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Pain is a distressing feeling often caused by intense or damaging
stimuli A stimulus is something that causes a physiological response. It may refer to: *Stimulation **Stimulus (physiology), something external that influences an activity **Stimulus (psychology), a concept in behaviorism and perception *Stimulus (economi ...
. The
International Association for the Study of Pain The International Association for the Study of Pain (IASP) is an international learned society promoting research, education, and policies for the understanding, prevention, and treatment of pain. IASP was founded in 1973 under the leadership of ...
defines pain as "an unpleasant sensory and
emotion Emotions are physical and mental states brought on by neurophysiology, neurophysiological changes, variously associated with thoughts, feelings, behavior, behavioral responses, and a degree of pleasure or suffering, displeasure. There is ...
al experience associated with, or resembling that associated with, actual or potential tissue damage." Pain motivates
organism An organism is any life, living thing that functions as an individual. Such a definition raises more problems than it solves, not least because the concept of an individual is also difficult. Many criteria, few of them widely accepted, have be ...
s to withdraw from damaging situations, to protect a damaged body part while it heals, and to avoid similar experiences in the future.
Congenital insensitivity to pain Congenital insensitivity to pain (CIP), also known as congenital analgesia, is an inability for a person to feel physical pain due to various rare genetic conditions. CIP is caused by genetic mutations that affect the development or function of no ...
may result in reduced
life expectancy Human life expectancy is a statistical measure of the estimate of the average remaining years of life at a given age. The most commonly used measure is ''life expectancy at birth'' (LEB, or in demographic notation ''e''0, where '' ...
. Most pain resolves once the
noxious stimulus A noxious stimulus is a stimulus strong enough to threaten the body's integrity (i.e. cause damage to tissue). Noxious stimulation induces peripheral afferents responsible for transducing pain (including A-delta and C- nerve fibers, as well a ...
is removed and the body has healed, but it may persist despite removal of the stimulus and apparent healing of the body. Sometimes pain arises in the absence of any detectable stimulus, damage or disease. Pain is the most common reason for physician consultation in most developed countries. It is a major symptom in many medical conditions, and can interfere with a person's
quality of life Quality of life (QOL) is defined by the World Health Organization as "an individual's perception of their position in life in the context of the culture and value systems in which they live and in relation to their goals, expectations, standards ...
and general functioning. People in pain experience impaired concentration,
working memory Working memory is a cognitive system with a limited capacity that can Memory, hold information temporarily. It is important for reasoning and the guidance of decision-making and behavior. Working memory is often used synonymously with short-term m ...
, mental flexibility, problem solving and information processing speed, and are more likely to experience irritability, depression, and anxiety. Simple pain medications are useful in 20% to 70% of cases. Psychological factors such as
social support Social support is the perception and actuality that one is cared for, has assistance available from other people, and, most popularly, that one is part of a supportive social network. These supportive resources can be emotional (e.g., nurturance), ...
,
cognitive behavioral therapy Cognitive behavioral therapy (CBT) is a form of psychotherapy that aims to reduce symptoms of various mental health conditions, primarily depression, PTSD, and anxiety disorders. Cognitive behavioral therapy focuses on challenging and chang ...
, excitement, or distraction can affect pain's intensity or unpleasantness.


Etymology

First attested in English in 1297, the word ''peyn'' comes from the
Old French Old French (, , ; ) was the language spoken in most of the northern half of France approximately between the late 8th -4; we might wonder whether there's a point at which it's appropriate to talk of the beginnings of French, that is, when it wa ...
''peine'', in turn from Latin ''poena'' meaning "punishment, penalty" (also meaning "torment, hardship, suffering" in Late Latin) and that from Greek language">Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...
ποινή (''poine''), generally meaning "price paid, penalty, punishment".


Classification

In many cases, pain fits into one or a combination of three categories: * Nociceptive pain (caused by inflamed or damaged tissue that activates pain sensors called nociceptors). Nociceptive pain is divided into "superficial" and "deep" pain. Deep pains are divided into two parts: "deep physical" and "deep visceral" pain. *
Neuropathic pain Neuropathic pain is pain caused by a lesion or disease of the somatosensory nervous system. Neuropathic pain may be associated with abnormal sensations called dysesthesia or pain from normally non-painful stimuli (allodynia). It may have continuo ...
(caused by damage or malfunction of the
nervous system In biology, the nervous system is the complex system, highly complex part of an animal that coordinates its behavior, actions and sense, sensory information by transmitting action potential, signals to and from different parts of its body. Th ...
). Neuropathic pain is divided into "
peripheral A peripheral device, or simply peripheral, is an auxiliary hardware device that a computer uses to transfer information externally. A peripheral is a hardware component that is accessible to and controlled by a computer but is not a core compo ...
" (the source being the
peripheral nervous system The peripheral nervous system (PNS) is one of two components that make up the nervous system of Bilateria, bilateral animals, with the other part being the central nervous system (CNS). The PNS consists of nerves and ganglia, which lie outside t ...
) and " central" (being from brain and spinal cord).
Peripheral neuropathy Peripheral neuropathy, often shortened to neuropathy, refers to damage or disease affecting the nerves. Damage to nerves may impair sensation, movement, gland function, and/or organ function depending on which nerve fibers are affected. Neuropa ...
is often described as "burning", "tingling", "electrical", "stabbing", or "pins and needles". *
Nociplastic pain Nociplastic pain, formerly known as central sensitisation, is chronic pain that persists without evidence of tissue injury, resulting in and being sustained by aberrant or heightened pain signal processing of the central nervous system (CNS). I ...
is pain that arises despite no clear evidence of tissue or somatosensory system damage causing the pain. In 1994, the
International Association for the Study of Pain The International Association for the Study of Pain (IASP) is an international learned society promoting research, education, and policies for the understanding, prevention, and treatment of pain. IASP was founded in 1973 under the leadership of ...
recommended using specific features to describe a patient's pain: # Region of the body involved (e.g., abdomen or lower limbs) # System whose dysfunction may be causing the pain (e.g., nervous or gastrointestinal systems) # Duration and pattern of occurrence # Intensity # Cause


