Joint cracking is one of those habits most of us acquire without thinking about it. A knuckle popped mid-sentence. A back twisted as we stand up. A neck gently crunched while the kettle boils. It is common, oddly satisfying and, for anyone sitting nearby, faintly alarming.
It is also surprisingly divisive.
Some people wince at the sound of a knuckle pop or a neck crunch. Others swear by it, twisting, stretching and cracking joints throughout the day in search of relief.
In the third episode of The Conversation’s Strange Health podcast, we turn our attention to one of the body’s most common and least understood noises. Knuckles, backs, knees and necks all feature, along with the enduring warning many of us grew up with: “Stop cracking your joints, you’ll get arthritis.” Is there any truth in it? And why can cracking feel so strangely satisfying?
We turned to this week’s podcast expert guest, Clodagh Toomey, a specialist in musculoskeletal injury and chronic lifestyle-related diseases such as osteoarthritis, to give us the science behind the myths. As she explains in our interview, the familiar popping sound is not bones grinding together. It is caused by a process known as cavitation. Most joints are filled with synovial fluid, which lubricates and cushions movement. When a joint is stretched or twisted, pressure inside it drops suddenly, allowing dissolved gases to form a bubble. The rapid formation or collapse of that bubble creates the cracking noise.
Imaging studies have shown this happening in real time, and decades of research have found no convincing link between habitual knuckle cracking and arthritis. Allergist Donald Unger won the 2009 Ig Nobel Prize in medicine, which recognises quirky research that initially seems trivial or absurd but ends up offering real scientific insight, for his long-running self-experiment. Over decades, he cracked the knuckles on one hand every day and left the other alone, finding no difference between them. Just to prove his mother wrong. You can’t fault his dedication.
So why does it feel good? Part of the answer lies in muscle tension. Stretching a joint stimulates receptors that briefly reduce stiffness and discomfort. Movement also activates sensory nerves that can dampen pain signals, similar to rubbing a sore area after a knock. There may even be a small reward response in the brain, which helps explain why cracking can become habitual.
Neck and back cracking, however, deserves more care. Gentle stretching that produces an occasional crack is usually harmless. Forceful or repeated manipulation, especially by someone untrained, carries more risk. Rare but serious injuries have been linked to damage to blood vessels supplying the brain. These events are uncommon, but they are enough to make aggressive spine cracking a bad idea.
The key message is context. Painless cracking without swelling, locking or loss of movement is usually nothing to worry about. Cracking accompanied by persistent pain, warmth, swelling or a recent injury is a different matter and should be checked out.
Listen to Strange Health to understand why for most people, bone cracking is not a sign of damage or degeneration. It is simply one of the many odd noises the body makes as it moves through the world. Just maybe warn the people sitting next to you first.
Strange Health is hosted by Katie Edwards and Dan Baumgardt. The executive producer is Gemma Ware, with video and sound editing for this episode by Sikander Khan. Artwork by Alice Mason.
In this episode, Dan and Katie talk about a social media clip from loryalien via TikTok.
Listen to Strange Health via any of the apps listed above, download it directly via our RSS feed or find out how else to listen here. A transcript is available via the Apple Podcasts or Spotify apps.
You must be logged in to post a comment Login