Classification of Chronic Pain – IASP Pain Terminology

IASP Pain Terminology – IASP – Dec 2017

The following pain terminology is updated from “Part III: Pain Terms, A Current List with Definitions and Notes on Usage” (pp 209-214) Classification of Chronic Pain, Second Edition, IASP Task Force on Taxonomy, edited by H. Merskey and N. Bogduk, IASP Press, Seattle, ©1994.

This “dictionary” is not new, but these terms are still used and pain is no different than it was years ago.

I’m posting this because it makes the subtle distinctions clear between often misused words: allodynia and the latest fashionable, yet hypothetical syndrome of “hyperalgesia”, when pain supposedly worsens due to “too much” opioid medication. 













         Interdisciplinary Treatment*

Multidisciplinary Treatment*

Multimodal Treatment*



Neuropathic Pain*

Central Neuropathic Pain

Peripheral Neuropathic Pain*



Nociceptive Neuron*

Nociceptive Pain*

     Nociceptive Stimulus*


Nociplastic Pain*

Noxious Stimulus 

Pain Threshold*

Pain Tolerance Level*



Central Sensitization*

Peripheral Sensitization*

Unimodal Treatment*

Note: An asterisk (*) indicates that the term is either newly introduced or the definition or accompanying note has been revised since the 1994 publication.


Pain due to a stimulus that does not normally provoke pain.

Note: The stimulus leads to an unexpectedly painful response. This is a clinical term that does not imply a mechanism.

Allodynia may be seen after different types of somatosensory stimuli applied to many different tissues.

The term allodynia was originally introduced to separate from hyperalgesia and hyperesthesia, the conditions seen in patients with lesions of the nervous system where touch, light pressure, or moderate cold or warmth evoke pain when applied to apparently normal skin. 

It is important to recognize that allodynia involves a change in the quality of a sensation, whether tactile, thermal, or of any other sort. 

The original modality is normally nonpainful, but the response is painful. 

There is thus a loss of specificity of a sensory modality.

By contrast, hyperalgesia (q.v.) represents an augmented response in a specific mode, viz., pain. 

With other cutaneous modalities, hyperesthesia is the term which corresponds to hyperalgesia, and as with hyperalgesia, the quality is not altered. 

In allodynia, the stimulus mode and the response mode differ, unlike the situation with hyperalgesia.

This distinction should not be confused by the fact that allodynia and hyperalgesia can be plotted with overlap along the same continuum of physical intensity in certain circumstances, for example, with pressure or temperature.


Increased pain from a stimulus that normally provokes pain.

Note: Hyperalgesia reflects increased pain on suprathreshold stimulation.

This is a clinical term that does not imply a mechanism.

Yet, whenever I see this term used they are referring to the “mechanism” of taking opioids, claiming that the opioids themselves are the mechanism causing our pain.

For pain evoked by stimuli that usually are not painful, the term allodynia is preferred, while hyperalgesia is more appropriately used for cases with an increased response at a normal threshold, or at an increased threshold, e.g., in patients with neuropathy.

It should also be recognized that with allodynia the stimulus and the response are in different modes, whereas with hyperalgesia they are in the same mode.

Current evidence suggests that hyperalgesia is a consequence of perturbation of the nociceptive system with peripheral or central sensitization, or both, but it is important to distinguish between the clinical phenomena, which this definition emphasizes, and the interpretation, which may well change as knowledge advances.

Hyperalgesia may be seen after different types of somatosensory stimulation applied to different tissues.


A painful syndrome characterized by an abnormally painful reaction to a stimulus, especially a repetitive stimulus, as well as an increased threshold.

Note: It may occur with allodynia, hyperesthesia, hyperalgesia, or dysesthesia.

  • Faulty identification and localization of the stimulus,
  • delay,
  • radiating sensation, and
  • aftersensation

may be present, and the pain is often explosive in character.


Diminished pain in response to a normally painful stimulus.

