Does Cracking Your Knuckles Cause Arthritis? 60 Years of Research Says No
False. No scientific study has found a causal link between knuckle cracking and arthritis. The most famous self-experiment — in which Dr. Donald Unger cracked the knuckles of one hand but not the other for 60 years — found no difference in arthritis development. Population studies confirm this finding.
"Cracking Your Knuckles Causes Arthritis" is a myth. The scientific consensus is clear, the primary sources are documented above, and the exact origin of the false belief can be traced. Read on for the full evidence.
"Cracking Your Knuckles Causes Arthritis"
False.
Few habits generate as much unsolicited parental commentary as knuckle cracking. "Stop that — you'll get arthritis" is a refrain so common it has become a cultural cliché. The claim seems medically plausible: you're stressing your joints, after all. Surely repetitive mechanical stress on cartilage must cause damage over time. But decades of research, including at least one spectacularly committed self-experiment spanning six decades, have failed to find any connection between knuckle cracking and arthritis. The noise is real, the habit is real, but the arthritis claim is not supported by the evidence.
What Is the Cracking Sound?
The popping sound produced by knuckle cracking was the subject of scientific debate for decades. The dominant theory for most of the twentieth century was cavitation: when you stretch a joint, the rapid reduction in pressure causes dissolved gases — primarily carbon dioxide and nitrogen — to form a bubble in the synovial fluid that fills the joint capsule. The sound is the bubble collapsing. This explained why knuckles can't be cracked again immediately after — it takes roughly 20 minutes for the gases to dissolve back into the fluid. A 2015 study from the University of Alberta used MRI to image knuckle cracking in real time for the first time. The researchers found the opposite: the crack corresponds to the formation of the gas bubble, not its collapse. The bubble forms nearly instantaneously and is visible in the MRI images precisely when the sound occurs. A 2018 follow-up study challenged this interpretation, so the exact mechanics remain under debate. But neither study suggested any structural damage to cartilage or bone. The joint produces a sound; it does not sustain measurable harm.
The 60-Year Experiment
In 1998, Dr. Donald Unger received a tongue-in-cheek Ig Nobel Prize for a medical self-experiment that most researchers would never attempt: for 60 years, he cracked the knuckles of his left hand at least twice a day but refrained from cracking the knuckles of his right hand. At the end of the study, he examined both hands for signs of arthritis. He found none in either hand. The experiment was published in Arthritis & Rheumatism and is notable both for its duration and for its use of the contralateral control design — the right hand served as a direct comparison to the left, eliminating most confounding variables. Unger's original motivation was personal: his mother had told him repeatedly that cracking knuckles would cause arthritis, and he wanted to find out. He wrote in his paper: "the conclusion is that there is no apparent relationship between knuckle cracking and the subsequent development of arthritis of the fingers." While a single self-experiment is not definitive proof, it is consistent with every population study that has examined the question.
What Population Studies Have Found
Beyond Unger's self-experiment, several epidemiological studies have examined knuckle cracking and joint health in larger populations. A 1975 study in the Annals of the Rheumatic Diseases by Castellanos and Axelrod examined 74 patients over 45 years old and found no significant difference in arthritis rates between habitual knuckle crackers and non-crackers. A broader study published in the journal Arthritis & Rheumatology in 2011 reviewed the existing literature and found no credible evidence of a causal relationship. What the studies have found, however, is that heavy habitual knuckle crackers — those cracking knuckles many times daily for decades — show slightly increased rates of hand swelling and reduced grip strength compared to non-crackers. The mechanism proposed is ligament stretch, not cartilage damage. These findings don't support an arthritis link, but they do suggest that extremely frequent cracking is not entirely without consequence. Moderate, occasional knuckle cracking appears to be benign by every measure studied.
The Verdict
Cracking your knuckles does not cause arthritis. This has been examined in self-experiments, case-control studies, and epidemiological surveys spanning multiple decades, and no credible evidence of a causal relationship has been found. The crack itself is a gas bubble forming in synovial fluid — not the sound of cartilage grinding. Parents and grandparents may continue to request that you stop, but the arthritis claim is not a valid medical reason.
