Watch: This Is What Really Happens When You Crack Your Knuckles

Update: A new paper, published this week in PLOS, includes this fascinating video of a knuckle cracking in an MRI machine. Continue to our original story below to learn more about what's happening here.  This story was originally published on March 9, 2015. Cracking your knuckles can be as satisfying as popping bubble wrap, but is it actually harmful to your joints? And, what is that noise? This new video from Vox has all the answers. The video explains that synovial fluid, a "lubricant-like substance" found in between your joints, releases a gas when you stretch out your knuckles, for example. This gas forms bubbles which pop, resulting in the cracking sound that so many people despise. As for the age-old debate regarding the dangers of knuckle-cracking, Vox cites two studies. The first won researcher Donald Unger the Ig Nobel Award in Medicine in 2009. After cracking the joints in his left hand, but not his right hand, for 60 years, he concluded (as conclusively as one can when they are the lone subject of their own study) that cracking joints would not cause arthritis. On the other hand, Vox brings up a 1990 study that found that snapping, cracking, and popping can lead to a decrease in grip strength and an increase in hand swelling. Knuckle-crackers of the world, you may take this all to mean your habit isn't that dangerous after all. But, we're with Vox on one conclusion: It's still as annoying as ever. 

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