A researcher at the University of California did a study to find out what causes the noise when you crack your joints.
He asked participants to crack their joints while he performed an ultrasound.
When the joint was cracked the researcher saw a bright flash of light on the ultrasound, “like a firework exploding in the joint”.
The flash of light is thought to be from sudden change in the pressure of the fluid in the joint, called the synovial fluid.
The researchers found no damage to the joints of people who habitually crack their joints. The images showed no difference in the joints of habitual knuckle crackers compared to those who never crack their joints.