What Knuckle Cracking Research Has Not Found — and What It Has
The scientific literature on knuckle cracking is somewhat niche, but it is more thorough than might be expected given that the central question — does it cause arthritis? — has a clear and consistent answer. What the research has found is that habitual knuckle cracking is not associated with osteoarthritis of the fingers. This finding has been replicated in case-control studies, prospective cohort studies, and the famous Unger self-experiment. The evidence is not ambiguous. What the research has found, however, is that very heavy habitual cracking — defined in one study as cracking five or more joints multiple times daily for more than 40 years — may be associated with mild, non-arthritic changes: slightly increased hand swelling in some knuckle-cracking joints compared to non-cracked joints in the same hand, and marginally reduced grip strength in some habitual crackers compared to non-crackers. The mechanism proposed is repetitive stretching of the periarticular ligaments — the fibrous capsule surrounding the joint — which over decades may contribute to minor laxity and swelling. These findings are not about arthritis. They do not involve cartilage damage, osteophyte formation, or any of the structural changes characteristic of osteoarthritis. They are also not consistent across all studies. The 2011 Chandran and Bhaskaran literature review found the swelling and grip-strength findings to be limited and methodologically inconsistent. The honest summary of the evidence is: knuckle cracking does not cause arthritis, and moderate habitual cracking appears to be entirely benign. Very heavy, decades-long habitual cracking may have minor effects on joint laxity that do not constitute arthritis. For the vast majority of knuckle crackers — who crack occasionally and casually rather than compulsively and constantly — the evidence provides complete reassurance.
Primary Sources
- [1] Unger, D. L. (1998). Does knuckle cracking lead to arthritis of the fingers?. Arthritis & Rheumatism. ↗ Source
- [2] Chandran, M. & Bhaskaran, S. (2011). Knuckle cracking and hand osteoarthritis. Journal of the American Board of Family Medicine. ↗ Source
- [3] Kawchuk, G. N. et al. (2015). Real-time visualization of joint cavitation. PLOS ONE. ↗ Source
Frequently Asked Questions
Does cracking your knuckles cause arthritis?
No. Multiple studies, including a famous 60-year self-experiment by Dr. Donald Unger and several epidemiological surveys, have found no causal relationship between knuckle cracking and arthritis. The myth likely persists because the habit is socially disliked, making the supposed health consequence feel intuitively plausible.
What causes the popping sound when you crack your knuckles?
The sound is caused by a gas bubble forming in the synovial fluid of the joint when the joint is rapidly stretched. This is called tribonucleation or cavitation. The 2015 MRI study from the University of Alberta visualized this in real time. The joint returns to normal within about 20 minutes as the gas redissolves, which is why you can't crack the same knuckle twice in quick succession.
Is there any harm at all from cracking your knuckles?
Very heavy habitual knuckle cracking (many times daily for decades) has been associated with slightly increased hand swelling and marginally reduced grip strength in some studies. Arthritis is not among the documented effects. Occasional or moderate knuckle cracking appears entirely benign by all available evidence.
Why do some people feel the urge to crack their knuckles?
The urge to crack knuckles is not fully understood but appears to be related to tension relief in the joint capsule. Many habitual crackers describe a sensation of pressure or tightness before cracking that is relieved afterward, similar to how stretching muscles feels relieving. Some research suggests the behavior is partly habitual and partly linked to anxiety relief, but no definitive psychological or physiological mechanism has been established.
What happens inside the joint when you crack your knuckles?
Current evidence points to tribonucleation: the rapid separation of the joint surfaces reduces pressure in the synovial fluid, causing dissolved gases to rapidly form a gas bubble. A 2015 MRI study from the University of Alberta visualized this process in real time, showing the bubble forming at the moment the cracking sound occurs. The bubble dissipates over roughly 20 minutes, which is why you cannot crack the same knuckle immediately again.
Is it possible to crack joints other than knuckles?
Yes. The same gas cavitation mechanism operates in other joints — the spine, knees, toes, and neck are commonly cracked. Chiropractic manipulations produce the same sound through the same mechanism. There is no evidence that moderate cracking of any of these joints causes arthritis, though very forceful manipulation of the neck carries separate risk concerns unrelated to cavitation.
How We Verified This Claim
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For this myth — Cracking Your Knuckles Causes Arthritis — we reviewed the cited primary sources above, cross-referenced against independent scientific literature, and confirmed the verdict with the consensus position of relevant professional bodies (including the sources listed). The claim was then fact-checked against the SmartAss Facts database of over 5,000 verified facts to identify related content.
If you believe our verdict is incorrect or you have a more recent primary source that changes the analysis, the science always wins — we revise pages when the evidence warrants it. Last reviewed: 2026-05.
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