Central sensitization is real, and harder to pin down than claimed

You have hurt for two years: neck, shoulders, hips, sometimes your jaw. The scans show ordinary wear, the blood work is clean, and one clinician wonders aloud whether stress is the real problem. Then a physical therapist hands you a symptom questionnaire, scores it on the spot, and sends you home with a new phrase: central sensitization.

Both visits gave you something incomplete. The first ignored decades of research showing that the nervous system can amplify pain without fresh tissue damage, in ways that show up on brain scans and in laboratory tests. The second gave a questionnaire more authority than it has earned. In a 2026 study at an Israeli hospital pain clinic, a widely used central sensitization questionnaire caught 92% of the patients whose physicians had diagnosed the type of pain it is meant to detect. It also flagged more than half of the patients who did not have it.

So this article makes two corrections. Central sensitization is real nervous-system physiology, not a polite word for imagined pain. And it is harder to establish in any one person than a single score suggests.

A third kind of pain, named in 2017

For most of modern medicine, pain came in two kinds. Nociceptive pain comes from actual or threatened damage to body tissue, the ache of a sprain or an inflamed joint. Neuropathic pain comes from a lesion or disease in the nerves that carry sensation.

In 2017 the International Association for the Study of Pain (IASP), the reference body for pain definitions, adopted a third category, as Eva Kosek of the Karolinska Institutet recounts in a 2024 review. IASP calls it nociplastic pain: pain arising from altered nociception, the nervous system’s handling of danger signals, without clear evidence of tissue damage or nerve disease to account for it. The National Institute of Neurological Disorders and Stroke (NINDS) gives the plain-language version. It describes pain driven by altered processing inside the nervous system, with no clear injury or disease behind it, and it names fibromyalgia, irritable bowel syndrome (IBS) and chronic low back pain as examples.

Central sensitization is the leading proposed mechanism. IASP defines it as nerve cells in the brain and spinal cord responding more strongly than usual to ordinary input, or responding to input too weak to trigger them normally. Clinically, IASP notes, it can’t be observed directly; it can only be inferred from signs such as allodynia and hyperalgesia. Allodynia is pain from something that should not hurt, like a light touch. Hyperalgesia is more pain than expected from something that normally hurts a little.

The idea began in the laboratory. In a 2011 review in the journal Pain, Clifford J. Woolf of Harvard Medical School described it as a long-lasting but reversible rise in how excitable the pain pathways become, one researchers can produce quickly in healthy volunteers.

Three terms now travel together. A review published in October 2026 by anesthesiologists at Taiwan’s Chi Mei Medical Center sorts them this way: central sensitization is a mechanism, nociplastic pain is a descriptor of what a clinician observes, and chronic primary pain is a diagnostic category in the World Health Organization’s ICD-11 classification, which our guide to acute and chronic pain explains. In January 2026, Winfried Häuser and Kosek, two of the concept’s leading figures, warned in the European Journal of Pain against mixing these up, and added a sentence worth keeping: “Nociplastic pain is not a new term for pain of unknown origin.”

The brainstem circuits that normally dampen or boost pain signals, part of the same story, are covered in our explainer on how the nervous system produces pain.

The evidence that it happens in the nervous system

The first strong answer to it’s all in your head came from a brain scanner. In a 2002 study led by Richard H. Gracely at the National Institute of Dental and Craniofacial Research (NIDCR), researchers pressed on the thumbnails of 16 people with fibromyalgia and 16 matched volunteers during functional MRI. At the same moderate pressure, the patients showed greater activation than the volunteers in 13 brain regions. When the volunteers received enough pressure to hurt as much as the patients reported, their brain activity looked much like the patients’. The patients’ brains were registering real pain at a pressure that barely stirred anyone else’s.

Many imaging studies followed. A second line of evidence is stranger. In a 2024 review in the Annals of the Rheumatic Diseases, Daniel J. Clauw of the University of Michigan describes research in which people with fibromyalgia and related conditions were about as oversensitive to bright light and loud sound as they were to painful stimuli. Light and sound reach the brain through cranial nerves, skipping the spinal cord entirely. A heightened response to them, Clauw argues, can only originate in the central nervous system.

A 2024 review in Nature Reviews Neurology from Clauw’s Michigan group lists the symptoms that tend to come along: pain in several body regions, fatigue, disturbed sleep, trouble with thinking, depression and anxiety, often with tenderness all over and sensitivity to lights, odors and noises.

None of this says mood causes the pain. It says the system that produces pain, fatigue and sensory experience is working differently, which NINDS describes as one way some people develop chronic pain after an injury has healed.

A 2021 review in The Lancet, led by Mary-Ann Fitzcharles of McGill University, says this type of pain tends to respond less to treatments aimed at the body’s tissues, such as anti-inflammatory drugs, opioids, surgery and injections.

