Things we learned as a kid: If you make a weird face, it
could freeze like that; if you step on a crack, you will break your mamma's
back; if you crack your knuckles, it’s going to give you arthritis later in
life.
Fortunately, kids are dumb and don’t know anything. Cracking
your knuckles does not cause arthritis. But that's not the whole story...
Science is still not entirely sure what the noise is when
you crack a knuckle. It could be air bubbles moving around your joint, but
there is more evidence to support that your joints have small caves of air that collapse and fill with fluid when you squeeze, making that popping sound.
In fact, after a joint has been “cracked,” there is a window
of time known as a refractory period (around 20 minutes) where the joint can’t
be cracked again, as the gases are getting reabsorbed into the joint fluid,
known as synovial fluid.
It’s crazy how, as much as we know about the human body,
scientists aren’t totally sure if the sound is from the bubble of air forming
or collapsing. A team of scientists even tried to prove the sound was from the air bubble formation in 2015,
but it’s still a controversial opinion due to lack of physical evidence.
Scientists have studied knuckle-crackers long term, though, and found no greater increase for arthritis later in life. Some people with arthritis have more crackable knuckles and people with
arthritis can hear a crack due to swollen tissue, but that’s a reversal of
cause and effect.
Snapping tendons can also crack like rubber bands every now
and then, but that’s not likely the same as knuckle-cracking.
However, there is a risk of chronic knuckle-crackers having more swelling in their hands and lower grip strength. This is definitely not arthritis, but not great news for crackers. There's also the chance that all that squeezing of your hand could lead to
knocking something out of place and injuring yourself.
Some people crack their knuckles because they say it feels
good. While all these fluids and gasses move around, joints may feel looser.
Some do it because they’re addicted to sound, like snapping gum. Most likely though,
those around you may not enjoy the habit as much, and at the end of the day, it's more annoying than unsafe.
TL;DR: As far as developing arthritis is concerned, that is not a problem for knuckle-crackers. But there is a small risk of weakening your hands or causing an injury, as well as annoying those around you and possibly getting punched in the face.