“Only that which never ceases to hurt stays in the memory,” philosopher Friedrich Nietzsche said about pain. For him, pain is central to human existence, and its function is to make us remember. For as long as humans have been around, we have been constructing theories about pain. What brings it about, why it exists, and how to measure it. In a sense, Nietzsche was quite right; pain does make us remember. And unbeknownst to him in the 1800s, the mnemonic function of pain provides an evolutionary benefit. Pain tells the body what is harmful and what must be avoided if we want to survive.
Expressing Pain
Despite its evolutionary benefit, pain has always been a profound source of human distress. Perhaps its most troubling feature is its inexpressibility, which creates a dilemma for patients and physicians alike. In “The Body in Pain,” Elaine Scarry, PhD, Cabot Professor of Aesthetics at Harvard University and a Senior Fellow at Harvard’s Society of Fellows, observes that pain resists language.1 At its extremes, it can leave the person experiencing it literally unable to speak. Even mild pain, however, can be difficult to describe. Fear and happiness usually have an object: You are afraid of something or happy about something. Physical pain is different. It has no object. You are not in pain of something; you are simply in pain.
Sufferers of chronic pain often comment on the deeply isolating aspect of their pain—a direct consequence of its inexpressibility and subjectivity. In her memoir about illness, author Elisabeth Tova Bailey writes of the “unbridgeable divide” that widens between someone who is in pain and their loved ones.2 This inexpressibility of pain makes it the ultimate challenge and test for our empathy. None of us are strangers to hearing a friend or family member complain about some pain they have and then secretly wondering in the back of our minds if it’s really that bad.
Theorists of the mind may be quick to point out that no one can know what someone else’s experiences are like in all cases, not just pain. This is the concept of qualia, of subjective experience. How do I know that I experience the color red in the same way you do? I don’t know, of course. And while qualia apply to a great number of situations, pain is the one that matters the most. It usually doesn’t matter if the red I see is the red you see, or if the smell of a jasmine flower is the same for me as it is for you, but it matters deeply if you truly believe I am experiencing the pain I say I am.
This has great implications for patients and their physicians. Patients, above all, need to feel heard and believed to feel cared for. And physicians need to understand how the patient feels, as accurately as possible, to provide the best possible care.
This has made understanding pain and finding ways to communicate it a prominent endeavor in the history of medicine, going back to antiquity. Early theories of pain were focused on explaining what it was and where it came from. Some of the oldest texts we have about pain are from 3500 B.C.E. in Mesopotamia, where it was understood that pain and illnesses had a supernatural cause, such as demons and omens sent by gods to interfere with the body. While we now understand much more about the physical causes and pathways of pain, its early mystical quality has not entirely left us. Pain—and suffering, more broadly—is still attributed to divine punishment or will in some religions.
Hippocrates of Kos, whose legacy is enshrined in the Hippocratic oath, believed that imbalances in the four humors of the body were what caused pain and that pain could be relieved by correcting these imbalances. Over a millennium later, Ibn Sina, also known as Avicenna, described pain as a sign of something that has occurred in the body, rather than a disease in itself, a concept we still largely adhere to in our understanding of pain as a symptom of an underlying problem.
In the 17th century, philosopher René Descartes described nerves as fine wires that connected the tissues to the brain, providing sensation. This, along with other work throughout the following two centuries, paved the way for physiologist Moritz Schiff to propose the specificity theory of pain that stated that pain follows a pathway separate from the other senses. This was contrasted by the pattern theory of neurologist Wilhelm Erb, which stated that any stimulus, when intense enough, could cause pain. Variations of both these theories are still being iterated and researched today.3
Measuring Pain
After Descartes, scientific and medical communities started to propose ways that pain could be formally measured and scaled.4 In the 19th century, psychophysicists delivered painful stimuli to tissue and attempted to quantify each participant’s pain threshold and tolerance or the magnitude and rating of the pain felt. An example of this type of assessment was the dolorimeter, a device created in 1940 by researchers James D. Hardy, Harold G. Wolff, and Helen Goodell at Cornell University that applied pressure, heat, or electric stimuli and measured participants’ responses. Using the results from the dolorimeter, they created the 10-level Hardy-Wolff-Goodell pain scale. However, other researchers were unable to reproduce these results, and their pain scale never reached widespread use.5
Henry K. Beecher, an anesthesiologist and medical ethicist, was one of the scientists who expressed doubt about the dolorimeter’s applicability and paved the way for more familiar pain assessments that use patients’ own subjective ratings. For example, the McGill Pain Questionnaire, developed in 1971, proposes three components of pain—sensory, evaluative, and affective—and provides patients with 78 words split into those categories (plus a “miscellaneous” category) that they can select to describe their pain.6
The most common currently used pain assessments are numeric rating scales, such as the NRS-11, an 11-point scale where 0 is no pain at all, and 10 is the worst pain imaginable. Other qualities of pain that may be assessed in different scales, such as the Brief Pain Inventory, include how much the pain interferes with a patient’s activities of daily living (ADLs).7 While assessments like these are incredibly useful and have had their utility validated in studies, they still do not capture the incredibly complex and individual experience of pain.8
For example, the “worst pain imaginable” depends on the patient’s imagination. Someone who has experienced severe injury or childbirth may be able to imagine a much greater pain than someone who has never suffered more physical pain than a stubbed toe. Or, when an assessment asks about how much the pain interferes with ADLs, someone who has experienced chronic pain for a long time may have learned to operate “normally” while bearing a high degree of pain, perhaps a level of pain that left them doubled over or bedridden when they first experienced it. It’s not clear that the pain has actually decreased in severity, despite it interfering with ADLs less, but this is a nuance that a numerical scale cannot capture.