Chronic versus acute

Pain is usually transitory, lasting only until the noxious stimulus is removed or the underlying damage or pathology has healed. But some painful conditions, such as
rheumatoid arthritis Rheumatoid arthritis (RA) is a long-term autoimmune disorder that primarily affects synovial joint, joints. It typically results in warm, swollen, and painful joints. Pain and stiffness often worsen following rest. Most commonly, the wrist and h ...
,
peripheral neuropathy Peripheral neuropathy, often shortened to neuropathy, refers to damage or disease affecting the nerves. Damage to nerves may impair sensation, movement, gland function, and/or organ function depending on which nerve fibers are affected. Neuropa ...
,
cancer Cancer is a group of diseases involving Cell growth#Disorders, abnormal cell growth with the potential to Invasion (cancer), invade or Metastasis, spread to other parts of the body. These contrast with benign tumors, which do not spread. Po ...
, and
idiopathic An idiopathic disease is any disease with an unknown cause or mechanism of apparent spontaneous origin. For some medical conditions, one or more causes are somewhat understood, but in a certain percentage of people with the condition, the cause ...
pain, may persist for years. Pain that lasts a long time is called " chronic" or "persistent", and pain that resolves quickly is called " acute". Traditionally, the distinction between acute and chronic pain has relied upon an arbitrary interval of time between onset and resolution; the two most commonly used markers being 3 months and 6 months since the onset of pain, though some theorists and researchers have placed the transition from acute to chronic pain at 12 months. Others apply "acute" to pain that lasts less than 30 days, "chronic" to pain of at least six months' duration, and "subacute" to pain that lasts from one to six months. A popular alternative definition of "chronic pain", involving no arbitrarily fixed duration, is "pain that extends beyond the expected period of healing". Chronic pain may be classified as " cancer-related" or "benign."


Allodynia

Allodynia Allodynia is a condition in which pain is caused by a stimulus that does not normally elicit pain. For example, sunburn can cause temporary allodynia, so that usually painless stimuli, such as wearing clothing or running cold or warm water over ...
is pain experienced in response to an ordinarily painless stimulus. It has no biological function and is classified by characteristics of the stimuli as cold, heat, touch, pressure or a pinprick.


