Fibromyalgia doesn’t have a single cause. It results from a combination of nervous system changes, genetic predisposition, and environmental triggers that together amplify how the brain and spinal cord process pain signals. Roughly 2% to 8% of the global population lives with the condition, and women are seven to nine times more likely to develop it than men.
Central Sensitization: The Core Mechanism
The best-supported explanation for fibromyalgia centers on a process called central sensitization. In a healthy nervous system, the brain receives a pain signal, interprets it, and responds proportionally. In fibromyalgia, the central nervous system amplifies those signals, so stimuli that wouldn’t normally be painful (light pressure, moderate cold, mild exertion) register as pain. This isn’t imagined pain. It reflects measurable changes in brain and spinal cord chemistry.
People with fibromyalgia have roughly three times the normal concentration of substance P in their spinal fluid. Substance P is a chemical messenger that transmits pain signals. At the same time, levels of glutamate, the brain’s main excitatory chemical, are elevated both in spinal fluid and directly within brain tissue. These increases mean the volume knob on pain signaling is turned up far higher than it should be.
Meanwhile, the chemicals that normally dampen pain are running low. Serotonin, norepinephrine, and their related byproducts are all reduced in people with fibromyalgia. Serotonin helps regulate mood and pain perception. Norepinephrine helps the body suppress pain during stress. When both are depleted, the brain loses some of its built-in ability to filter out or quiet pain signals. The result is a nervous system that overreacts to input and struggles to turn itself back down.
Genetic Factors That Raise Risk
Fibromyalgia runs in families, and researchers have identified specific genetic variations that may explain part of that pattern. One of the most studied involves the COMT gene, which produces an enzyme responsible for breaking down stress-related chemicals like norepinephrine in the brain. A common variation in this gene (a substitution at a single spot in the DNA called codon 158) produces a version of the enzyme that works at only one-quarter of normal capacity.
People who inherit two copies of this low-activity variant end up with higher levels of norepinephrine in the prefrontal cortex, which can alter pain perception and stress response. In one study comparing fibromyalgia patients with rheumatoid arthritis patients and healthy controls, the low-activity genotype appeared exclusively in the fibromyalgia group. None of the fibromyalgia patients carried the fully functional version. This doesn’t mean the gene variant alone causes fibromyalgia, but it likely makes the nervous system more vulnerable to the kind of amplified pain processing that defines the condition.
What Triggers the Onset
Many people with fibromyalgia can trace the start of their symptoms to a specific event. Physical trauma is one of the most recognized triggers, particularly whiplash injuries from car accidents. Emotional trauma and prolonged psychological stress are also frequently reported as catalysts. The common thread seems to be any event that places the nervous system under extreme or sustained stress.
Infections can set the process in motion too. Hepatitis C, HIV, herpes viruses, and the bacterium that causes Lyme disease have all been linked to fibromyalgia onset. The idea isn’t that these infections cause fibromyalgia directly, but that the immune response and physiological stress of fighting them may push a genetically susceptible nervous system into a state of chronic sensitization.
Disrupted Sleep as Both Symptom and Driver
Sleep problems in fibromyalgia aren’t just a side effect. They may actively make the condition worse. A distinctive brain wave pattern called alpha-delta sleep is especially common in fibromyalgia patients. During normal deep sleep, the brain produces slow delta waves that allow tissue repair and restoration. In alpha-delta sleep, faster alpha waves intrude into this deep sleep phase, essentially preventing the brain from fully entering its most restorative state.
This matters because artificially inducing this same sleep disruption in healthy volunteers produces fibromyalgia-like symptoms, including widespread muscle pain and tenderness. That finding suggests disrupted sleep isn’t just a consequence of pain but can independently generate it. Poor sleep also reduces the body’s production of growth hormone, which is needed for tissue repair, creating a cycle where unrefreshing sleep leads to more pain, which leads to worse sleep.
Inflammation and Immune Changes
Fibromyalgia was long considered a non-inflammatory condition, but newer evidence complicates that view. Blood tests in fibromyalgia patients show significantly elevated levels of IL-6, an inflammatory signaling molecule. In one study, fibromyalgia patients had IL-6 concentrations roughly 17 times higher than healthy volunteers. Other inflammatory markers show altered levels as well, though the pattern is complex: some go up while others go down.
These immune changes don’t look like classic inflammation (there’s no joint swelling or tissue destruction as in rheumatoid arthritis), but they may contribute to the fatigue, cognitive fog, and pain sensitivity that define the condition. Whether the immune changes cause symptoms or result from them is still an open question, but the presence of measurable inflammatory shifts confirms that fibromyalgia involves real biological changes.
Nerve Damage in the Skin
About 50% of women with fibromyalgia have reduced density of small nerve fibers in the skin, as confirmed by a meta-analysis covering more than 900 patients. When skin biopsies are taken and examined under a microscope, significantly fewer of the tiny nerve endings that detect temperature and pain are present compared to healthy individuals. In one analysis, 63% of fibromyalgia patients showed this reduction, versus just 18% of healthy controls.
This finding is significant because it provides visible, physical evidence of nerve involvement in at least a large subset of patients. It doesn’t explain all fibromyalgia symptoms, and researchers caution that reduced nerve fiber density doesn’t automatically mean small fiber neuropathy is the root cause. But it does suggest that for many patients, the problem isn’t limited to the brain and spinal cord. The peripheral nerves themselves may be affected.
The Stress Response System
The body’s main stress response system, the hypothalamic-pituitary-adrenal (HPA) axis, also behaves differently in fibromyalgia. This system controls cortisol release, which helps regulate energy, immune function, and inflammation. Some fibromyalgia patients show slightly elevated cortisol throughout the day and reduced sensitivity in the feedback loop that normally tells the body to stop producing it.
Interestingly, these cortisol abnormalities appear to be most closely tied to depression rather than pain itself. Fibromyalgia patients without depression tend to have more normal cortisol patterns. This distinction matters because it suggests the HPA axis changes may drive the mood and fatigue components of fibromyalgia rather than the pain directly, adding another layer to what makes the condition so difficult to pin down to a single cause.
Why It’s Called a “Volume Control” Problem
The clearest way to understand fibromyalgia is as a disorder of pain regulation rather than pain generation. There is no damaged joint or inflamed tissue sending pain signals. Instead, the system that interprets and controls those signals has become miscalibrated. Too much substance P and glutamate amplify incoming signals. Too little serotonin and norepinephrine weaken the brain’s ability to suppress them. Disrupted sleep prevents recovery. Genetic variations make the system vulnerable in the first place. And a triggering event, whether physical, emotional, or infectious, can push the system past a tipping point.
This is why fibromyalgia affects so many body systems at once. Pain, fatigue, sleep disruption, cognitive difficulty, and mood changes all stem from a central nervous system that has lost its ability to properly filter and regulate sensory input. It also explains why the condition doesn’t show up on standard blood tests or imaging, since the problem lies in how the nervous system functions rather than in structural damage to any particular organ.