You would be hard-pressed to find a more divisive issue than whether or not it’s cool to crack your knuckles, especially in public.
Some people swear it relieves some pressure or scratches an itch, while the sounds makes other people want to crawl in a silent, black hole.
Whichever side you’re on, you might be curious about what, exactly, is going on in there when they crack – and is it actually good for your body to do it?
For a long time, it was assumed that the cracking noise resulted from a tiny gas bubble collapsing into the synovial fluid surrounding our joints. A 2015 study, which had people crack their knuckles inside an MRI machine, proved differently, however.
They saw the cracking motion actually creating a gas cavity where there was not one previously.
The process is called tribonucleation and has three distinct steps. First, the joint surfaces must be in line before a person applies force. Second, joint surfaces resist the separation. Last, once critical force is reached by pulling the joint surfaces apart, a vacuum-like space appears that’s filled with gas.
Crack!
A follow up study confirmed this conclusion using ultrasound technology, which detects things happening inside the body 100 times faster than MRI.
“What we saw was a bright flash on ultrasound, like a firework exploding in the joint. It was quite an unexpected finding,” said radiology professor and doctor Robert D. Boutin. “That supports the bubble formation theory, not the bubble popping theory.”
In the MRI study, they observed that the cavity remained for a bit before slowly fading away, leaving no visible joint damage in its wake. That said, they only had one participant in their study, so you have to take that particular result with a grain of salt.
That said, previous research into the topic has also found no “detectable immediate adverse effects” from the habit. Despite urban legend, there is also no evidence that cracking your knuckles is linked to arthritis, so people who hate the sound will have to come up with a different excuse.
If you enjoy it, it’s not going to hurt you.
But if you live with someone who hates it, the two of you will have to work that out amongst yourselves.
If you thought that was interesting, you might like to read about why we should be worried about the leak in the bottom of the ocean.