Whether you call it cracking or popping, there is a good chance you were asked to avoid doing it as a child. But does the supposed harm of this habit fall under fact or myth?

We know knuckle cracking is quite common as an estimated 25 to 45 percent of us seem to do it. Before answering the above question, it helps to understand what exactly happens when we "pop" our joints.

For one, that sound of popping does not actually come from your bones. The space in a joint, which is located between two bones, is filled up with synovial fluid. In short, this fluid performs a function similar to that of lubricant, containing the likes of nitrogen and carbon dioxide.

"The noise of cracking or popping in our joints is actually nitrogen bubbles bursting in our synovial fluid," explained Dr. Robert Klapper, an orthopedic surgeon affiliated with Cedars-Sinai Medical Center.

While this was the theory offered by many experts, there does seem to be a bit of debate around it. Some researchers have examined other possible factors contributing to the sound. While one paper examined how bubbles may not completely burst even after the sound, another study suggested that the sound comes from fluid rushing into the cavity

"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," said Greg Kawchuk, a professor at the University of Alberta, Canada who authored the second study.

As for that good feeling you get you crack them just right, it is likely nothing more than "a psychological experience," according to Dr. Klapper — possibly something like the satisfaction you get from popping bubble wrap.  

No matter the mechanism, the question here is whether habitual knuckle poppers are actually at risk of rheumatoid arthritis and related problems. Luckily, there does not seem to be any strong evidence for any such association. At worst, there could be a possible link to lower grip strength, according to past research.

"Finger cracking is so common you would expect to see a lot of causal reports if it was harmful," said Dr. Pedro Beredjiklian, chief of hand and wrist surgery at the Rothman Institute in Philadelphia. "But you don’t. So I think it’s unlikely cracking joints in hands leads to arthritis."

So while the "dangers" you grew up hearing are largely urban myths, experts note that it can worsen a pre-existing injury or problem related to the joint. If you experience any sort of unusual pain or swelling after cracking your knuckles, it may be worth getting them checked by a health professional.