A person with a herniated disk has weakness in the outer wall of a disk in the spine. This allows the soft tissue that makes up the inside of the disk to push against the weakened wall. As a result, a bulge forms in the side of the disk.

The bulge becomes more prominent when the disk is under stress, during lifting, or twisting of the spine. Sometimes, the bulge can place pressure on the nerves in the spinal canal. About 90 percent of disk herniations occur in the lower back, but they also occur in the neck.