What Is Sciatica and What Causes It?

The sciatic nerve is the longest nerve in the body, running from the lower back through the buttock, down the back of the leg, and into the foot. When it becomes compressed or irritated — at any point along that path — it produces the characteristic symptoms most people recognise as sciatica.

The two most common causes are fundamentally different and require different treatment approaches:

Disc-related sciatica — a disc in the lumbar spine bulges or herniates and presses directly on the nerve root as it exits the spinal canal. This is the most commonly discussed cause and is typically associated with a specific triggering event — a sudden lift, twist, or prolonged sitting — and symptoms that are often worse when sitting or bending forward.

Piriformis syndrome — the sciatic nerve passes through or directly beneath the piriformis muscle in the deep buttock. When this muscle becomes tight or goes into spasm — through overuse, prolonged sitting, or hip mechanics — it compresses the nerve from the outside. Symptoms can closely mimic disc-related sciatica but the treatment is entirely different.

Other contributing causes include facet joint degeneration, spinal stenosis, sacroiliac joint dysfunction, and in some cases referred pain from the hip. Identifying the correct origin is the most important step in getting the right treatment.