Why Do Women Experience Prolonged Pain? Immune Cells Could Hold the Answer

Pain is a common aftermath of injuries such as a sprained ankle, surgery, or car accidents. Typically, this discomfort subsides as the body recovers. However, studies indicate that women often experience prolonged pain, which increases their risk of developing chronic pain conditions more so than men.

For many years, the disparity in pain experiences between men and women has been largely attributed to psychological, emotional, or social factors. This perspective has frequently led to the oversight of persistent pain in women within healthcare settings.

Recent findings from my research team, however, point to the immune system as a potential factor in the differing pain recovery rates between the genders. Traditionally, doctors have believed that the immune system exacerbates pain by triggering inflammation, recognizable by redness and swelling.

Nonetheless, our latest research, along with similar studies, suggests that immune cells might also play a crucial role in pain resolution. Variations in the functioning of these cells between men and women could explain why women often experience prolonged pain.

Hormones and immune cells

As a neuroimmunologist focused on the interaction between the nervous and immune systems, my research team is dedicated to uncovering the reasons behind pain that lingers long after an injury has healed, eventually becoming chronic.

To study this process, we combined experiments in mice with data from people who had been involved in motor vehicle collisions. This type of injury is a common trigger for long-term musculoskeletal pain, making it an ideal situation to study how acute pain becomes chronic.

We focused on a specific molecule called interleukin-10 that helps reduce inflammation, measuring its levels in both mice after skin injury and in people in the emergency room after a motor vehicle accident. Surprisingly, we found that IL-10 doesn’t just calm inflammation. It also communicates directly to pain-sensing nerve cells to switch them off. In other words, IL-10 helps pain to go away.

We identified that IL-10 was mostly produced by a type of immune cell called monocytes that circulate in the blood and travel to injured tissues.

Across both mice and humans, we found that males tended to recover from pain more quickly than females. The reason appears to lie in how monocytes behave after injury. In males, these immune cells were more likely to produce IL-10, the molecule that helps resolve pain. In females, this response was less pronounced.

Importantly, we also found that testosterone influences how much IL-10 these immune cells produce. Higher levels of testosterone in males promoted higher production of IL-10 by monocytes.

This finding suggests that hormonal signals may shape the body’s ability to naturally turn off pain after injury.

Avenues for treatment

Our results point to a shift in how scientists think about pain: Rather than viewing the immune system only as a driver of pain, it may also be a key player in resolving it. Differences in immune cell function could explain why some people recover quicker from injury while others go on to develop chronic pain.

Understanding these biological pathways could eventually lead to new treatments. Instead of simply blocking pain signals, future therapies might aim to boost the body’s own pain resolution system. Helping immune cells calm down pain-sensing neurons more effectively could more quickly restore comfort after injury.

While more research is needed, these results highlight a promising new direction in the effort to prevent and treat chronic pain and better understand sex differences in pain.