Cracking your knuckles may aggravate the people around you, but it probably won't raise your risk for arthritis. That's the conclusion of several studies that compared rates of hand arthritis among habitual knuckle-crackers and people who didn't crack their knuckles.
The "pop" of a cracked knuckle is caused by bubbles bursting in the synovial fluid — the fluid that helps lubricate joints. The bubbles pop when you pull the bones apart, either by stretching the fingers or bending them backward, creating negative pressure. One study's authors compared the sudden, vibratory energy produced during knuckle cracking to "the forces responsible for the destruction of hydraulic blades and ship propellers."
Even if knuckle cracking doesn't cause arthritis, there's still good reason to let go of the habit. Chronic knuckle-crackers were more likely to have swollen hands and reduced grip strength. And there are at least two published reports of injuries suffered while people were trying to crack their knuckles.
For more information on keeping your hand healthy, nimble, and strong, buy Hands: Strategies for Strong, Pain-Free Hands, a Special Health Report from Harvard Medical School.