You either do it yourself or know someone who cracks their back, neck, etc. multiple times a day to get some temporary pain relief or just purely out of habit. While the actual cracking and popping most often is not harmful, the repetitive forcing of joints in such a manner may produce chronic, future problems.
The popping sound with joint manipulation is simply a release of gas from the joint. To understand what is going on through the phases of motion, reference the chart below. The physiological zone encompasses both active and passive range of motion until a soft, elastic end feel is felt. The paraphysiological zone is after the physiological zone but just before tissue disruption (i.e. sprains and strains) occurs in the pathological zone. The paraphysiological zone is where manipulation of joints takes place. Just past the limits of passive range of motion, a quick force in the joint into the paraphysiological range usually produces the audible “pop” heard with adjustments (whether it is a self-adjustment or done by someone else). Too forceful of an adjustment or just a traumatic injury puts the joint in the pathological zone causing injury to the surrounding tissues.
That being said, the development of hypermobility is the prime concern with chronic bone crackers. The surrounding ligaments gradually develop laxity allowing joints to move too easily. In response to the hypermobility, the muscles surrounding the joints tighten up to help stabilize the area. When the muscles are tight, the apparent need to crack the joint is there. After the joints are “cracked”, there is temporary relief until the muscles then tighten up again. It is a vicious cycle.
The goal of chiropractic care is to target the hypomobile joints (joints that do not move well) by adjusting these specific areas to get them moving properly again. When there is hypermobility, the goal is to stabilize the area with strengthening exercises. Self-adjusting typically effects the already hypermobile joints, further perpetuating the need to continue to crack the same places over and over again every few minutes.
So in short…is cracking your own spine bad? Yes and no. Occasionally is not bad as long as there is not a lot of force applied. Long term can cause problems created by joints that are too loose and muscles that become chronically tight.