What is Chronic Pain?

ICP – INSTITUTE FOR CHRONIC PAIN Link to Original Article: http://www.instituteforchronicpain.org/understanding-chronic-pain/what-is-chronic-pain

Patients and healthcare providers commonly think of pain as a symptom of an underlying injury or illness. Say, for example, you hurt your low back while lifting. Perhaps, you’ve injured a muscle or ligament, or perhaps it’s an injury to the spine, like a disc bulge or herniation. Either way, you now have pain and the pain is the symptom of the injury. The same might be true for any health condition that causes pain, particularly when it first starts.

Acute pain defined

We call this type of pain acute pain.  Acute pain has two characteristics. First, just as described, acute pain is a symptom of an underlying health condition. Second, its duration is relatively short.  Most injuries and illnesses heal within weeks. Some, however, take longer. As a rule of thumb, healthcare providers use a time frame of pain lasting less than six months.

Chronic pain is not long-lasting acute pain

Sometimes pain doesn’t go away. It can last for longer than six months. In fact, it can last for years. In these situations, there is a tendency among patients and some healthcare providers to continue to see the pain as a symptom of the underlying health condition that started it. They think of chronic pain as simply the long-lasting pain of an injury or illness that hasn’t yet healed.

This line of thinking leads to getting a lot of healthcare. Surgeries, injections, and narcotic pain medications are common attempts to reduce pain by focusing on the underlying condition that started the pain. The typical chronic pain patient has had any number of such procedures and therapies.

These procedures and therapies aren’t very effective. At best, they tend to provide temporary reductions in pain. Studies of healthcare expenditures show that in the last twenty years the rates of pain-related surgeries, injections and narcotic pain medications are at an all time high. At the same time, applications for pain-related disability are also at an all time high.1 Obviously, these procedures and therapies don’t work so well.

The truth is, once pain is chronic, it’s pretty hard to stop, particularly if the focus of care is to try to fix the underlying injury or illness that started it all.

The reason is that chronic pain is something more than the pain of a health condition that hasn’t healed. The importance of this point is hard to underestimate.

Chronic pain defined

Chronic pain has two characteristics that are different than acute pain. First, chronic pain lasts longer than six months. Second, and most importantly, chronic pain is pain that occurs in addition to the pain of the original health condition. In fact, the original, underlying condition may or may not have healed. It doesn’t really matter. Chronic pain is pain that has become independent of the underlying injury or illness that started it all.

Once pain has become chronic, attempts to fix the underlying injury or illness that started it tend to fail to reduce pain. The mistake that patients and some healthcare providers make is to think that chronic pain is just a long-lasting version of acute pain. However, chronic pain is pain that has taken on a life of its own. Chronic pain is pain that is occurring over and above the pain of the underlying injury or illness that started it all. As such, attempts to cure the original health condition commonly miss the mark.

Cause of chronic pain

What then is the cause of chronic pain? To answer this question, we need to understand some facts about the nervous system.

Whatever its initial cause, pain is a function of the nervous system. Say you injure your low back. Nerves around the site of the injury detect it and sends signals that travel on a highway of nerves from the injury to the spinal cord and up to the brain. Once they get to the brain, the brain processes the signals and they register as pain in the low back. The whole highway, from the nerves in the low back to the brain, is the nervous system.

At the same time as the signals travel from the injury to the brain, the whole nervous system becomes reactive. Like a fire detector in a building sounding the alarm in response to fire, the nervous system sets off the alarm bells when in pain. Our muscles become tense. We guard and grimace. We cry and are emotionally alarmed. The nervous system controls all these reactions. We can think of it as the whole nervous system going into ‘red alert.’

This reactivity of the nervous system is all well and good when it comes to acute pain. It helps us to know that something is wrong. Becoming alarmed, we protect against further injury and seek help. Once the original injury or illness heals, everything about the nervous system comes back to normal.

In some people, the nervous system can stay in a persistent state of reactivity even upon healing of the original acute injury or illness. The whole nervous system becomes more and more reactive in a process called wind-up. This reactivity of the nervous system comes to maintain pain in a vicious cycle, over and above the pain of the original condition that started it all. The end state of this process is a highly reactive nervous system called central sensitization.

The hallmarks of central sensitization are increasingly widespread pain and increasingly intense pain. Suppose you have an injury to your neck and come to have chronic neck pain. Once central sensitization sets in, you also develop pain in your shoulders and upper back as well as tension headaches. Additionally, the pain becomes so intense that even touch can hurt.

Other problems occur as well with central sensitization. Since the nervous system also controls our emotional lives, a highly reactive nervous system leads to anxiety and irritability, poor sleep, fatigue, and eventually depression. These psychological problems are secondarily stressful. The stress adds to the reactivity of the nervous system, making the pain worse. Another vicious cycle results.

The upshot of it all is that chronic pain is pain causing pain by way of central sensitization.

Central sensitization can occur with all pain conditions. It can occur with spine-related acute injuries, whiplash injuries, fibromyalgia, chronic tension headaches, migraine headaches, rheumatoid arthritis, osteoarthritis, complex regional pain syndromes, and endometriosis. It can occur with injuries from a motor vehicle accident or following surgeries.

The importance of treating the nervous system in chronic pain

Chronic pain is thus categorically different from acute pain. It’s not just that it lasts longer. It’s that the whole nervous system is involved, maintaining the chronicity of the pain, over and above whatever pain that might continue, if any, from the original health condition that started it.

Earlier, we commented on the frequent failure of surgeries, injections, and narcotic pain medications to permanently reduce pain. From here, we can see why. They are attempts to fix the injury or condition that started it all. The original condition, however, is typically not what’s responsible for maintaining the pain in a chronic cycle. That is to say, the treatments fail because none of them address the most important cause of chronic pain – central sensitization.

The only treatment that fully addresses central sensitization is chronic pain rehabilitation.


1. Brook, M. I., Deyo, R. A., Mirza, S. K., Turner, J. A., Comstock, B. A., Hollingworth, W., & Sullivan S. D. (2008). Expenditures and health status among adults with back and neck problems. Journal of the American Medical Association, 299, 656-664.

Date of publication: April 27, 2012

Date of last modification: October 23, 2015

Murray J. McAllister, PsyD

Murray J. McAllister, PsyD, is the editor and founder of the Institute for Chronic Pain (ICP). The ICP is an educational and public policy think tank. Its mission is to lead the field in making pain management more empirically supported. Additionally, the ICP provides Academic quality information on chronic pain that is approachable to patients and their families. Dr. McAllister is also the clinical director of pain services for Courage Kenny Rehabilitation Institute (CKRI), part of Allina Health, in Minneapolis, MN. Among other services, CKRI provides chronic pain rehabilitation services on a residential and outpatient basis.

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