Chronic pain is more than an injury that never healed

You tweak your back hauling a couch up the stairs. For the first few weeks you count days, the way you would with a sprained ankle, expecting each morning to be a little easier than the last. Then the count passes three months. The soreness has changed character, and nobody can point to anything still torn.

That moment, when pain outlasts the injury that started it, is more common than most people assume. In a national survey that followed more than 10,000 American adults from 2019 to 2020, new chronic pain appeared among previously pain-free people at a rate of 52.4 cases per 1,000 person-years. The researchers set that beside published US rates for new diabetes, depression and high blood pressure, and pain came out ahead of all three.

Crossing that line also changes what the pain is called. Under the international disease classification adopted in 2019, pain that persists or recurs beyond three months is chronic, and sometimes it counts as a condition in its own right rather than a leftover symptom. That does not make it permanent. In the same survey, about one in ten adults with chronic pain was pain-free a year later.

Where the three-month line comes from

Start with pain itself. The International Association for the Study of Pain (IASP), the field’s main professional body, defines it as an unpleasant sensory and emotional experience tied to actual or potential tissue damage, or resembling an experience that is. That wording comes from a 2020 revision, the first change to the definition since the IASP Council adopted it in 1979, and it says nothing about time. How the nervous system turns raw signals into that experience is the subject of our companion piece on pain processing.

Time enters through federal plain-language pages. The National Institute of Neurological Disorders and Stroke (NINDS) describes acute pain as pain that begins suddenly and ends once its cause is treated or healed. It calls pain chronic when it lasts beyond three months or beyond the expected healing time, and MedlinePlus, from the National Library of Medicine, draws the same double line. That or matters, because a badly broken leg can take longer than three months to mend.

The formal rule comes from a classification an IASP working group built with the World Health Organization for ICD-11, the 11th revision of the International Classification of Diseases. Chronic pain is pain that persists or recurs for more than three months. Recurs is the quiet word: pain that comes and goes for months can qualify.

The classification then splits chronic pain in two:

• Chronic secondary pain sits on top of another identifiable problem: musculoskeletal disease, nerve damage, cancer, an operation or injury, a disorder of the internal organs, or a headache or facial pain condition. Here the pain is, at least at first, treated as a symptom of that problem.
• Chronic primary pain is a diagnosis in itself. It applies when pain has lasted more than three months, comes with significant emotional distress or loss of function, and is not better explained by another condition.

“In conditions such as fibromyalgia or nonspecific low-back pain, chronic pain may be conceived as a disease in its own right…,” the IASP working group wrote in the journal Pain in 2019. Its companion paper adds that the diagnosis can be made whether or not a biological or psychological contributor has been identified, unlike the approach taken in ICD-10 and the DSM-5 psychiatric manual.

That corrects the most widespread belief about chronic pain: that it is simply an injury that has not finished healing. Sometimes it is. But NINDS notes that chronic pain can begin without a known cause and can continue after an injury has resolved. Pain without visible damage is not pain without a cause, and it is not imaginary. One proposed explanation, a nervous system that has turned up its own sensitivity, gets a full treatment in our article on central sensitization.

One catch for American readers. ICD-11 was adopted by the 72nd World Health Assembly in 2019 and took effect internationally on January 1, 2022, but the United States still codes diagnoses with ICD-10-CM, in use since October 1, 2015. In April 2024 the National Committee on Vital and Health Statistics, which advises the Secretary of Health and Human Services, urged the department to name one office to lead the move to ICD-11, without setting a date. So chronic primary pain is an international diagnosis that US billing codes do not yet carry.

The middle zone nobody agrees on

Between one month and three, the labels get slippery. The Centers for Disease Control and Prevention’s 2022 clinical practice guideline on prescribing opioids for pain uses three bins: acute pain lasts under a month, subacute pain lasts one to three months, and chronic pain lasts longer than three months.

The physical therapy profession went the other way. When the Academy of Orthopaedic Physical Therapy of the American Physical Therapy Association revised its low back pain guideline in 2021, it dropped the subacute group its 2012 version had used. The committee’s stated reason was that no accepted standard exists for defining subacute pain. Only acute and chronic remain.

The two bodies are not at odds: CDC’s bins organize medication decisions, while the physical therapy guideline sorts clinical trials. National statistics use a third test, counting pain as chronic if it occurred on most days or every day over the past three months. That measures frequency, not healing.

