I spoke with an orthopedic for this cus my son can crack his knuckles back and also forth for hours at a time, so yes it can damage ur knuckles if u do it enough, n u do it wrong, its like if u take two pointy sticks n run the tips together wat happens? the tips dull. same as cracking. u cause wear n tear on ur joints n den u get arthritis. u wore out ur bone so they start to swell n den they try to fix themselves that's y they may get big n boney , ur body tries to add more bone to the worn out places. then u start to feel sensitivity & or pain then worse case scenario, they end up breaking more easily or often than another normal persons hand.