Phantom

Phantom pain Phantom pain is a Pain, painful perception that an individual experiences relating to a Limb (anatomy), limb or an Organ (biology), organ that is not physically part of the body, either because it was amputation, removed or was never there in the ...
is pain felt in a part of the body that has been
amputated Amputation is the removal of a limb or other body part by trauma, medical illness, or surgery. As a surgical measure, it is used to control pain or a disease process in the affected limb, such as malignancy or gangrene. In some cases, it is ...
or from which the brain no longer receives signals. It is a type of neuropathic pain. The
prevalence In epidemiology, prevalence is the proportion of a particular population found to be affected by a medical condition (typically a disease or a risk factor such as smoking or seatbelt use) at a specific time. It is derived by comparing the number o ...
of phantom pain in upper limb amputees is nearly 82%, and in lower limb amputees is 54%. One study found that eight days after amputation, 72% of patients had phantom limb pain, and six months later, 67% reported it. Some amputees experience continuous pain that varies in intensity or quality; others experience several bouts of pain per day, or it may reoccur less often. It is often described as shooting, crushing, burning, or cramping. If the pain is continuous for an extended period, parts of the intact body may become sensitized, so touching them evokes pain in the phantom limb. Phantom limb pain may accompany
urination Urination is the release of urine from the bladder through the urethra in Placentalia, placental mammals, or through the cloaca in other vertebrates. It is the urinary system's form of excretion. It is also known medically as micturition, v ...
or
defecation Defecation (or defaecation) follows digestion and is the necessary biological process by which organisms eliminate a solid, semisolid, or liquid metabolic waste, waste material known as feces (or faeces) from the digestive tract via the anus o ...
.
Local anesthetic A local anesthetic (LA) is a medication that causes absence of all sensation (including pain) in a specific body part without loss of consciousness, providing local anesthesia, as opposed to a general anesthetic, which eliminates all sensati ...
injections into the nerves or sensitive areas of the stump may relieve pain for days, weeks, or sometimes permanently, despite the drug wearing off in a matter of hours, and small injections of
hypertonic In chemical biology, tonicity is a measure of the effective osmotic pressure gradient; the water potential of two solutions separated by a partially-permeable cell membrane. Tonicity depends on the relative concentration of selective membran ...
saline into the soft tissue between vertebrae produces local pain that radiates into the phantom limb for ten minutes or so and may be followed by hours, weeks, or even longer of partial or total relief from phantom pain. Vigorous vibration or electrical stimulation of the stump, or current from electrodes surgically implanted onto the spinal cord, all produce relief in some patients.
Mirror box Mirror therapy (MT) or mirror visual feedback (MVF) is a therapy for pain or disability that affects one side of the patient more than the other side. It was invented by Vilayanur S. Ramachandran to treat post-amputation patients who had phantom ...
therapy produces the illusion of movement and touch in a phantom limb, which in turn may cause a reduction in pain.
Paraplegia Paraplegia, or paraparesis, is an impairment in motor or sensory function of the lower extremities. The word comes from Ionic Greek () "half-stricken". It is usually caused by spinal cord injury or a congenital condition that affects the neura ...
, the loss of sensation and voluntary motor control after serious spinal cord damage, may be accompanied by girdle pain at the level of the spinal cord damage,
visceral pain Visceral pain is defined as pain that results from the activation of nociceptors of the thoracic, pelvic, or abdominal viscera (organs) in the human body. Visceral structures are highly sensitive to distension (stretch), ischemia and inflammation, ...
evoked by a filling bladder or bowel, or, in five to ten percent of people with paraplegia, phantom body pain in areas of complete sensory loss. This phantom body pain is initially described as burning or tingling but may evolve into severe crushing or pinching pain or the sensation of fire running down the legs or of a knife twisting in the flesh. Onset may or may not occur immediately years after the disabling injury. Surgical treatment rarely provides lasting relief.


Breakthrough

Breakthrough pain is transitory pain that comes on suddenly and is not alleviated by the patient's regular
pain management Pain management is an aspect of medicine and health care involving relief of pain (pain relief, analgesia, pain control) in various dimensions, from acute (medicine), acute and simple to chronic condition, chronic and challenging. Most physici ...
. It is common in cancer patients who often have background pain that is generally well-controlled by medications but who also sometimes experience bouts of severe pain that, from time to time, "breaks through" the medication. The characteristics of breakthrough
cancer pain Pain in cancer may arise from a tumor compressing or infiltrating nearby body parts; from treatments and diagnostic procedures; or from skin, nerve and other changes caused by a hormone imbalance or immune response. Most chronic (long-lasting) pai ...
vary from person to person and according to the cause. Management of breakthrough pain can entail intensive use of
opioid Opioids are a class of Drug, drugs that derive from, or mimic, natural substances found in the Papaver somniferum, opium poppy plant. Opioids work on opioid receptors in the brain and other organs to produce a variety of morphine-like effects, ...
s, including
fentanyl Fentanyl is a highly potent synthetic piperidine opioid primarily used as an analgesic (pain medication). It is 30 to 50 times more Potency (pharmacology), potent than heroin and 50 to 100 times more potent than morphine. Its primary Medici ...
.