Duration labels, in other words, are tools built for particular jobs, not lines drawn in your biology. Pain on day 89 is no different from pain on day 91. Crossing a line should prompt a fresh look, nothing more.

One in four adults, and not only older ones

Survey data from 2023 show how many people live past that line. In a brief the National Center for Health Statistics (NCHS) released in November 2024, 24.3% of US adults had chronic pain. Another measure, high-impact chronic pain, covers pain that limited life or work activities on most days or every day; 8.5% of adults had it, roughly a third of everyone with chronic pain.

The breakdown corrects two assumptions at once:

Group (2023)	Chronic pain	High-impact chronic pain
Ages 18 to 29	12.3%	3.0%
Ages 30 to 44	18.3%	4.9%
Ages 45 to 64	28.7%	11.3%
Ages 65 and older	36.0%	13.5%
Large central metro areas	20.5%	7.3%
Nonmetropolitan areas	31.4%	11.5%

Chronic pain climbs with age, yet about one in eight adults under 30 reported it. Rates outside metropolitan areas far exceeded those in big cities. Women’s rate was somewhat higher than men’s, 25.4% against 23.2%, a gap the brief marks as statistically significant.

The brief also prints 2019 figures of 20.4% and 7.4%, but it does not test whether the change is real, so treat it as a hint rather than a proven rise. The widely repeated figure of 50 million Americans traces to a CDC analysis of 2016 survey data: 20.4% of adults, or 50.0 million people. A figure of 100 million also circulates. It comes from a 2012 Johns Hopkins-led study in The Journal of Pain that used a different federal survey and counted joint pain and arthritis too. That study put the yearly cost of pain at $560 billion to $635 billion in 2010 dollars, counting extra health care spending and lost productivity. By the authors’ comparison, that topped the annual cost of heart disease, cancer or diabetes taken one at a time.

How often pain turns chronic, and how often it lets go

A snapshot cannot show how often new cases begin or old ones end. For that, a team led by Richard L. Nahin of the National Center for Complementary and Integrative Health, an institute of the National Institutes of Health (NIH), tracked 10,415 adults who answered the national survey in both 2019 and 2020. The results appeared in JAMA Network Open in 2023.

• New cases are common. Among adults with no pain in 2019, 6.3% had chronic pain a year later. Expressed as a rate that accounts for how long each person was followed, that is 52.4 new cases per 1,000 person-years. “In this cohort study, the incidence of chronic pain was high compared with other chronic diseases,” the NIH-led team wrote, setting it beside published US rates of 7.1 for diabetes, 15.9 for depression and 45.3 for high blood pressure. Those comparison rates come from other studies, so they give scale, not an exact ranking.
• Occasional pain is a warning light. Of people who had pain on some days in 2019, 14.9% had moved up to chronic pain by 2020.
• Chronic pain is not a one-way door. Of those with chronic pain in 2019, 61.4% still had it a year later. But 10.4% were completely pain-free, and most of the rest had dropped back to pain on only some days.
• Age mattered; sex did not. Adults 50 and older had higher rates of both new and persisting chronic pain. Men and women developed new chronic pain at similar rates, even though women are somewhat more likely to be living with it at any given time.

The authors flag limits: no information on what caused anyone’s pain, only two points in time, and possible under-counting of people whose new pain kept them from answering again.

Back pain: the clearest US measurement

The best American measurement of the acute-to-chronic shift in a single condition comes from low back pain. A University of Pittsburgh-led study that appeared in JAMA Network Open in 2021 enrolled 5,233 adults who sought care for new low back pain at 77 primary care practices in four US regions. Six months later, 32% met the NIH research task force’s definition of chronic low back pain.

Several factors went with higher odds of that transition: a high-risk score on a short screening questionnaire, obesity, smoking, severe disability at the first visit, and a diagnosis of depression or anxiety. So did receiving opioids, imaging or a specialist referral in the first 21 days, care the authors classed as not following guidelines. That last finding is an association. Patients with worse pain may simply have received more of that care, so the study does not show that a scan or a prescription made anyone’s pain persist.

The companion TARGET trial tested a program that steered high-risk patients toward psychologically informed physical therapy. At six months, 47% of high-risk patients in program clinics and 51% in usual-care clinics had chronic back pain, a difference that could easily have been chance. About half crossed the line either way. Why pain persists in some people and not others is taken up in our piece on physical and psychological contributors; back pain and its treatment get their own entry.

