Anyone who has ever had a pimple is familiar with the tissue redness, swelling, warmth and pain that mark an infection. This response, known as inflammation, has been recognized since ancient times. But the process, which is often set in motion by cells of the immune system, can also occur whenever tissue is damaged—even in the absence of a pathogenic organism—as, for example, when you stub your toe or, more seriously, suffer a heart attack. This second condition is called sterile inflammation, and when it goes awry, it contributes to a wide range of seemingly unrelated medical conditions, from Alzheimer's disease to diabetes to various liver conditions.