The bones (vertebrae) that form the spine in your back are cushioned by small, spongy discs. When these discs are healthy, they act as shock absorbers for the spine and keep the spine flexible. But when a disc is damaged, it may bulge or break open. This is called a herniated disc. It may also be called a slipped or ruptured disc.

You can have a herniated disc in any part of your spine. But most herniated discs affect the lower back (lumbar spine). Some happen in the neck (cervical spine) and, more rarely, in the upper back (thoracic spine). A herniated disc may be caused by wear and tear of the disc. As you age, your discs dry out and aren't as flexible. Injury to the spine--This may cause tiny tears or cracks in the hard outer layer of the disc. When this happens, the thick gel inside the disc can be forced out through the tears or cracks in the outer layer of the disc. This causes the disc to bulge or break open.

When a herniated disc presses on nerve roots, it can cause pain, numbness, and weakness in the area of the body where the nerve travels. A herniated disc in the lower back can cause pain and numbness in the buttock and down the leg. This is called sciatica. Sciatica is the most common symptom of a herniated disc in the low back.