After surgery

A 2006 review in The Lancet estimated that persistent pain follows 10% to 50% of common operations, including groin hernia repair, breast and chest surgery, leg amputation and coronary bypass, and is severe in roughly 2% to 10% of those patients. A 2019 Lancet review put chronic postsurgical pain at about 10% of surgical patients overall. Both point to the same early signal: pain after the operation that is intense or hard to control.

Nobody can yet predict reliably who will cross over. A multisite US study, Acute to Chronic Pain Signatures, is collecting brain imaging, molecular screening, sensory tests and questionnaires around knee replacement and chest surgery to see which combination forecasts pain six months later. Its 2022 protocol paper reports no results yet.

What each label changes in care

A label earns its keep only if it changes what happens next. Here is what each one tends to set in motion, and the question it hands to you and your clinician.

• Acute (under one month, in CDC’s scheme). The working assumption is that a cause is healing or being treated. CDC’s 2022 guideline says nonopioid therapies are at least as effective as opioids for many common acute pains and tells clinicians to make full use of nondrug and nonopioid options. CDC rates this category B (different choices suit different patients) on type 3 evidence (limited confidence). The question it raises: is recovery on the timeline expected for this injury?
• Subacute (one to three months, CDC only). CDC groups this stage with chronic pain and says nonopioid therapies are preferred for both, rated category A (applies to most patients) on type 2 evidence (true effect likely close to the estimate). The question: has the pain changed in character, location or intensity?
• Chronic (more than three months, or past expected healing). CDC’s preference continues, and the guideline warns against applying its advice as an inflexible standard. A Department of Health and Human Services task force, convened under the 2016 Comprehensive Addiction and Recovery Act, reported in 2019 that pain care should be individualized and multidisciplinary, drawing on medication, restorative therapies, interventional procedures, behavioral health approaches, and complementary and integrative health. That report is advisory, not a graded guideline. The question: is the original explanation still right, or does the pain now need assessing as a problem in itself?
• High-impact. Federal surveys add this tag when pain limits life or work most days. The question: which activities matter most to regain?
• Chronic primary pain (international only). Under ICD-11 this label means the pain, with its distress or disability, is itself the condition under care. The question: has another condition been reasonably considered and ruled out as the explanation?

The specific approaches, from graded activity and pacing to psychological pain-management strategies, physical therapy and acupuncture, each get a full evidence review in the library’s treatment series. Any decision about opioids or other pain medicines belongs to the prescriber. CDC’s guideline covers adult outpatients and does not apply to pain from sickle cell disease or cancer, to palliative or end-of-life care, or to people in hospital.

Signs that need prompt attention at any stage

A duration label says how long pain has lasted, not whether it is dangerous. Some features need medical attention whether the pain began yesterday or years ago.

Call 911. CDC lists the major warning signs of a heart attack as chest pain or discomfort; pain or discomfort in the jaw, neck, back, or one or both arms or shoulders; shortness of breath; and feeling weak, light-headed or faint. CDC’s instruction is to call 911 immediately if you notice these in yourself or someone else. New pain in those places does not belong on a three-month clock.

Back pain as an example of red flags. The American Academy of Orthopaedic Surgeons says weakness in the legs or loss of bladder and bowel control calls for medical attention right away. It advises contacting a doctor when back pain comes with fever, chills or unexpected weight loss, or does not improve within a few weeks. It lists a history of cancer, vascular disease, and pain that never lets up whatever your position or activity as reasons to see your primary care doctor. The American Association of Neurological Surgeons adds numbness or tingling, and pain that follows a recent injury.

Name the decision. Once pain has outlasted the expected healing time, whether it needs a new evaluation, a referral or a different plan is a question for the clinician treating it. Any change to pain medicine is a conversation with the person who prescribed it. And if long-lasting pain has worn you down to thoughts of suicide or self-harm, you can call or text 988 to reach the 988 Suicide & Crisis Lifeline at any hour.

The most useful thing to know

Crossing three months changes which questions matter; it does not settle how things turn out. Before that point, the main question is whether healing is on schedule. After it, the questions widen to what keeps the pain going and what would help you function. Chronic pain is common, it can be a condition in its own right, and it does not always last. In the national follow-up, close to four in ten adults with chronic pain no longer met the survey’s definition a year later, and about one in ten was free of pain entirely.

If your pain is nearing or past that mark, the most useful thing to carry into the exam room is a short written timeline: when it started, what set it off, how it has changed, what makes it better or worse, and what it is stopping you from doing. Every label in this article is built from that information.

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