Slide show: Causes of back pain
Illustration of normal and herniated spinal disk
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A crack in one of the spinal disks — rubbery cushions between the vertebrae — may cause back pain or play a role in the development of back pain. Spinal disks protect the stacked vertebrae from rubbing against each other. The outer layer (annulus) of each disk is normally tough and pliable. The inner layer (nucleus) is soft.

A spinal disk can gradually develop aging-related changes that cause or contribute to back pain. There's less water within the annulus, so it's not as stretchy, and it may crack (herniate). If it does, the nucleus may bulge out, press on nerves and cause back pain.

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