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How Pain Works, Part II – Acute vs. Chronic

As you learn more about how pain works, you’ll notice a distinction is made between ‘acute’ and ‘chronic’ pain.

What does this mean? Is it just a matter of time?

Or is there something different happening when pain persists?

It turns out to be a bit more complicated than once thought… let’s discuss!

Acute vs. Chronic – Definitions

In medicine, acute refers to an illness that’s new or has a sudden onset – like a broken bone. Chronic refers to an illness that’s long lasting, or develops slowly over time – like osteoarthritis.

Acute could also refer to a symptom of chronic disease – for example, someone with arthritis could experience acute pain when bending their knee too far. In this case, the pain was acute (because it was sudden), but osteoarthritis is a chronic illness.

Acute Pain

Acute pain is new and sudden pain, such as that which is experienced with an injury. There are countless examples, many of which happen on a daily basis: stubbing your toe, pinching your skin, etc. Typically, once the painful stimulus is removed, or the injury has healed, acute pain goes away. Acute pain is normal, and useful in helping us avoid harm!

Chronic Pain – Time

Chronic pain is usually defined as pain that lasts longer than expected healing times. Therefore, pain lasting more than three to six months is usually defined as ‘chronic’, since most injuries heal within that time frame. 1,2

When pain lasts longer than expected, we know something is up.

But what’s up? Is the injury not healing? Is the illness not going away?

Chronic Pain – Mechanisms

Pain can persist for a few reasons – reasons that begin in the acute phase. For this reason,  simply defining chronic pain by how long it lasts may be missing the boat!

Of course, chronic pain may be due to a chronic disease. 2 In this case, the chronic disease causes the symptom of pain. Common examples include diseases/conditions such as nerve root impingement, rheumatoid arthritis, and cancer. It is important that chronic pain is properly investigated to identify such conditions.

However, pain may also persist with no identifiable underlying disease!

In these cases, the persistent pain is due to changes in how pain is processed by the nervous system. 1,2 Signals may be detected and sent more easily, and perceived as more dangerous by the brain (whether you agree with it or not!). We’ll make sense of how these changes occur in future articles.

These new pain mechanisms can overlap with an underlying condition, complicating the overall picture. 2,3 Or, they can be completely independent – having no relationship with disease or injury at all! The original problem is gone, but the pain persists!


Chronic pain isn’t just pain that lasts a long time. When pain persists, the nervous system actually changes how it processes pain (becoming better at it, for better or for worse!). 1

No matter what the apparent cause of pain, these changes still occur, contributing to the overall experience of pain. 3 In fact, chronic pain can be thought of as the problem or illness itself! 2

Furthermore, these changes can start early during the acute phase. This is another reason why it’s important to study – it may help us prevent pain from becoming chronic!

Don’t let any of this scare you. While the nervous system can be sensitized, it can also be de-sensitized. Even the most complicated pain can be reduced and perhaps extinguished! And one of the first and most important steps is to learn how pain works.

Stay tuned for more!


ResearchBlogging.org1. Apkarian AV, Baliki MN, & Geha PY (2009). Towards a theory of chronic pain. Progress in neurobiology, 87 (2), 81-97 PMID: 18952143

2. Bonezzi C, Demartini L, & Buonocore M (2012). Chronic pain: not only a matter of time. Minerva anestesiologica, 78 (6), 704-11 PMID: 22467050

3.Finan PH, Buenaver LF, Bounds SC, Hussain S, Park RJ, Haque UJ, Campbell CM, Haythornthwaite JA, Edwards RR, & Smith MT (2012). Quantitative sensory tests of central sensitization are associated with discordance between pain and radiographic severity in knee osteoarthritis. Arthritis and rheumatism PMID: 22961435

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    2 Responses to How Pain Works, Part II – Acute vs. Chronic

    1. kathy says:

      I would love to know how to break the cycle!
      I think that for me , fear has become large part of the chronic on-going nature and the worsening of pain.
      As each medical intervention is wrong for me and or fails , fear goes up..
      We need to break the pain/anxiety/ more pain cycle.
      but its tough when one is in all consuming pain..
      How can we break free?

      • Tony Ingram says:

        Hi Kathy!

        How to break free? That’s the million dollar question isn’t it! Learning about pain to break the fear cycle and learn to cope is definitely a good start. You’re so right about the fear cycle. I wrote about it before here: Outdated Pain Theories, Conclusion – “What’s the harm?”. What’s really sad is that most of these unhelpful, harmful beliefs are based on erroneous information. Check out those ‘outdated pain theories‘ articles, hopefully you’ll find them reassuring!

        Hang in there!


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