Evidently, despite our thousands of years of theorizing and experimenting, continued research on pain assessment is needed. Recent studies are promising, demonstrating that there are alternatives to the commonly used NRS that may be just as easy to use for practitioners and preferred by patients.
A 2024 study conducted over 18 months in an adult inpatient setting found that the Functional Pain Scale (FPS), a three-question pain questionnaire, was preferred over the NRS by 77% of patients always or most of the time and judged by nurses as feasible to implement.9 A 2024 five-month study in patients recovering from orthopedic surgery evaluated the Interventional Pain Assessment (IPA), a one-question assessment, and found that 89.3% of patients and 76% of nurses preferred the IPA over the NRS.10
Given the limited settings in which the FPS and IPA have been studied so far and that these studies focused solely on nursing workflow, additional research is needed before widespread implementation can be recommended. What is important to note is that both the FPS and IPA ask about pain tolerability and allow patients to answer in words rather than numbers, indicating qualities that may be helpful to patients when formulating improved pain assessments and pursuing assessment standardization.
It seems to be an essential fact of the mind that others’ experiences, exactly as they experience them, will forever remain inaccessible to the self, regardless of how sophisticated a pain scale is. However, recent research shows that there is still great value in improving upon the NRS and other commonly used assessments by considering patient feedback and preferences. No matter how many cases of pain a clinician has seen, patients understand the lived experience of their own pain the best, and the best we can do is to learn from them as we seek to improve the care we provide for them.
Ms. Hsu
Jessie Hsu is a second-year medical student at the University of South Florida Morsani College of Medicine in Tampa, Fla.
References
- Scarry E. The Body in Pain: The Making and Unmaking of the World. New York: Oxford University Press; 1985.
- Bailey ET. The Sound of a Wild Snail Eating. Chapel Hill: Algonquin Books; 2010.
- Vincenot M, et al. A 5000-year overview of the history of pain through ancient civilizations to modern pain theories. Pain Rep. 2025;10(3):e1241. doi:10.1097/PR9.0000000000001241.
- Mogil JS. The history of pain measurement in humans and animals. Front Pain Res (Lausanne). 2022;3:1031058. doi:10.3389/fpain.2022.1031058.
- Tousignant N. The rise and fall of the dolorimeter: pain, analgesics, and the management of subjectivity in mid-twentieth-century United States. J Hist Med Allied Sci. 2011;66(2):145-79. doi:10.1093/jhmas/jrq024.
- Noble B, et al. The measurement of pain, 1945-2000. J Pain Symptom Manage. 2005;29(1):14-21. doi:10.1016/j.jpainsymman.2004.08.007.
- Walk D, Poliak-Tunis M. Chronic pain management: an overview of taxonomy, conditions commonly encountered, and assessment. Med Clin North Am. 2016;100(1):1-16. doi:10.1016/j.mcna.2015.09.005.
- Hjermstad MJ, et al. Studies comparing numerical rating scales, verbal rating scales, and visual analogue scales for assessment of pain intensity in adults: a systematic literature review. J Pain Symptom Manage. 2011;41(6):1073-93. doi:10.1016/j.jpainsymman.2010.08.016.
- Hanson A, et al. Implementing an evidence-based functional pain assessment scale in an adult inpatient unit. Pain Manag Nurs. 2024;25(4):330-337. doi:10.1016/j.pmn.2024.03.004.
- Boggs L, et al. Original research: improving pain assessment after inpatient orthopedic surgery: a comparison of two scales. Am J Nurs. 2024;124(12):18-25. doi:10.1097/01.NAJ.0001094532.56392.71.