Asymbolia and insensitivity

The ability to experience pain is essential for protection from injury and recognition of the presence of injury. Episodic
analgesia Pain management is an aspect of medicine and health care involving relief of pain (pain relief, analgesia, pain control) in various dimensions, from acute and simple to chronic and challenging. Most physicians and other health professionals ...
may occur under special circumstances, such as in the excitement of sport or war: a soldier on the battlefield may feel no pain for many hours from a traumatic amputation or other severe injury. Although unpleasantness is an essential part of the IASP definition of pain,Alt URL
Derived from it is possible in some patients to induce a state known as pain asymbolia, described as intense pain devoid of unpleasantness, with
morphine Morphine, formerly also called morphia, is an opiate that is found naturally in opium, a dark brown resin produced by drying the latex of opium poppies (''Papaver somniferum''). It is mainly used as an analgesic (pain medication). There are ...
injection or
psychosurgery Psychosurgery, also called neurosurgery for mental disorder (NMD), is the neurosurgical treatment of mental disorders. Psychosurgery has always been a controversial medical field. The modern history of psychosurgery begins in the 1880s under ...
. Such patients report pain but are not bothered by it; they recognize the sensation of pain but suffer little or not at all. Indifference to pain can also rarely be present from birth; these people have normal nerves on medical investigations, and find pain unpleasant, but do not avoid repetition of the pain stimulus. Insensitivity to pain may also result from abnormalities in the
nervous system In biology, the nervous system is the complex system, highly complex part of an animal that coordinates its behavior, actions and sense, sensory information by transmitting action potential, signals to and from different parts of its body. Th ...
. This is usually the result of acquired damage to the nerves, such as
spinal cord injury A spinal cord injury (SCI) is damage to the spinal cord that causes temporary or permanent changes in its function. It is a destructive neurological and pathological state that causes major motor, sensory and autonomic dysfunctions. Symptoms of ...
,
diabetes mellitus Diabetes mellitus, commonly known as diabetes, is a group of common endocrine diseases characterized by sustained hyperglycemia, high blood sugar levels. Diabetes is due to either the pancreas not producing enough of the hormone insulin, or th ...
(
diabetic neuropathy Diabetic neuropathy includes various types of nerve damage associated with diabetes mellitus. The most common form, diabetic peripheral neuropathy, affects 30% of all diabetic patients. Studies suggests that cutaneous nerve branches, such as the s ...
), or
leprosy Leprosy, also known as Hansen's disease (HD), is a Chronic condition, long-term infection by the bacteria ''Mycobacterium leprae'' or ''Mycobacterium lepromatosis''. Infection can lead to damage of the Peripheral nervous system, nerves, respir ...
in countries where that disease is prevalent. These individuals are at risk of tissue damage and infection due to undiscovered injuries. People with diabetes-related nerve damage, for instance, sustain poorly healing foot ulcers as a result of decreased sensation. A much smaller number of people are insensitive to pain due to an inborn abnormality of the nervous system, known as "
congenital insensitivity to pain Congenital insensitivity to pain (CIP), also known as congenital analgesia, is an inability for a person to feel physical pain due to various rare genetic conditions. CIP is caused by genetic mutations that affect the development or function of no ...
". Children with this condition incur carelessly-repeated damage to their tongues, eyes, joints, skin, and muscles. Some die before adulthood, and others have a reduced life expectancy. Most people with congenital insensitivity to pain have one of five hereditary sensory and autonomic neuropathies (which includes
familial dysautonomia Familial dysautonomia (FD), also known as Riley–Day syndrome, is a rare, progressive, recessive genetic disorder of the autonomic nervous system that affects the development and survival of sensory, sympathetic, and some parasympathetic neuro ...
and congenital insensitivity to pain with anhidrosis). These conditions feature decreased sensitivity to pain together with other neurological abnormalities, particularly of the
autonomic nervous system The autonomic nervous system (ANS), sometimes called the visceral nervous system and formerly the vegetative nervous system, is a division of the nervous system that operates viscera, internal organs, smooth muscle and glands. The autonomic nervo ...
. A very rare syndrome with isolated congenital insensitivity to pain has been linked with mutations in the ''
SCN9A Sodium voltage-gated channel alpha subunit 9 (also Nav1.7) is a sodium ion channel that, in humans, is encoded by the ''SCN9A'' gene. It is usually expressed at high levels in two types of neurons: the nociceptive (pain) neurons at the dorsal ...
'' gene, which codes for a sodium channel ( Nav1.7) necessary in conducting pain nerve stimuli.


Functional effects

Experimental subjects challenged by acute pain and patients in chronic pain experience impairments in attention control, working memory capacity, mental flexibility, problem solving, and information processing speed. Pain is also associated with increased depression, anxiety, fear, and anger.


On subsequent negative emotion

Although pain is considered to be aversive and unpleasant and is therefore usually avoided, a
meta-analysis Meta-analysis is a method of synthesis of quantitative data from multiple independent studies addressing a common research question. An important part of this method involves computing a combined effect size across all of the studies. As such, th ...
which summarized and evaluated numerous studies from various psychological disciplines, found a reduction in
negative affect In psychology, negative affectivity (NA), or negative affect, is a personality variable that involves the experience of negative emotions and poor self-concept. Negative affectivity subsumes a variety of negative emotions, including anger, contem ...
. Across studies, participants that were subjected to acute physical pain in the laboratory subsequently reported feeling better than those in non-painful control conditions, a finding which was also reflected in physiological parameters. A potential mechanism to explain this effect is provided by the
opponent-process theory Opponent-process theory is a psychological and neurology, neurological model that accounts for a wide range of behaviors, including color vision. This model was first proposed in 1878 by Ewald Hering, a German physiologist, and later expanded by R ...
.


Theory


Historical

Before the relatively recent discovery of
neuron A neuron (American English), neurone (British English), or nerve cell, is an membrane potential#Cell excitability, excitable cell (biology), cell that fires electric signals called action potentials across a neural network (biology), neural net ...
s and their role in pain, various body functions were proposed to account for pain. There were several competing early theories of pain among the ancient Greeks:
Hippocrates Hippocrates of Kos (; ; ), also known as Hippocrates II, was a Greek physician and philosopher of the Classical Greece, classical period who is considered one of the most outstanding figures in the history of medicine. He is traditionally referr ...
believed that it was due to an imbalance in vital fluids.Linton. Models of Pain Perception. Elsevier Health, 2005. Print. In the 11th century,
Avicenna Ibn Sina ( – 22 June 1037), commonly known in the West as Avicenna ( ), was a preeminent philosopher and physician of the Muslim world, flourishing during the Islamic Golden Age, serving in the courts of various Iranian peoples, Iranian ...
theorized that there were a number of feeling senses, including touch, pain, and titillation. In 1644,
René Descartes René Descartes ( , ; ; 31 March 1596 – 11 February 1650) was a French philosopher, scientist, and mathematician, widely considered a seminal figure in the emergence of modern philosophy and Modern science, science. Mathematics was paramou ...
theorized that pain was a disturbance that passed along nerve fibers until the disturbance reached the brain. The work of Descartes and Avicenna prefigured the 19th-century development of ''specificity theory''. Specificity theory saw pain as "a specific sensation, with its own sensory apparatus independent of touch and other senses". Another theory that came to prominence in the 18th and 19th centuries was ''intensive theory'', which conceived of pain not as a unique sensory modality, but an emotional state produced by stronger than normal stimuli such as intense light, pressure or temperature. By the mid-1890s, ''specificity'' was backed primarily by physiologists and physicians, and psychologists mostly backed the ''intensive theory''. However, after a series of clinical observations by
Henry Head Sir Henry Head, FRS (4 August 1861 – 8 October 1940) was an English neurologist who conducted pioneering work into the somatosensory system and sensory nerves. Much of this work was conducted on himself, in collaboration with the psychiatri ...
and experiments by Max von Frey, the psychologists migrated to ''specificity'' almost en masse. By the century's end, most physiology and psychology textbooks presented pain ''specificity'' as fact.


