Inflammation is the body’s frontline defense against infection and injury, but when it doesn’t switch off properly, it can drive serious health conditions such as arthritis, heart disease, and diabetes. Until now, scientists didn’t fully understand how the body decides to stop the immune “fight” response and start healing.

Published in Nature Communications, the study reveals that tiny fat-derived molecules called epoxy-oxylipins act as natural brakes on the immune system. These molecules prevent the overgrowth of certain immune cells, known as intermediate monocytes, that can cause chronic inflammation—linked to tissue damage, illness and disease progression.

For the study, healthy human volunteers were given a tiny injection of UV-killed E. coli bacteria into the forearm, which triggered a short-lived inflammatory reaction—pain, redness, heat and swelling—similar to what happens after an infection or injury.