Cut your finger accidentally and the area will swell, redden, and heat up. This type of acute inflammatory response is the body's reaction to trauma, and it's an essential part of the healing process. But inflammation can be harmful when it hangs around too long and refuses to leave. When the inflammation switch refuses to turn off, the body operates as if it is always under attack (the older we get, the more likely this is to happen). White blood cells flood the system for weeks, months, and even years.

Researchers are now linking low-grade,...