Modern

Some sensory fibers do not differentiate between noxious and non-noxious stimuli, while others (i.e.,
nociceptor A nociceptor (; ) is a sensory neuron that responds to damaging or potentially damaging stimuli by sending "possible threat" signals to the spinal cord and the brain. The brain creates the sensation of pain to direct attention to the body part, ...
s) respond only to noxious, high-intensity stimuli. At the peripheral end of the nociceptor, noxious stimuli generate currents that, above a given threshold, send
signals A signal is both the process and the result of Signal transmission, transmission of data over some transmission media, media accomplished by embedding some variation. Signals are important in multiple subject fields including signal processin ...
along the nerve fiber to the spinal cord. The "specificity" (whether it responds to thermal, chemical, or mechanical features of its environment) of a nociceptor is determined by which
ion channel Ion channels are pore-forming membrane proteins that allow ions to pass through the channel pore. Their functions include establishing a resting membrane potential, shaping action potentials and other electrical signals by Gating (electrophysiol ...
s it expresses at its peripheral end. So far, dozens of types of nociceptor ion channels have been identified, and their exact functions are still being determined. The pain signal travels from the periphery to the spinal cord along A-delta and C fibers. Because the A-delta fiber is thicker than the C fiber, and is thinly sheathed in an electrically insulating material (
myelin Myelin Sheath ( ) is a lipid-rich material that in most vertebrates surrounds the axons of neurons to insulate them and increase the rate at which electrical impulses (called action potentials) pass along the axon. The myelinated axon can be lik ...
), it carries its signal faster (5–30  m/s) than the unmyelinated C fiber (0.5–2 m/s). Pain evoked by the A-delta fibers is described as sharp and is felt first. This is followed by a duller pain—often described as burning—carried by the C fibers. These A-delta and C fibers enter the spinal cord via
Lissauer's tract The posterolateral tract (fasciculus of Lissauer, Lissauer's tract, tract of Lissauer, dorsolateral fasciculus, dorsolateral tract, zone of Lissauer) is a small strand situated in relation to the tip of the posterior column close to the entrance of ...
and connect with spinal cord nerve fibers in the
central gelatinous substance of the spinal cord The central canal (also known as spinal foramen or ependymal canal) is the cerebrospinal fluid-filled space that runs through the spinal cord. The central canal lies below and is connected to the ventricular system of the brain, from which it r ...
. These spinal cord fibers then cross the cord via the
anterior white commissure The anterior white commissure (ventral white commissure) is a bundle of nerve fibers which cross the midline of the spinal cord just anterior (in front of) to the gray commissure ( Rexed lamina X). A delta fibers (Aδ fibers) and C fibers carr ...
and ascend in the
spinothalamic tract The spinothalamic tract is a nerve tract in the anterolateral system in the spinal cord. This tract is an ascending sensory pathway to the thalamus. From the ventral posterolateral nucleus in the thalamus, sensory information is relayed upwar ...
. Before reaching the brain, the spinothalamic tract splits into the
lateral Lateral is a geometric term of location which may also refer to: Biology and healthcare * Lateral (anatomy), a term of location meaning "towards the side" * Lateral cricoarytenoid muscle, an intrinsic muscle of the larynx * Lateral release ( ...
, neospinothalamic tract and the
medial Medial may refer to: Mathematics * Medial magma, a mathematical identity in algebra Geometry * Medial axis, in geometry the set of all points having more than one closest point on an object's boundary * Medial graph, another graph that repr ...
, paleospinothalamic tract. The neospinothalamic tract carries the fast, sharp A-delta signal to the ventral posterolateral nucleus of the
thalamus The thalamus (: thalami; from Greek language, Greek Wikt:θάλαμος, θάλαμος, "chamber") is a large mass of gray matter on the lateral wall of the third ventricle forming the wikt:dorsal, dorsal part of the diencephalon (a division of ...
. The paleospinothalamic tract carries the slow, dull C fiber pain signal. Some of the paleospinothalamic fibers peel off in the brain stem—connecting with the reticular formation or midbrain periaqueductal gray—and the remainder terminate in the intralaminar nuclei of the thalamus. Pain-related activity in the thalamus spreads to the
insular cortex The insular cortex (also insula and insular lobe) is a portion of the cerebral cortex folded deep within the lateral sulcus (the fissure separating the temporal lobe from the parietal lobe, parietal and frontal lobes) within each brain hemisphere ...
(thought to embody, among other things, the feeling that distinguishes pain from other
homeostatic emotion Homeostatic feeling is a class of feelings (e.g. thirst, fatigue, pain, desire, malaise, well-being) that inform us about our physiological condition. In his earlier work Antonio Damasio used "primordial feeling" but he now prefers the term "homeos ...
s such as itch and nausea) and
anterior cingulate cortex In human brains, the anterior cingulate cortex (ACC) is the frontal part of the cingulate cortex that resembles a "collar" surrounding the frontal part of the corpus callosum. It consists of Brodmann areas 24, 32, and 33. It is involved ...
(thought to embody, among other things, the affective/motivational element, the unpleasantness of pain), and pain that is distinctly located also activates the
primary Primary or primaries may refer to: Arts, entertainment, and media Music Groups and labels * Primary (band), from Australia * Primary (musician), hip hop musician and record producer from South Korea * Primary Music, Israeli record label Work ...
and
secondary somatosensory cortex The human secondary somatosensory cortex (S2, SII) is a region of sensory cortex in the parietal operculum on the ceiling of the lateral sulcus. Region S2 was first described by Adrian in 1940, who found that feeling in cats' feet was not only r ...
. Spinal cord fibers dedicated to carrying A-delta fiber pain signals and others that carry both A-delta and C fiber pain signals to the
thalamus The thalamus (: thalami; from Greek language, Greek Wikt:θάλαμος, θάλαμος, "chamber") is a large mass of gray matter on the lateral wall of the third ventricle forming the wikt:dorsal, dorsal part of the diencephalon (a division of ...
have been identified. Other spinal cord fibers, known as
wide dynamic range neuron The wide dynamic range (WDR) neuron was first discovered by Mendell in 1966. Early studies of this neuron established what is known as the Gate control theory, gate control theory of pain. The basic concept is that non-painful stimuli block the path ...
s, respond to A-delta and C fibers and the much larger, more heavily myelinated A-beta fibers that carry touch, pressure, and vibration signals.
Ronald Melzack Ronald Melzack (July 19, 1929 – December 22, 2019) was a Canadian psychologist and professor of psychology at McGill University. In 1965, he and Patrick David Wall re-charged pain research by introducing the gate control theory of pain. In 19 ...
and Patrick Wall introduced their
gate control theory The gate control theory of pain asserts that non-painful input closes the nerve "gates" to painful input, which prevents pain sensation from traveling to the central nervous system. The gate control theory of pain describes how non-painful sensati ...
in the 1965 ''Science'' article "Pain Mechanisms: A New Theory". The authors proposed that the thin C and A-delta (pain) and large diameter A-beta (touch, pressure, vibration) nerve fibers carry information from the site of injury to two destinations in the dorsal horn of the spinal cord, and that A-beta fiber signals acting on inhibitory cells in the dorsal horn can reduce the intensity of pain signals sent to the brain.


