When a disc is compressed from normal wear and tear over time, the soft jelly-like center squeezes into cracks in the outer layer. This makes the disc bulge out from between two bones in the spine (vertebrae).
Discs are rubbery cushions between the bones in the spine that absorb shock when you walk or run. They’re made of soft cartilage in the center surrounded by a layer of tough cartilage. Cartilage cushions and protects joints and prevents them from rubbing against each other.
A bulging disc isn’t usually painful unless the disc presses against a nearby nerve. It’s usually caused by normal wear and tear on the spine.