12 Health Mysteries Explained

Why Do Joints Crack?

When you stretch a joint by, say, pressing down on your knuckles or twisting your spine, you cause small air bubbles that form between the sacs in the joints to pop. These sacs, called bursas, help cushion the spaces between the bones and keep them lubricated. As creepy as the sound can be, cracking is usually harmless and has no effect on the bursas. “Despite what your mom may have told you, cracking your knuckles or ankles or knees or any other joint doesn’t cause arthritis,” Applegate says. But it doesn’t do your joints any good, either. “Any feel-good benefit people claim from joint cracking,” he says, “is psychological.”