Three dimensions of pain

In 1968,
Ronald Melzack Ronald Melzack (July 19, 1929 – December 22, 2019) was a Canadian psychologist and professor of psychology at McGill University. In 1965, he and Patrick David Wall re-charged pain research by introducing the gate control theory of pain. In 19 ...
and Kenneth Casey described chronic pain in terms of its three dimensions: * "sensory-discriminative" (sense of the intensity, location, quality, and duration of the pain), * "affective-motivational" (unpleasantness and urge to escape the unpleasantness) and * "cognitive-evaluative" (cognitions such as appraisal, cultural values, distraction, and hypnotic suggestion). They theorized that pain intensity (the sensory discriminative dimension) and unpleasantness (the affective-motivational dimension) are not simply determined by the magnitude of the painful stimulus, but "higher" cognitive activities can influence perceived intensity and unpleasantness. Cognitive activities may affect both sensory and affective experience, or they may modify primarily the affective-motivational dimension. Thus, excitement in games or war appears to block both the sensory-discriminative and affective-motivational dimensions of pain, while suggestion and placebos may modulate only the affective-motivational dimension and leave the sensory-discriminative dimension relatively undisturbed. (p. 432) The paper ends with a call to action: "Pain can be treated not only by trying to cut down the sensory input by anesthetic block, surgical intervention and the like, but also by influencing the motivational-affective and cognitive factors as well." (p. 435)


