How herniated disks occur:

You may not be able to pinpoint a specific event that caused your disk to rupture. Though it can follow a single, traumatic event, disk herniation is usually the result of a gradual, age-related, degenerative process. Your spine will become stiffer and lose its flexibility as you age. By the time you are 30, your disks begin to show signs of deterioration. They begin to lose their water content, becoming flatter and more brittle as they dry out. Sometimes the disk will swell and bulge out, without actually releasing any of its center fluids. These changes are part of the aging process and account for most episodes of low back pain, though they also can occur without pain.

The tough, fibrous outer covering of the disk is more likely to develop tiny tears as part of this degeneration. Eventually, the jelly-like substance in the center of the disk can come out through the tears, resulting in a herniation or rupture. If the substance pokes out far enough to irritate a nerve, it can cause pain in your back or leg. This typically is called a slipped disk, though the disk is attached firmly between the vertebrae and does not actually move.

Often, before a disk ruptures, you will experience a single occurrence of low back pain or a history of occasional low back pain. But once the disk actually ruptures, the most common complaint is pain that is usually sharp or throbbing and can cause mild to severe discomfort in your back and shooting pain down your leg. If the damaged disk is in the middle or lower part of your back, you also may experience numbness, tingling or weakness in the buttocks, legs or feet. Other symptoms include a shooting pain that occurs if you cough, sneeze or strain, and pain that may become worse after prolonged sitting or standing. Usually only one leg is affected.

Herniated disks occur most frequently in the lumbar spine – between the bottom of your ribs and your hips – and are most common in people in their 30s and 40s.