Note: Hypoalgesia was formerly defined as diminished sensitivity to noxious stimulation, making it a particular case of hypoesthesia (q.v.). However, it now refers only to the occurrence of relatively less pain in response to stimulation that produces pain. Hypoesthesia covers the case of diminished sensitivity to stimulation that is normally painful.

Most people, even doctors and researchers, don’t use all these terms correctly, and the term hyperalgesia is regularly abused.

I see it used liberally in the media without mention that hyperalgesia has never been proven to exist in humans, only lab rats, which are certainly not a valid model for the supposedly biopsychosocial syndrome of chronic pain.

When the objective is to vilify opioids or those that need them, we are caught in a no-win situation:

  • First, we are chastised for our use of opioids and told we should not take opioids expecting to reduce our pain to zero.
  • Then, if we still have any pain, terms like “hyperalgesia” are tossed out as the “real reason” we hurt even though we take opioids.

No matter how the argument goes, we are blamed for our pain and vilified if we dare take opioid medication for it.

The implications of some of the above definitions may be summarized for convenience as follows:
Allodynia lowered threshold stimulus and response mode differ
Hyperalgesia increased response stimulus and response mode are the same
Hyperpathia raised threshold: increased response stimulus and response mode may be the same or different
Hypoalgesia raised threshold: lowered response stimulus and response mode are the same


1 thought on “Classification of Chronic Pain – IASP Pain Terminology

  1. Kathy C

    We have all been the victims of a Psy Ops, propaganda campaign. These terms are vague by design, in order to make it easier to create denial. The terns that facilitate billing or offer protection from accountability are the ones that will be used. It is very clear that “opioid induced hyperalgia” may not even exist, or it is a distortion of some biased research on mice. The refusal to provide clear distinct language to this topic, and to amplify terms like OID, is part of a much bigger attack on the nature of reality.

    “Where we have real unmet need, if we’re talking about management of acute pain, is in our non-opioid options. There is still no real evidence to date that opioids work any better than Advil and Tylenol—even for acute pain, even in the ER. But opioids are addictive, which makes the pursuit of new uses for them a lucrative one. You will not find Big Pharma nor the DOD sponsoring research of exciting new uses for Tylenol, though from a public-health perspective—rather than a financial one—they probably should be.” ”

    The false “controversy’ over the approval of Desuvia, is one frightening example of the ignorance and stupidity. Most of the articles refer back to the thoroughly discredited “Krebs Study” and the variations on “Opioids No Better Than Tylenol,” attention getting article that passed through the media a couple of years ago. They attempt to conflate the pain that occurs with certain elbow and knee arthritic conditions to battlefield injuries. The DOD has to consider the worst battlefield injuries and the possibility of things like radiations burns. The true horror of the injuries that are in inflicted on our service members, is never discussed in these articles. To even suggest that Tylenol could treat a person with burns over most of their body or their legs crushed or blown off, is horrific.

    We should be asking questions about taking a drug that has been used for a couple of decades, reformulating it, and marketing it under patent of sale to the DOD, and the funding behind it. In this ill informed article, which makes dangerous assertions about horrific battle field injuries, that they could be treated with Tylenol, or acetaminophen, downplays the danger risks and horrors of war. Of course there is no research, it would not be ethical to test a patients with horrific life ending injuries with no medication versus one with the medication.

    We need to be weeding through the lies and propaganda that are inflicted on all of us daily. Articles like this look as if they are questioning the pharmaceutical industry when in fact they are repeating lies and propaganda of the medical industry, and military industrial complex. Downplaying the effect of pain, even in horrifically wounded soldiers is the intent here. Perdues strategy to continue to market Oxycontin was to demonize the addicted, and undermine the regulatory apparatus, with the help of corporate media. The corporate media is still misreporting on this topic, and misinforming the public. The death rate appears to be going up, while corporate media continues the misinformation campaign.

    Liked by 1 person


Other thoughts?

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.