Slide show: Causes of back pain
Illustration of normal and herniated spinal disk
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A tear 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 prevent 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 flexible, and it may develop tears. If it does, the nucleus may bulge out, press on a nerve and cause pain in your back as well as one or both legs.

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