Childbirth, menstrual cramps, yeast infections.

Women experience pain in ways that no man can. They routinely report more chronic and severe sensory and emotional discomfort in more body parts than men do and experience more pain following injuries.

Even conditions that are not gender specific, such as irritable bowel syndrome, headaches, TMJ (temporomandibular joint) pain, urinary tract infections, arthritis, and fibromyalgia hit women harder, more often, and are less easily relieved than in men, according to Roger Fillingim, a professor of psychology at University of Florida in Gainesville.

Chronic pain, which partially or totally disables 50 million Americans, is a major public health problem in the United States, according to the American Pain Society.

Forty-five percent of all Americans seek care for persistent pain at some point in their lives. While some 36 million Americans missed work in the past year due to pain, women are 50 percent more likely to call in sick than men.

Pain: A Female Complaint?
While pain has long been considered a troublesome female complaint rather than a legitimate symptom that something physically is wrong, experts say the problem is not in a woman's head; it seems to be in her nerves as well.

In studies in which women and men are subjected to the same irritant, women usually give it a higher pain rating. In rat studies, females were more than twice as prone to develop nerve pain than the males.

Why is chronic pain more common in women? At a conference co-sponsored by the Society for Women's Health Research, Georgetown University Medical Center rheumatologist Daniel Claw said women are more sensitive to pain. Claw added that certain autoimmune disorders such as lupus and pain amplification syndromes turn up more frequently in women.

Pain hits women especially hard because of the insomnia, fatigue, loss of appetite, muscle atrophy, and depression that goes along with many such disorders, says James Campbell, a professor of neurosurgery at Johns Hopkins University in Baltimore.

For years scientists have debated the relative importance of brain function, genes, and hormones in causing contrasting pain sensations among men and women. "There is a definite need to better understand all the neurophysiological and psychosocial factors in how we experience pain," says Fillingim. Scientists believe the brain circuitry that regulates pain response and relief differs in women and women.

Women are Wired Differently
Women's hypersensitivity is partly because their brains are wired differently, says Jeffrey Mogil, an assistant professor of psychology at the University of Illinois at Urbana-Champaign.

In research on mice and rats, Mogil and his colleagues implicated a sex-specific gene. The unidentified gene(s) in this region accounts for up to 25% of the trait difference seen in female mice but not males. They also pinpointed a region of a mouse chromosome that contains a gene affecting pain sensitivity only in males.

"More and more it looks like there's actually different systems in men and women...that the physiology must differ by a protein being involved in a neural circuit in one case and not in the other," Mogil says.

Women are more sensitive to the same sensations and less tolerant than males in part because brain chemistry ebbs and flows with the menstrual cycle. New evidence suggests that certain women patients who experience more severe premenstrual pain symptoms may be hypersensitive in other ways.

Fillingim was amazed by how many patients he treated for TMJ had experienced early, painful periods. "They were out of whack from puberty," Fillingim says.

Hormones Linked to Painful Disorders
Hormones have been linked to other painful disorders such as rheumatoid arthritis, irritable bowel syndrome, and fibromyalgia. With such conditions as migraines and TMJ, the prognosis doesn't necessarily improve with age.

A study published in the April 2001 issue of Pain suggests that hormone replacement therapy can actually aggravate TMJ even in healthy menopausal women who are subjected to provocation. "The women on HRT reported being more pain-sensitive than those who were not," says Fillingim, who headed the study.

"If a woman with osteoarthritis starts HRT and notices that her pain is getting worse, she should consider getting off the drug, taking a lower dose, or switching to another alternative to see if (it is) responsible," he says.

From arthritis to migraines, scientists are also finding sex differences in how men and women respond to the pain of common diseases and disorders:

• Arthritis: Daily logs kept by 71 arthritis patients showed that women experienced significantly more severe pain. According to Keefe, who was principal investigator on the project, women are also more likely to relax, air their emotions, seek distractions and emotional support to cope. "Men don't show their feelings and don't seek out assistance as readily as women. That may very well be what's going on in this case," Keefe says.
• Cardiac Disease: Premenopausal women have higher rates of false-positive chest pain syndromes, while postmenopausal women have relatively high rates of asymptomatic or silent heart disease, says Debra Judelson, MD, medical director of the Women's Heart Institute in Beverly Hills, Calif. and former president of the American Women's Medical Association. "Women are more likely to have high blood pressure and diabetes as complicating medical problems which can change the way they experience pain," Judelson says. "They also have more abdominal, shoulder, and neck pain, shortness of breath, back discomfort, vomiting, fatigue and nausea as opposed to chest discomfort seen in men." The bottom line: up to a 40 percent higher mortality rate in younger women under 50 with heart disease than men. "Whatever symptoms they experience are not recognized as a cardio problem in the emergency room, which contributes to delays in seeking help or getting treatment," Judelson adds.
• Migraine Headaches: Boys have more migraines than girls until puberty when hormones begin kicking in. Women are three times more likely to experience migraines than men beginning at puberty when hormone fluctuations kick in. They seem to strike whenever estrogen, the neurotransmitter serotonin, and beta endorphins are low. Several studies concluded that migraine in women of childbearing age dramatically boosts the risk of ischaemic, not haemorrhagic stroke. Women who use oral contraceptives, have high blood pressure, or smoke are at greatest risk of ischaemic stroke associated with migraine.

Opioids More Effective in Women
Scientists believe that learning about sex differences in pain may require rethinking how much medication to give people based on their sex. A 2001 study found that women patients with myocardial infarction (heart attack) were less likely than men to receive aspirin in the first hour of care than men.

Evidence suggests men and women respond differently to certain drugs, including analgesics used to treat pain. Campbell indicated that one study found that for back pain, male physicians prescribed higher doses of pain medication while female physicians upped pain medication for women. As the founder of the American Pain Society, Campbell urges more, not less, prescribing of painkillers to those in need.

Despite the fact that painful problems disproportionately strike women, the bright side is that a class of pain relievers called opioids are more effective in women although Campbell insists that their effects vary with the menstrual cycle.

To get pain relief, he insists, often calls for a variety of treatments, not a single solution. "The bottom line is helping that person relieve the level of pain and suffering, sleep, and function for daily living." Claw agrees. He prescribes medications that act on neurotransmitters, exercise, and cognitive therapy.