Evolutionary and behavioral role

Pain is part of the body's defense system, producing a reflexive retraction from the painful stimulus, and tendencies to protect the affected body part while it heals, and avoid that harmful situation in the future. It is an important part of animal life, vital to healthy survival. People with
congenital insensitivity to pain Congenital insensitivity to pain (CIP), also known as congenital analgesia, is an inability for a person to feel physical pain due to various rare genetic conditions. CIP is caused by genetic mutations that affect the development or function of no ...
have reduced
life expectancy Human life expectancy is a statistical measure of the estimate of the average remaining years of life at a given age. The most commonly used measure is ''life expectancy at birth'' (LEB, or in demographic notation ''e''0, where '' ...
. In '' The Greatest Show on Earth: The Evidence for Evolution'', biologist
Richard Dawkins Richard Dawkins (born 26 March 1941) is a British evolutionary biology, evolutionary biologist, zoologist, science communicator and author. He is an Oxford fellow, emeritus fellow of New College, Oxford, and was Simonyi Professor for the Publ ...
addresses the question of why pain should have the quality of being painful. He describes the alternative as a mental raising of a "red flag". To argue why that red flag might be insufficient, Dawkins argues that drives must compete with one another within living beings. The most "fit" creature would be the one whose pains are well balanced. Those pains which mean certain death when ignored will become the most powerfully felt. The relative intensities of pain, then, may resemble the relative importance of that risk to our ancestors. This resemblance will not be perfect, however, because natural selection can be a poor designer. This may have maladaptive results such as
supernormal stimuli A supernormal stimulus or superstimulus is an exaggerated version of a stimulation, stimulus to which there is an existing response tendency, or any stimulus that elicits a response more strongly than the stimulus for which it evolved. For exam ...
. Pain, however, does not only wave a "red flag" within living beings but may also act as a warning sign and a call for help to other living beings. Especially in humans who readily helped each other in case of sickness or injury throughout their evolutionary history, pain might be shaped by natural selection to be a credible and convincing signal of the need for relief, help, and care. Idiopathic pain (pain that persists after the trauma or pathology has healed, or that arises without any apparent cause) may be an exception to the idea that pain is helpful to survival, although some
psychodynamic Psychodynamics, also known as psychodynamic psychology, in its broadest sense, is an approach to psychology that emphasizes systematic study of the psychological forces underlying human behavior, feelings, and emotions and how they might relate t ...
psychologists argue that such pain is psychogenic, enlisted as a protective distraction to keep dangerous emotions unconscious.


Thresholds

In pain science, thresholds are measured by gradually increasing the intensity of a stimulus in a procedure called
quantitative sensory testing Quantitative sensory testing (QST) is a panel of diagnostic tests used to assess somatosensory function, in the context of research and as a supplemental tool in the diagnosis of somatosensory disorders, including pain insensitivity, painless and ...
which involves such stimuli as
electric current An electric current is a flow of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is defined as the net rate of flow of electric charge through a surface. The moving particles are called charge c ...
, thermal (heat or cold), mechanical (pressure, touch, vibration),
ischemic Ischemia or ischaemia is a restriction in blood supply to any tissue, muscle group, or organ of the body, causing a shortage of oxygen that is needed for cellular metabolism (to keep tissue alive). Ischemia is generally caused by problems ...
, or chemical stimuli applied to the subject to evoke a response. The " pain perception threshold" is the point at which the subject begins to feel pain, and the "pain threshold intensity" is the stimulus intensity at which the stimulus begins to hurt. The "
pain tolerance Pain tolerance is the maximum level of pain that a person is able to tolerate. Pain tolerance is distinct from pain threshold (the point at which pain begins to be felt).


Assessment

A person's self-report is the most reliable measure of pain. Some health care professionals may underestimate pain severity. A definition of pain widely employed in nursing, emphasizing its subjective nature and the importance of believing patient reports, was introduced by Margo McCaffery in 1968: "Pain is whatever the experiencing person says it is, existing whenever he says it does". To assess intensity, the patient may be asked to locate their pain on a scale of 0 to 10, with 0 being no pain at all, and 10 the worst pain they have ever felt. Quality can be established by having the patient complete the
McGill Pain Questionnaire The McGill Pain Questionnaire, also known as McGill Pain Index, is a scale of rating pain developed at McGill University by Melzack and Torgerson in 1971. It is a self-report questionnaire that allows individuals to give their doctor a good descr ...
indicating which words best describe their pain.


Visual analogue scale

The visual analogue scale is a common, reproducible tool in the assessment of pain and pain relief. The scale is a continuous line anchored by verbal descriptors, one for each extreme of pain where a higher score indicates greater pain intensity. It is usually 10 cm in length with no intermediate descriptors as to avoid marking of scores around a preferred numeric value. When applied as a pain descriptor, these anchors are often 'no pain' and 'worst imaginable pain". Cut-offs for pain classification have been recommended as no pain (0–4mm), mild pain (5–44mm), moderate pain (45–74mm) and severe pain (75–100mm).


Multidimensional pain inventory

The Multidimensional Pain Inventory (MPI) is a questionnaire designed to assess the
psychosocial The psychosocial approach looks at individuals in the context of the combined influence that psychological factors and the surrounding social environment have on their physical and mental wellness and their ability to function. This approach is ...
state of a person with chronic pain. Combining the MPI characterization of the person with their IASP five-category pain profile is recommended for deriving the most useful case description.


