Fibromyalgia doesn’t have a single cause. It develops when a combination of genetic vulnerability, nervous system changes, and environmental triggers converge to rewire how the brain processes pain. Women are twice as likely to develop it as men, and most people are diagnosed during middle age, though it can start at any point in life.
What Happens Inside the Nervous System
The core problem in fibromyalgia is something called central sensitization: the brain and spinal cord become overly responsive to pain signals. Normally, your nervous system has a built-in volume control. Signals traveling up from the body (“this hurts”) are balanced by signals traveling down from the brain (“not that much, calm down”). In fibromyalgia, both sides of this system malfunction. The ascending pain signals get amplified while the brain’s ability to dial them back weakens.
This isn’t a metaphor. Structural, functional, and chemical changes in the central nervous system drive this shift. People with fibromyalgia have elevated levels of excitatory brain chemicals like glutamate and substance P, which make nerve cells fire more easily. At the same time, they have lower levels of serotonin and norepinephrine in the spinal pathways responsible for suppressing pain. The result is a nervous system stuck in a state of high alert, where ordinary sensations like pressure, temperature changes, or even normal muscle fatigue register as painful.
Over time, neuroplasticity (the brain’s ability to reorganize itself) works against the person. A progressively larger area of the brain becomes dedicated to processing pain signals, while the regions responsible for dampening those signals shrink in capacity. This is why fibromyalgia tends to worsen or spread rather than stay confined to one area.
The Role of Genetics
Fibromyalgia runs in families, and large-scale genetic studies are beginning to explain why. A study analyzing data from 2.5 million individuals found that fibromyalgia’s genetic signature is concentrated almost exclusively in brain tissues and neural cell types, reinforcing the idea that this is fundamentally a nervous system condition. Several genes involved in how nerve cells communicate and connect were implicated, including genes tied to dopamine signaling and neural development.
Having a close relative with fibromyalgia raises your risk, but genetics alone don’t determine whether you’ll develop it. Think of the genetic component as a loaded gun: it creates vulnerability, but something else usually pulls the trigger.
Common Triggers That Start the Process
Many people can trace the onset of their fibromyalgia to a specific event. Physical trauma is one of the most recognized triggers, particularly injuries that flood the nervous system with prolonged pain signals. Car accidents are a classic example. Major surgeries can have a similar effect, especially when recovery involves weeks or months of pain that keeps the nervous system in overdrive.
Infections are another well-documented trigger. Epstein-Barr virus (the virus behind mono) and Lyme disease both appear capable of setting off the cascade of nervous system changes that lead to fibromyalgia. The mechanism likely involves immune activation following the infection, which alters how the brain and spinal cord handle incoming signals even after the infection itself has cleared.
Severe emotional stress or psychological trauma can also be a starting point. Military combat, abuse, the death of a loved one, or other profoundly stressful experiences activate the sympathetic nervous system (your fight-or-flight response) for extended periods. This sustained state of physiological stress appears to push a vulnerable nervous system toward central sensitization.
Sometimes, though, fibromyalgia develops without any obvious trigger at all. The process may be gradual enough that no single event stands out.
Sleep Disruption Feeds the Cycle
Poor sleep isn’t just a symptom of fibromyalgia. It actively contributes to the condition getting worse. Sleep studies show that people with fibromyalgia experience unusual wakefulness during deep sleep stages. They spend less time in slow-wave sleep, which is the phase when the body does its most critical tissue repair and the brain clears metabolic waste.
Without adequate deep sleep, the nervous system becomes more sensitive to pain the following day, which makes it harder to sleep the next night, which increases pain sensitivity further. This feedback loop is one reason fibromyalgia tends to be self-reinforcing once it takes hold.
Other Conditions That Raise the Risk
Living with another chronic pain or inflammatory condition increases the likelihood of developing fibromyalgia on top of it. About 12% of people with lupus also meet the criteria for fibromyalgia. Similar patterns show up in rheumatoid arthritis, osteoarthritis, and other autoimmune diseases. The constant pain signaling from these conditions may essentially train the nervous system into the sensitized state that defines fibromyalgia.
Roughly half of people diagnosed with fibromyalgia also show objective signs of small fiber neuropathy, a condition where the tiny nerve endings in the skin are damaged or reduced in number. A meta-analysis found the prevalence at 49%. This suggests that for a significant portion of patients, there is a measurable physical change in the peripheral nerves, not just altered brain processing. Whether the nerve damage causes the fibromyalgia or results from the same underlying process remains an open question.
How Fibromyalgia Gets Diagnosed
There’s no blood test or imaging scan for fibromyalgia. Diagnosis is based on a clinical assessment using criteria updated in 2016. To qualify, you need widespread pain in at least four of five body regions (left side, right side, upper body, lower body, and the spine/trunk area) that has persisted at a similar level for at least three months. Doctors also score the number of painful areas and the severity of associated symptoms like fatigue, unrefreshing sleep, and cognitive difficulties.
One important detail: a fibromyalgia diagnosis doesn’t rule out other conditions. You can have fibromyalgia alongside lupus, arthritis, or any other illness. This matters because people sometimes get told their pain is “just fibromyalgia” when something else also needs treatment.
Putting It Together
Fibromyalgia develops through a sequence, not a single moment. A person inherits genes that make their nervous system more susceptible to sensitization. At some point, a trigger (injury, infection, surgery, trauma, chronic illness, or sometimes nothing identifiable) pushes the nervous system past a tipping point. Chemical imbalances in the brain and spinal cord lock in the amplified pain response. Sleep disruption accelerates the process. Over time, the brain physically reorganizes around this new baseline, making the condition persistent.
No one “catches” fibromyalgia or brings it on themselves. It’s the result of biological processes that, once set in motion, change how the nervous system functions at a fundamental level.