A New Definition for "Pain"

In his decision on a 1964 landmark obscenity case, Supreme Court Justice Potter Stewart famously said he couldn’t define pornography “but I know it when I see it.”

Anyone trying to define pain may have a similar response. We know when we suffer pain but trying to put into words what the actual sensation is beyond simply saying “if it hurts, it’s pain” is a major challenge.

A task force formed by The International Association for Study of Pain (IASP), the major international organization for medical professionals involved in the study and treatment of pain, recently released a revised definition of pain.

The revision replaces the definition first developed by the IASP Subcommittee on Taxonomy and adopted by the IASP in 1979. Pain was defined as:

“An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.”

Accompanying the definition was a note that read in part:

“Pain is always subjective. Each individual learns the application of the word through experiences related to injury in early life….Many people report pain in the absence of tissue damage or any likely patholophysiological cause; usually this happens for psychological reasons…Activity induced in the nociceptor and nociceptive pathways by a noxious stimulus is not pain, which is always a psychological state, even though we may well appreciate that pain most often has a proximate cause.”

This IASP definition has been widely accepted by many medical and governmental organizations including the World Health Organization.

Lingering question

What has always been a great curiosity to me is how many times medical professionals would choose to present just the definition and exclude any mention of the note. I’ve always felt that one of the reasons for the choice was that a majority of doctors in this country who have specialized in pain management are anesthesiologists and it might be a bit uncomfortable for them to try to explain why they should be the leaders in treating something which is “always a psychological state.”

Having served for several years on the IASP Subcommittee on Taxonomy, I know that ever since the above definition was presented, there have been many discussions on its accuracy and whether a revision was required. Although over the years, the IASP has made changes to a number of terms related to pain based on new research, there was little to suggest that another definition of pain itself would prove to be marked improvement.

Recent history

In 2018, an IASP task force was formed to specifically focus on the definition of pain and to recommend whether the definition and the accompanying note “should be retained or changed based on current evidence-based knowledge.” (p.1977)

The task force decided that the definition should meet several requirements. It should:

• Apply to both acute and chronic pain and to all forms of pain no matter what the pathophysiology;
• Apply to humans and animals;
• Be defined whenever possible from the perspective of the person experiencing the pain and not an external observer.

Signaling just how many factors are considered to be involved in pain, the task force sought input from not only healthcare professionals but also ethicists and philosophers.

The task force noted that it received several key comments on its proposals including that the definition

• should be simple and practical
• its reference to tissue injury should be better aligned with modern conceptualizations of pain
• should better capture the personal experience of pain
• should provide more specificity regarding the various components of pain

The task force initially recommended that the definition be changed to:

“An aversive sensory and emotional experience typically caused by, or resembling that caused by, actual or potential tissue injury.”

However, there were concerns about use of the word “aversive” regarding the clarity of its meaning and the difficulty of its translation into many languages. It was also noted that in certain situations while pain may be unpleasant it may not be avoided such as with athletes. The task force decided to retain the word “unpleasant” from the previous definition.

There were also concerns about the indication of emphasis on tissue injury by the words “resembling that caused by” and it was decided to retain the words “association with.”

The final definition decided upon is:

“An unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential damage.”

The changes from the previous definition were to add the words “or resembling that associated with” and to eliminate the words “described in terms of such damage.”

The latter change was made to deemphasize tissue damage as the cause of pain; in many types of pain and especially of chronic pain, there is often no clear correlation between the presence or severity of tissue damage and the presence or severity of pain.

There are more significant changes in the notes accompanying the definition and clarifying how we should view pain. The new notes were put into bullet form:

The new notes complete the picture

There were several goals for the revision of the notes the most important of which is the recognition that pain is an individual experience and that because of its multifactorial nature we must understand that when it comes to pain, everyone is different.

I believe this is very important point as healthcare professionals often determine what level of pain they may expect a patient to experience and treat it based on that reported by other patients with the same physical health problems. Unfortunately, this often results as the pain being dismissed or undertreated if the patient reports a greater level than others.

Also important is inclusion of the statement that we need to recognize that the inability of a person to verbally express that he or she is experiencing pain does not mean an absence of pain. Although this certainly applies to animals, it also applies to many humans, most notably those who cannot verbally convey their pain, eg, cognitively impaired geriatric patients and pediatric patients too young to be able to describe their pain.

Repeated studies have demonstrated that these two groups are among those whose pain is most poorly managed by healthcare professionals.

As to the difference between pain and nociception, the task force noted that the latter refers to “activity that occurs in the nervous system in response to a noxious stimulus.”

Although little change was made in the definition itself, revisions to the accompanying notes do help clarify our current understanding of pain and they are now presented in more accessible format. In running prose, the notes were often ignored when the definition of pain was discussed. The simple bulleted list will no doubt make them both more understandable and more useful.

And for those interested in words, the notes also include a brief discussion of the etymology of the word “pain.”

No doubt this is not the final version of either the definition or the notes as our knowledge of what pain is continues to evolve as new research highlights both what we now know about it and, perhaps of even greater importance, the many mysteries about it that remain to be solved.

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Reference: Raja SN, Carr DB, Cohen C, et al. The revised International Association for the Study of Pain definition of pain: concepts, challenges, and compromises.​ Pain. 2020;161:1976-1982.