Sciatica is a type of nerve pain that starts in your lower back or hip and travels down through your buttock, thigh, and sometimes all the way to your calf or foot. It's often described as burning, shooting, or stabbing. For some people, it's just a mild ache. For others, it can be severe and make daily activities hard to manage.

The pain comes from irritation or compression of the sciatic nerve, which is the longest nerve in your body. Figuring out what's triggering your sciatica is key to treating it properly and avoiding long-term problems. Let's go over the six most common causes of sciatica so you can better understand what might be behind your symptoms.

1. Herniated Disc

One of the most frequent causes of sciatica is a herniated disc. Between each bone in your spine, there's a soft disc that works like a cushion. It helps absorb shock and keeps your spine flexible. Sometimes, a disc can bulge or rupture, which is known as a herniated or slipped disc. When this happens in your lower back, the disc can press against the sciatic nerve. This pressure leads to pain that radiates down your leg.

Herniated discs can happen due to injury, aging, or strain from lifting heavy objects. If your sciatica started after a sudden movement or while lifting something, a herniated disc could be the reason.

2. Osteoarthritis

Osteoarthritis is a condition that happens when the cartilage in your joints wears down over time. It's common in older adults and can affect any joint, including the ones in your spine. When this wear and tear occurs in your lower back, it can cause inflammation and stiffness in the small joints between your vertebrae.

This inflammation can irritate the nearby nerves, including the sciatic nerve. In some cases, bone spurs may also form and press directly on the nerve, which makes the pain worse. If you have back stiffness that seems to get worse with age, osteoarthritis might be a factor.

3. Spondylolisthesis

Spondylolisthesis develops when one of your vertebrae slips forward onto a vertebra below it. Dislocated vertebrae in your lower back can protrude into your spinal canal and compress the spinal cord, leading to sciatica. Common causes of spondylolisthesis include degeneration of a vertebra or disc, fracture, injury, or birth defect. If your sciatica pain has occurred after you've suffered an accident or a fall, consult a pain doctor right away to diagnose or exclude the possibility of fracture.

4. Spinal Stenosis

Spinal stenosis is when the spaces inside your spine become too narrow. This narrowing can squeeze the spinal cord or the nerves that branch off from it. When it happens in the lower back, it can compress the sciatic nerve and lead to symptoms of sciatica.

Spinal stenosis usually shows up later in life, often due to degenerative changes. If you notice that standing or walking makes your pain worse but sitting brings some relief, this might be the cause.

5. Muscle Spasms

Muscle spasms in the back or buttocks can also lead to sciatic nerve irritation. When certain muscles become too tight or go into spasm, they can press against the sciatic nerve. This can cause pain that mimics sciatica.

The good news is that muscle-related sciatica often improves with rest, stretching, heat or ice therapy, and anti-inflammatory medications. If your pain seems to come and go or gets worse after a lot of physical activity, muscle spasms could be part of the problem.

6. Piriformis Syndrome

Piriformis syndrome is less common but still worth mentioning. The piriformis is a small muscle deep in your buttocks. The sciatic nerve runs very close to this muscle, or sometimes right through it. If the piriformis becomes tight or inflamed, it can press on the sciatic nerve and cause pain.

Unlike other causes of sciatica, piriformis syndrome isn't usually detected on imaging tests like X-rays or MRIs. Diagnosis is often based on symptoms and physical exams. If your pain seems focused in the buttocks and gets worse when you sit, this could be the cause.