It’s sooo satisfying but is it bad to crack your knuckles? For years we’ve thought that the delightfully disgusting cracking sound was the caused by air bubbles bursting in our joint fluid. Although this was generally considered to be harmless the Is cracking your knuckles bad? debate raged on. Last year researchers at the University of Alberta used MRI video to discover an entirely different reason for the crack. According to study author Gregory Kawchuk, “It’s a little bit like forming a vacuum. As the joint surfaces suddenly separate, there is no more fluid available to fill the increasing joint volume, so a cavity is created and that event is what’s associated with the sound.” In other words, you’re sucking fluid in rather than pushing air out.