The 2021 criteria, and how far they have been tested

In 2021 an IASP group led by Kosek published the first clinical criteria for nociplastic pain, covering only pain in muscles, joints and bones. A clinician first needs pain that has lasted beyond three months and covers a region or several areas rather than one discrete spot. The examination has to find signs of heightened sensitivity where it hurts, and tissue damage or nerve injury cannot fully account for the pain. When all four hold, the pain counts as possible nociplastic pain.

The grade rises to probable with two additions. The person reports a history of hypersensitivity in the painful area, to touch, movement, pressure, heat or cold. And at least one related problem is present: sensitivity to sound, light or smells, sleep broken by frequent waking, fatigue, or trouble with thinking.

Three features matter to patients. Nociplastic pain can sit alongside other kinds; IASP’s own note says a person can have both nociceptive and nociplastic pain. The CSI, the questionnaire discussed below, is not part of them. And laboratory sensory testing is optional; Jo Nijs and colleagues at Vrije Universiteit Brussel acknowledged in a 2021 review that a full testing protocol is not yet realistic in ordinary clinics.

Field testing is early. A 2025 reliability study had two physical therapists apply them to 32 written case descriptions rather than real patients; agreement between the raters ranged from weak to perfect. In a 2026 paper in Pain, an IASP task force and an outside expert panel ranked clinical features, and the authors note there is still no consensus on how to assign a pain type to a real patient. Criteria for ordinary nociceptive pain, they add, have never been established. The October 2026 review judged the criteria acceptable in trained hands and uncertain in primary care.

Why a questionnaire score can’t settle it

Central sensitization, as IASP defines it, is a change in how nerve cells inside the brain and spinal cord respond, and those responses cannot be recorded directly in a living person. Nijs and colleagues, who champion the concept, say exactly that. IASP’s note adds that the term strictly applies only when a system’s input and output are both known, which is why clinicians infer it from signs.

A shortcut spread anyway. The Central Sensitization Inventory (CSI), developed by a Dallas team and first published online in 2011, asks about pain alongside sleep, concentration, sensitivity to light and smells, stress and other symptoms. In its original validation, all four of its underlying factors related to bodily and emotional symptoms, and people with fibromyalgia scored highest.

A 2023 meta-analysis in Pain, from the University of Reading in England and Queen’s University in Ontario, pooled 66 studies with 13,284 participants. CSI scores correlated strongly with depression, anxiety, stress, catastrophizing (a habit of dwelling on and magnifying pain), poor sleep and fear of movement. They correlated weakly or not at all with laboratory measures such as pain thresholds and the way pain builds with repeated stimulation. The authors’ conclusion was blunt: “The CSI more closely reflects psychological hypervigilance than increased responsiveness of nociceptive neurons.”

A 2024 meta-analysis led by Randy Neblett of the PRIDE Research Foundation in Dallas, one of the CSI’s developers, read the evidence more favorably. Across 33 studies, CSI scores correlated significantly with all five laboratory tests examined, most clearly with pressure pain thresholds. The two reviews pooled different studies and weigh the laboratory link differently. Even on the kinder reading, the score’s strong ties to depression, anxiety and sleep mean a high result cannot be taken as nerve sensitivity alone, an overlap our article on physical and psychological contributors to persistent symptoms picks up.

The 2026 Israeli study, from Rambam Health Care Campus in Haifa, compared questionnaire results for 89 patients with physicians’ diagnoses based on ICD-11. Physicians judged 28% to have nociplastic pain, and a third had two or more pain mechanisms at once. The CSI caught 92% of the nociplastic cases but correctly cleared only 45% of the patients without it. The American College of Rheumatology’s 2016 fibromyalgia criteria were better balanced, at 88% and 69%. Even the questionnaire’s supporters agree on its limits: Nijs and colleagues write that the CSI assesses symptoms and was never meant to diagnose central sensitization by itself.

A purpose-built alternative is arriving. In The Clinical Journal of Pain this October, researchers from the VA San Diego Healthcare System and several universities described a 16-item nociplastic pain questionnaire tested in 888 people. It told presumed nociplastic conditions apart from others with an accuracy score of 0.73 to 0.75, on a measure where 0.5 is a coin toss and 1.0 is perfect; its authors call it promising and say its clinical usefulness still needs study.

On this library’s five-verdict scale, diagnosing central sensitization from a CSI score alone sits at tested and not supported.

Cause, consequence, or both

If sensitization causes chronic pain, people who are more sensitive before any pain begins should be likelier to develop it. The OPPERA study, a US cohort funded by the National Institutes of Health, tested this with temporomandibular disorder (TMD), pain in the jaw joint and chewing muscles. Researchers measured pain sensitivity in 2,737 people without TMD and followed them for up to 5.2 years; 260 developed it. Only 14 of 39 sensitivity measures predicted who did, and the authors called their contribution modest. The same team’s earlier comparison of people who already had chronic TMD had found a larger set of differences, which they described as profound.

