Does knuckle cracking lead to arthritis of the fingers Donald L. Unger?

September 22, 2025 •

4 min read

According to the satirical Ig Nobel Prize awarded in 2009, an American physician conducted a single-subject experiment lasting 50 years to investigate a popular health myth. This groundbreaking (and slightly humorous) study led by Dr. Donald L. Unger aimed to answer the age-old question: Does knuckle cracking lead to arthritis of the fingers Donald L. Unger?

Quick Summary

Dr. Donald L. Unger's decades-long self-experiment, backed by broader scientific studies, suggests that habitual knuckle cracking does not cause arthritis of the fingers. The common belief linking the two is a persistent myth, and the popping sound is simply the release of gas bubbles within the joint fluid. Unger found no difference in arthritis prevalence between his cracked and uncracked hands, a finding that has since been supported by larger clinical research.

Key Points

The Arthritis Myth: Contrary to popular belief, habitual knuckle cracking does not cause arthritis, a finding supported by multiple scientific studies and a famous 50-year self-experiment by Dr. Donald L. Unger.
Gas Bubble Collapse: The popping sound comes from the rapid formation or collapse of gas bubbles (cavitation) in the synovial fluid that lubricates your joints, not from bones rubbing together.
Unger's Famous Experiment: Dr. Unger cracked only the knuckles on one hand for five decades and found no difference in arthritis development between his hands, earning him a satirical Ig Nobel Prize.
Minor Side Effects: While not a cause of arthritis, chronic knuckle cracking may be associated with minor issues like temporary hand swelling or reduced grip strength, though evidence is inconsistent.
Underlying Causes: The true causes of arthritis are typically age, genetics, and joint injuries, not the habit of knuckle cracking.
When to See a Doctor: If knuckle cracking is accompanied by pain, persistent swelling, or limited motion, it could indicate an underlying joint issue that should be evaluated by a healthcare professional.

Dr. Unger's Decades-Long Experiment

For over 50 years, Dr. Donald L. Unger, a physician from California, conducted a remarkable and somewhat unusual scientific study on himself. Driven by his mother's repeated warnings that cracking his knuckles would give him arthritis, he decided to test the theory rigorously. His method was simple but effective: he cracked the knuckles on his left hand at least twice a day, every day, while leaving the knuckles on his right hand untouched. Over the course of five decades, he estimated cracking the joints on his left hand more than 36,500 times.

The Ig Nobel Prize and Unger's Conclusion

When Unger finally examined the results of his lifelong experiment, he found no difference in the prevalence of arthritis between his two hands. He published his findings in a 1998 letter to the journal Arthritis & Rheumatism, a publication not typically known for such anecdotal reports, and later received the satirical Ig Nobel Prize in Medicine in 2009 for his dedication to challenging a widespread health myth. His simple conclusion? There is no apparent relationship between knuckle cracking and the development of finger arthritis.

The Science Behind the 'Pop' and the Myth's Persistence

So, if it’s not bones grinding together, what causes the cracking sound? The prevailing scientific theory involves a process called cavitation. Your finger joints are encapsulated in a membrane containing synovial fluid, a natural lubricant that allows your bones to glide smoothly against one another. This fluid contains dissolved gases, such as carbon dioxide and nitrogen. When you stretch or bend your finger, you increase the space between the bones, causing a sudden drop in pressure within the joint capsule. This pressure change causes the dissolved gases to rapidly form a bubble, and the audible 'pop' is the sound of that bubble either collapsing or forming. It takes about 20-30 minutes for these gases to re-dissolve into the synovial fluid, which is why you can't crack the same knuckle twice in a row.

Why the Myth Persists

The long-standing myth linking knuckle cracking to arthritis likely stems from a common-sense but incorrect assumption. The idea that a loud, repetitive motion must be causing damage to delicate joints is a logical, but unfounded, fear. Additionally, some people who already have joint pain or stiffness, which could be an early sign of arthritis, may also have a habit of cracking their knuckles, leading them to mistakenly believe the cracking is the cause of their pain.

Further Research Supporting Unger's Findings

Dr. Unger's anecdotal experiment, while compelling and memorable, was just one piece of a larger scientific consensus. Other, more rigorous studies have also looked into this topic and confirmed his results.

Study Comparisons


Study	Participants	Age Range	Conclusion	Supporting Reference
Swezey and Swezey (1975)	28 nursing home residents	Not specified	No correlation between knuckle cracking and arthritis.
Castellanos and Axelrod (1990)	300 individuals	Over 45	Found no increased prevalence of hand arthritis among habitual knuckle crackers.
Deweber, et al. (2011)	215 individuals	50 to 89	Found no significant correlation between knuckle cracking and hand osteoarthritis.
Unger (1998)	1 (self-experiment)	50 years	Found no difference in arthritis between cracked and uncracked hands.

Are There Any Risks?

While the arthritis myth is debunked, some studies have noted minor potential downsides associated with habitual knuckle cracking. Some research has suggested chronic knuckle cracking might lead to temporary hand swelling or a reduction in grip strength, though results are inconsistent. Most experts agree these effects are minor and reversible. More serious risks, such as ligament damage or dislocation, are extremely rare and typically only occur with excessive, forceful, or non-habitual attempts to crack a joint.

Final Verdict and Health Recommendations

For the vast majority of people, knuckle cracking is a harmless habit that does not cause arthritis. The science is clear on this point, thanks in part to Dr. Donald L. Unger's dedicated, if quirky, experiment. The real culprits behind conditions like osteoarthritis are typically age, genetics, previous joint injuries, and general wear and tear, not the satisfaction of a good joint pop.

To ensure your joint health remains in top condition, focus on proven strategies:

Maintain a balanced and healthy diet.
Engage in regular exercise to keep joints mobile.
Be mindful of repetitive strain and use proper ergonomics, especially if you have a desk job.
If you experience pain, swelling, or persistent discomfort when your joints crack, consult a healthcare professional. Pain is a signal that should not be ignored.

So, you can finally put your mother's fears to rest. Knuckle cracking might be an annoying habit to those around you, but it won't ruin your joints. The most authoritative research consistently points to the fact that there is no link between the two. For further information on joint health, you can visit the Arthritis Foundation's website.

Frequently Asked Questions

Yes, Dr. Donald L. Unger performed a 50-year-long self-experiment to prove his mother wrong. By cracking the knuckles on one hand every day and leaving the other alone, he demonstrated that there was no difference in arthritis between his two hands, a conclusion that has been supported by larger, more formal scientific studies.

The popping sound is caused by a process called cavitation. When you stretch your joint, you create a low-pressure space within the synovial fluid, causing dissolved gases to rapidly form or collapse, which produces the audible 'pop'.

Yes. Osteoarthritis, the most common form of arthritis, is typically caused by factors like age, genetics, obesity, and joint injuries from repetitive strain or trauma. Knuckle cracking is not a contributing factor.

For most people, the habit is harmless. However, some studies have noted potential minor side effects, such as temporary swelling or, in rare cases, a decrease in grip strength. Serious injuries like ligament damage are extremely uncommon and usually only result from aggressive or forceful joint manipulation.

The feeling of relief often comes from the act of stretching your fingers and the release of gas bubbles, which can provide a sense of increased joint mobility or release nervous energy. This can also be a psychological effect for some people.

While it won't lead to arthritis, excessive or forceful cracking could potentially irritate the joints and surrounding tissues over time. If you experience pain or discomfort, it's a good idea to stop.

Based on current evidence, you can assure your children that they won't get arthritis from the habit. While it's largely harmless, it's a personal preference whether to encourage or discourage the behavior due to the sound and social implications.