not shown that depression or anxiety actually causes pain, or vice versa. We do know that some of the parts of the brain responsible for mood overlap with the parts of the brain responsible for feeling pain. Also, some neurotransmitters (messengers in the brain) that are involved in mood symptoms are involved in pain, including serotonin and norepinephrine. In addition, people who experience high levels of stress or traumatic events are at greater risk for depression/anxiety as well as for pain disorders, so there may be some overlapping effect there as well.
People who have mood issues and pain need to be treated for all of these conditions in order to have a good outcome. Some medications help all of the issues at the same time. In addition, exercise is known to improve both pain and mood.
Q: Does sex (physical differences) or gender (male versus female experience) influence pain more?
Dr. Fillingim: We tend to view sex and gender as separate things: one is physical and one is more social and psychological. In truth, sex and gender are highly interactive and both contribute to differences in pain among women and men.
For example, people often assume that gender roles are what we learned when our parents doted on the little girl when she got hurt and ignored the little boy when he got hurt. However, gender role behavior is detected very early in life and is related to hormone level exposure before birth. There is a biology to gender roles above and beyond any social learning that occurs.
Q: Why are premenopausal women at greater risk for pain conditions than postmenopause women?
Dr. Fillingim: Women are at greater risk for several chronic pain conditions—including migraine headache, temporomandibular disorder (TMD), and stomach pain from irritable bowel syndrome. The sex differences in the risk for these disorders is the largest during the reproductive years (around ages 20 to 40 years) and then tends to decrease later in life because postmenopausal women (who no longer menstruate) are less likely to have these conditions than premenopausal women (who still menstruate). Some research suggests that female hormones—namely estrogen—are related to the greater risk for these pain conditions in premenopausal women versus postmenopausal women and men.
However, other pain conditions like arthritis and neuralgia (nerve pain) are more common in older people in general and, thus, are more common in postmenopausal women than younger women.
Q: Do women respond differently to pain medications than men?
Dr. Fillingim: For pain medications known as opioids (eg, morphine, hydromorphone, codeine, oxycodone), women tend to get more pain relief, but they also have more side effects. Thus, women may be able to take lower doses of opioids than men, lowering the risk for the side effects, while still getting the same amount of pain relief as men. It is unclear if this is true for pain medications other than opioids.
Regardless of whether you are a woman or man, there are tremendous differences in how people in general respond to different treatments. Some treatments are only helpful for a minority of patients. Thus, it often takes some trial and error in order to find the best treatment. If the first treatment doesn’t work, it is worth pursuing other treatments before giving up.
Q: Many studies of sex differences in pain involve animals instead of humans. Do results from animal studies always apply to humans?
Dr. Fillingim: Findings from animal studies sometimes translate to humans and sometimes do not. For example, female mice are slightly more pain sensitive than male mice, which is also the case in humans. On the other hand, male mice consistently receive better pain relief from opioid medications than female mice, which is the opposite of what we see in humans.
One problem with using mice to study pain is that women and female mice have different reproductive cycles. [Mice go into heat every 4 to 5 days all year round]. Thus, the influence of hormones on pain in female mice might be different from that in women. Mice also have less developed brains than humans, especially in an area known as the cortex, which is used to process pain.
While there are limitations to using animals to study pain, a lot of what we have learned about pain in humans has been gained through studies in non-human animals.
Q: Shouldn’t enduring childbirth make women more tolerant of pain than men?
Dr. Fillingim: While most people think that women are more pain tolerant than men because of childbirth, the opposite is actually the case. However, during pregnancy, hormones are released that are believed to make women less pain sensitive. This “pregnancy-induced analgesia” has been shown in some studies involving women, but is consistently found in animal studies. Pregnancy-induced analgesia has even been found in male rats that are injected with pregnancy hormones.
The pain experienced by women in labor appears to depend a lot more on factors such as how anxious or fearful the mother is about childbirth, lack of labor support during childbirth, and how excited the woman is about the pregnancy