Chronic pain lasts longer for women than men, and new research suggests differences in hormone-regulated immune cells, called monocytes, may help explain why.

In a new paper in Science Immunology, researchers at Michigan State University found a subset of monocytes release a molecule to switch off pain. These cells are more active in males due to higher levels of sex hormones such as testosterone, the team found.

Females, however, experienced longer-lasting pain and delayed recovery, because their monocytes were less active. Geoffroy Laumet, MSU associate professor of physiology, and Jaewon Sim, a former graduate student in his lab, discovered the same pattern in both mouse models and human patients.