Why Does Your Back Hurt?
Back Pain Has Many Suspects — Not Just One
The lower back contains several structures that can each generate pain. In most cases, more than one is involved at the same time.
1. Discs — The Spine's Shock Absorbers
Involved in an estimated 26–42% of chronic low back pain cases
Spinal discs sit between each pair of vertebrae and absorb impact. Over time, the outer wall of the disc (the annulus) can develop small tears. When nerves and blood vessels grow into these tears, the disc itself becomes a source of pain.
Typical pain: A deep, dull ache in the center of the lower back. Tends to worsen with prolonged sitting and improve when you stand up.
Key fact: Disc degeneration appears on MRI in 37% of 20-year-olds and 96% of 80-year-olds — even when they have no pain at all (Brinjikji 2015).
2. Facet Joints — The Spine's Small Hinges
Involved in an estimated 15–45% of chronic low back pain cases
Facet joints are pairs of small joints at the back of the spine that guide and limit movement. Like any joint, their cartilage can wear down over time, leading to arthritis.
Typical pain: Pain on one or both sides of the lower back. May spread to the buttocks or upper thighs. Tends to worsen with bending backward or twisting.
Important: Even when imaging shows facet joint changes, those changes may not be causing the pain. About 10% of people in their 30s already show facet changes on imaging, and the frequency of these changes is similar in people with and without pain (Borenstein 2004).
3. Sacroiliac (SI) Joint — Where the Spine Meets the Pelvis
Involved in an estimated 10–30% of chronic low back pain cases
The SI joints connect the base of the spine (sacrum) to the pelvis (ilium) on each side. They transfer the weight of the upper body to the legs. Childbirth, leg length differences, prior spinal surgery, and inflammatory conditions can all contribute to SI joint pain.
Typical pain: Pain in one buttock that you can point to with a finger. May spread to the groin area.
4. Muscles and Fascia — The Back's Support System
Involved in an estimated 30–85% of pain clinic patients
Muscle injuries, overuse, and prolonged poor posture can produce "trigger points" — tight, tender knots within muscles. These can cause local pain and also refer pain to other areas of the body.
Typical pain: Sore, tight spots that hurt when pressed, with pain that seems to spread or radiate. Tends to worsen with stress and fatigue.
5. Central Sensitization — When the Volume Gets Turned Up
Central sensitization is a relatively recent concept in pain science.
When pain persists for weeks or months, the nervous system — the spinal cord and brain — can shift into a heightened state. It's like someone has turned up the volume dial on your pain processing, without you realizing it.
When this happens:
- Stimuli that shouldn't hurt (light touch, gentle pressure) start to cause pain
- Mild pain signals get amplified into severe pain
- Pain persists even after the original tissue has healed
This is not "all in your head." It is a real, measurable change in how the nervous system functions. The International Association for the Study of Pain (IASP) has given this type of pain its own name: nociplastic pain — meaning pain that arises from altered processing in the nervous system itself.
Research has shown that poor sleep, chronic stress, anxiety, and depression can all worsen central sensitization (Nijs 2018).
6. Spinal Stenosis — A Narrowing That Can Also Cause Back Pain
Spinal stenosis (another topic covered in detail on this site) is typically known for leg symptoms — numbness, tingling, and difficulty walking. However, the same changes that cause stenosis — enlarged facet joints, thickened ligaments, degenerating discs — can also generate lower back pain itself.
For more on spinal stenosis → What Is Spinal Stenosis?