• So far there have been various theories about the origin of noise.
• Researchers observed the process in the magnetic resonance tomograph.
• There is no indication of whether the cracking is bad or good for the joints.

The cracking noise when pulling apart of fingers formed according to a study by the formation of a cavity in the joint.

Finger in the magnetic resonance tomograph

In the investigation, Greg Kawchuk’s team from the University of Alberta in Edmonton, Canada, took a closer look at a man’s metacarpophalangeal joints in an MRI scanner. The scientists present their results in the journal “PLOS ONE” .

Is there a threat to health?

Some people can crack their joints when they pull their fingers apart. There is currently no evidence as to whether this phenomenon is bad or good for the joints. “So far, no one has ever been able to prove that this  cracking is harmful to health in the long term,” says Professor Jörg van Schoonhoven from the Clinic for Hand Surgery at the Rhön Clinic in Bad Neustadt an der Saale.

Different theories

For a long time there have been various theories about where the popping sound when clicking your fingers comes from. Some scientists suspected that the crackling sound was caused by a bursting bubble in the joint space.

Other researchers hypothesized that the sound is caused by the flapping of ligaments.

Another explanation for the origin of the cracking is what is known as tribonucleation: a mechanism in which the movement of surfaces creates gas bubbles in a liquid.

Study author as guinea pig

To date, there has not been any direct experimental evidence that solidly supports any of the theories. Kawchuk’s researchers wanted to change that. 

For their study, the scientists needed someone who had the ability to crack their metatarsophalangeal joints on request. These joints connect the bones of the metacarpus to the base members of the fingers. The choice fell on Jerome Fryer, one of the study authors.

Pull until it cracks

In the experiment, the researchers examined each finger of the test subject in isolation in a special magnetic resonance tomograph, with which movement sequences can be recorded.

The finger was attached to a kind of tube that was connected to a cable at the other end. Then the cord was pulled until Fryer’s fingers cracked. The entire process in the joint was recorded with an MRI scanner.

Is a cavity the cause?

Shortly before the cracking could be heard, the researchers were able to observe the formation of a cavity in the images.

The scientists therefore assume that tribonucleation has taken place in the joint: “It is a bit as if a vacuum is being formed,” explains Kawchuk in a communication on the study. “If the joint surfaces suddenly separate, there is no longer any liquid left to fill the increasing joint volume. This creates a cavity.” The noise is generated by this event. 

“It is interesting to know what acoustic phenomenon is behind the cracking of the fingers,” said the hand surgeon van Schoonhoven. However, by including only one person in their study, Kawchuk’s researchers would be able to explain the phenomenon only for that person. “The experimental setup does not allow any generalized statements,” said van Schoonhoven.

It can be the cream you put on your face every morning, the beloved hamburger or a habit at the wheel – behind some everyday behavior lurks a danger that hardly anyone knows: you increase the risk of developing cancer. You should therefore leave the following things in the future:

1. Choose your window seat on the plane

Most people enjoy seeing the landscape from above during take-off and landing. Air travelers also like to look at the clouds of cotton wool under the clear blue sky. But if you fly often and sit by the window, you risk skin damage. The window panes keep out most of the UVB rays that cause sunburn. But they let through 47 percent of UVA rays. They are responsible for skin aging and a risk of skin cancer . Because: UV radiation can damage the genetic material. If damaged cells do not die, skin cancer can develop.

2. Insert all receipts

The receipts on thermal paper come from many cash registers and payment devices. And: bisphenol A (BPA). The substance has been classified by the EU as “of very high concern”. It endangers the brain development of the unborn, has been linked to male infertility, and can cause heart disease and cancer. Every time you touch thermal paper, BPA enters the body through the skin and accumulates there. In 2020, an EU-wide ban on thermal paper containing BPA will come into force.

3. Consume very hot drinks

Many people love their soup or tea steaming hot. But whoever swallows liquids above 65 degrees Celsius is putting his esophagus at risk . Because this irritates the tissue and in the long term cell damage occurs, from which cancer can develop.

4. Drive through the rush hour traffic with the window open

As long as there are no clean cars or driving bans in cities, diesel exhaust poses a specific risk for lung and bladder cancer. The WHO investigated this several years ago . Professional drivers or road construction workers are particularly at risk. But you can also get rid of dangerous diesel residues on daily trips through rush hour traffic with stop-and-go movement.

5. Avoid using condoms during sex

Those who live in a monogamous relationship will no longer be infected with the cancer-causing human papilloma virus. Because the greatest risk of HPV infection is unprotected intercourse with changing partners. The most common type of HPV cancer is cervical cancer, which usually develops many years after first exposure to the virus. Infection with certain HPV types can also lead to malignant tumors in the vagina, labia, anus and penis.

6. Use cosmetics with mineral oils

Oils care for the skin, but they shouldn’t be mineral oils. However, these are found in many cosmetic products, from skin cream to lipstick – for example when the ingredients are paraffin, petrolatum or mineral oil. The group of aromatic hydrocarbons (MOAH) poses a health risk. They have the potential to change the genetic makeup and cause cancer. They are filtered out of cosmetics – a decent residue remains, as the testers from the Stiftung Warentester found back in 2015.

7. Drink an after-work beer – or two, three …

Those who drink alcohol not only have an increased risk of liver cancer, but also of mouth and throat cancer and breast cancer. Unsurprisingly, this risk increases with the amount of alcohol. But there is no “safe” lower limit, especially for breast and liver cancer. Various substances that are produced when alcohol is broken down in the body probably play a role here.

8. Staring at your smartphone at night

Studies have shown a link between low levels of melatonin and a higher risk of cancer.The release of the sleep hormone is hindered when light breaks through the nighttime darkness . Smartphones and tablets are a common source of the bright glow in the dark bedroom nowadays. They delay falling asleep or wake the user with incoming messages that are immediately responded to. The sleep cycle is constantly interrupted and chronic sleep disorders develop – a risk factor for cancer.

If you don’t see a doctor, you won’t get cancer because of it. The regular check-ups and preventive appointments with the doctor but can ensure that a tumor early discovered no fatal cancer. The colonoscopy and cervical smear can even prevent abnormal cells from becoming cancer in the first place.