Women’s pain last longer than men’s. A study offers an explanation.

Scientists who study chronic pain have long wondered about a particular type of scenario: A man and a woman are involved in a car accident and suffer the same injuries. But the woman feels lasting pain, while the man recovers more quickly.

Historically, some doctors have dismissed these differences, saying women exaggerate their pain or are unable to tolerate the same discomfort as men. But studies have repeatedly shown that women are more likely to suffer from chronic pain in general and that their pain lasts longer on average.

A study published Friday in the journal Science Immunology provides some insight into why: Men’s immune systems may have a better mechanism for stopping pain, likely because of their higher testosterone levels.

“What we show is that this is a real biological mechanism coming from immune cells. It’s not in the mind,” said Geoffroy Laumet, one of the study’s authors and an associate professor of physiology at Michigan State University.

Ann Gregus, an assistant professor at Virginia Tech who studies ways to treat chronic pain, said the findings underscore the need to take women’s pain seriously.

“A lot of women learn to hide their pain, because if they don’t, people will feel like they can’t do their job, that they can’t take care of their family,” said Gregus, who was not involved in the new study.

The results apply to persistent pain after surgery or physical trauma. However, other chronic pain conditions, such as fibromyalgia, do not follow a traumatic event.

“Does this explain everything? I don’t think so. We don’t have a single magic pathway,” said Dr. Michele Curatolo, a professor of anesthesiology and pain medicine at the University of Washington, who was not involved in the new research. Curatolo is the chief medical officer of 4E Therapeutics, a neuroscience company developing treatments for pain.

For the new study, researchers asked 245 people who had suffered traumatic injuries – mostly car accidents – to rate their pain levels. Although men and women experienced approximately the same intensity of pain on the day of injury, men saw their pain disappear more quickly over a period of nearly three months.

Blood tests showed that men had higher levels of a molecule called interleukin-10, which cuts off pain signals sent to the brain. Laumet said testosterone increases the production of interleukin-10 from white blood cells.

The same was true in laboratory experiments involving mice.

The team of scientists gave injections to mice to stimulate an inflammatory response, and afterward, male mice showed signs of resolution of their pain, while female mice did not. Male mice also recovered more quickly from a small surgical incision and restraint in a tube for two hours – a scenario designed to mimic the physical and emotional stress of a car accident.

In experiments with mice, the white blood cells that produce interleukin-10 were much more active in males.

Gregus said the new research likely reflects evolutionary differences between men and women.

“This builds on a series of studies that have been done to show that men tend to use their innate immune systems more effectively than women,” she said. (The innate immune system is the body’s first line of defense against foreign invaders.)

But Curatolo added that gender differences aren’t black and white — and men often have long-term pain, too.

In the long term, Laumet said, the findings could be used to develop new treatments for chronic pain in women, such as testosterone patches. Topical treatments like this tend to have fewer side effects than systemic medications, he said.

As it stands, many of the current options for chronic pain relief have concerning side effects and do not completely relieve symptoms. Long-term use of over-the-counter pain relievers can lead to kidney damage or stomach ulcers. Opioids, often prescribed as a last resort, can be addictive. Doctors sometimes even prescribe off-label antidepressants or antiepileptic medications for pain relief, but many patients with chronic pain do not respond to them. And physical therapy or acupuncture may work for some patients but not others.

“We clearly need alternative options,” Gregus said.