That gap suggests the arrow points both ways. Some sensitivity may come before pain, and more builds once pain persists. Clauw’s review describes a similar sequence in studies of children with new nociplastic pain: sleep and memory problems tended to appear first, then pain, then mood problems, and a mood disorder at the start did not predict later pain.

Clauw also sketches two broad routes in. Some people seem to carry a nervous system primed for this from early life, often with sleep or memory trouble in adolescence followed by pain in one region after another. Others develop it on top of an identifiable source of pain, such as arthritis, and for them treating that source often helps. His review puts women at 1.5 to 2 times the risk of men, a difference that emerges after puberty.

So the label should never close the question of a physical cause. Clauw stresses that a nociplastic diagnosis does not mean peripheral sources of pain are absent or can be left untreated. The October 2026 review warns that an overly broad label can hide disease nobody has found yet. And in the Haifa clinic, one patient in three had more than one mechanism.

For the claim that central sensitization contributes to some people’s chronic pain, the library’s verdict is positive evidence with a contested interpretation: the physiology is measurable in groups, while its role as cause or consequence in any one person is unsettled.

Where the label is proposed, fibromyalgia included

Nijs’s 2021 review reports signs of central sensitization in a meaningful subgroup of people with conditions as varied as fibromyalgia, IBS, migraine, osteoarthritis, rheumatoid arthritis, whiplash and low back pain, and says it appears less common in tendon problems and shoulder pain.

Federal health pages describe the pattern without always using the term. NIDCR, in a page reviewed in September 2026, says TMD affects about 5% of US adults and is roughly twice as common in women, especially those 35 to 44. Most cases have no clear cause, and research points to genetics, psychological and life stressors, and how a person perceives pain. TMD often occurs with headaches, back pain, sleep problems, IBS and fibromyalgia, and NIDCR says research does not support a bad bite or braces as causes. The National Institute of Diabetes and Digestive and Kidney Diseases describes IBS as a problem of brain-gut interaction in which some people feel pain from a normal amount of gas or stool, though that page was last reviewed in 2017.

Fibromyalgia is usually called the prototype, yet even here experts hedge. Häuser and Kosek’s 2026 summary says fibromyalgia is not always a pure nociplastic condition. Its criteria, course and treatment are reserved for our upcoming fibromyalgia entry.

What the label means for care, and questions to ask

No guideline yet matches treatment to pain mechanism; Kosek wrote in 2024 that such guidelines still need to be developed, and reviews by her and by Clauw caution against opioids for this kind of pain, though any medicine decision belongs to the prescriber. Graded activity, pacing, psychological pain therapies (the pain reprocessing therapy trial among them) and physical therapy are weighed one at a time in the treatment entries that follow.

When a clinician uses the term with you, these questions turn a label into information:

• What did the exam find, and where? Under IASP’s criteria, the label rests on signs of heightened sensitivity in the painful area, not on a form.
• Possible or probable? The criteria grade likelihood, so the grade tells you how firm the conclusion is.
• How much did a questionnaire count? A high CSI score reflects distress and sleep at least as much as nerve sensitivity.
• What else is contributing? Ask whether arthritis, a gut condition, nerve damage or another source of pain is also present and still needs its own treatment.
• What went into my chart? The same pain may be recorded as nociplastic pain, central sensitization, fibromyalgia or chronic primary pain. A 2026 Vanderbilt study of health records found clinicians most often wrote central pain syndrome, a term not intended for this kind of pain.
• What would make you look again? A good answer names the changes that would reopen the workup.

Signs that need attention sooner

A sensitization label covers the pain already assessed; a change in where or how you hurt deserves its own look. For back pain, the American Academy of Orthopaedic Surgeons says weakness in the legs or losing control of bladder and bowels needs medical attention right away, and back pain that comes with fever, chills or weight loss you can’t explain warrants a call to a doctor. Possible stroke signs, which the Centers for Disease Control and Prevention says call for 911 right away, include sudden numbness or weakness, particularly on one side of the body, sudden confusion, trouble speaking, and sudden trouble seeing. If long-running pain has pushed you toward thoughts of suicide, you can call or text 988 to reach the 988 Suicide & Crisis Lifeline, which is free, confidential and open around the clock.

The most useful thing to know

Central sensitization describes something real: a nervous system more responsive than it should be, with effects visible in brain scans, sensory tests and daily life. In any one person, though, it is an inference drawn from an examination and a history, using criteria only five years old and still being field-tested.

Hold both halves. If someone dismisses your pain because a scan looks clean, the science is on your side. If someone diagnoses it from a questionnaire alone, the same science gives you a fair question to ask back: what did the examination find?

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