Assessment in non-verbal people

Non-verbal Nonverbal communication is the transmission of messages or signals through a nonverbal platform such as eye contact (oculesics), body language (kinesics), social distance (proxemics), touch ( haptics), voice ( prosody and paralanguage), physical ...
people cannot use words to tell others that they are experiencing pain. However, they may be able to communicate through other means, such as blinking, pointing, or nodding. With a non-communicative person, observation becomes critical, and specific behaviors can be monitored as pain indicators. Behaviors such as facial grimacing and guarding (trying to protect part of the body from being bumped or touched) indicate pain, as well as an increase or decrease in vocalizations, changes in routine behavior patterns and mental status changes. Patients experiencing pain may exhibit withdrawn
social behavior Social behavior is behavior among two or more organisms within the same species, it encompasses any behavior in which one member affects another. Social behavior can be seen as similar to an exchange of goods, with the expectation that when you ...
and possibly experience a
decreased appetite Anorexia is a medical term for a loss of appetite. While the term outside of the scientific literature is often used interchangeably with anorexia nervosa, many possible causes exist for a loss of appetite, some of which may be harmless, while o ...
and decreased nutritional intake. A change in condition that deviates from baseline, such as moaning with movement or when manipulating a body part, and limited
range of motion Range of motion (or ROM) is the linear or angular distance that a moving object may normally travel while properly attached to another. In biomechanics and strength training, ROM refers to the angular distance and direction a joint can move be ...
are also potential pain indicators. In patients who possess language but are incapable of expressing themselves effectively, such as those with dementia, an increase in confusion or display of aggressive behaviors or agitation may signal that discomfort exists, and further assessment is necessary. Changes in behavior may be noticed by caregivers who are familiar with the person's normal behavior. Infants do feel pain, but lack the language needed to report it, and so communicate distress by crying. A non-verbal pain assessment should be conducted involving the parents, who will notice changes in the infant which may not be obvious to the health care provider. Pre-term babies are more sensitive to painful stimuli than those carried to full term. Another approach, when pain is suspected, is to give the person treatment for pain, and then watch to see whether the suspected indicators of pain subside.


Other reporting barriers

The way in which one experiences and responds to pain is related to sociocultural characteristics, such as gender, ethnicity, and age. An aging adult may not respond to pain in the same way that a younger person might. Their ability to recognize pain may be blunted by illness or the use of
medication Medication (also called medicament, medicine, pharmaceutical drug, medicinal product, medicinal drug or simply drug) is a drug used to medical diagnosis, diagnose, cure, treat, or preventive medicine, prevent disease. Drug therapy (pharmaco ...
. Depression may also keep older adult from reporting they are in pain. Decline in
self-care Self-care has been defined as the process of establishing behaviors to ensure holistic well-being of oneself, to promote health, and actively manage illness when it occurs. Individuals engage in some form of self-care daily with food choices, ...
may also indicate the older adult is experiencing pain. They may be reluctant to report pain because they do not want to be perceived as weak, or may feel it is impolite or shameful to complain, or they may feel the pain is a form of deserved punishment. Cultural barriers may also affect the likelihood of reporting pain. Patients may feel that certain treatments go against their religious beliefs. They may not report pain because they feel it is a sign that death is near. Many people fear the stigma of addiction, and avoid pain treatment so as not to be prescribed potentially addicting drugs. Many Asians do not want to lose respect in society by admitting they are in pain and need help, believing the pain should be borne in silence, while other cultures feel they should report pain immediately to receive immediate relief. Gender can also be a perceived factor in reporting pain.
Gender differences Sex differences in humans have been studied in a variety of fields. Sex determination generally occurs by the presence or absence of a Y chromosome in the 23rd pair of chromosomes in the human genome. ''Phenotypic sex'' refers to an individua ...
can be the result of social and cultural expectations, with, in some cultures, women expected to be more emotional and show pain, and men to be more stoic. As a result, female pain may be at a higher risk of being stigmatized, leading to less urgent treatment of women based on social expectations of their ability to accurately report it. This has been postulated to lead to extended emergency room wait times for women and frequent dismissal of their ability to accurately report pain.


Diagnostic aid

Pain is a symptom of many medical conditions. Knowing the time of onset, location, intensity, pattern of occurrence (continuous, intermittent, etc.), exacerbating and relieving factors, and quality (burning, sharp, etc.) of the pain will help the examining physician to accurately diagnose the problem. For example, chest pain described as extreme heaviness may indicate
myocardial infarction A myocardial infarction (MI), commonly known as a heart attack, occurs when Ischemia, blood flow decreases or stops in one of the coronary arteries of the heart, causing infarction (tissue death) to the heart muscle. The most common symptom ...
, while chest pain described as tearing may indicate
aortic dissection Aortic dissection (AD) occurs when an injury to the innermost layer of the aorta allows blood to flow between the layers of the aortic wall, forcing the layers apart. In most cases, this is associated with a sudden onset of agonizing ches ...
.


Physiological measurement

Functional magnetic resonance imaging Functional magnetic resonance imaging or functional MRI (fMRI) measures brain activity by detecting changes associated with blood flow. This technique relies on the fact that cerebral blood flow and neuronal activation are coupled. When an area o ...
brain scanning has been used to measure pain, and correlates well with self-reported pain.


Mechanisms


Nociceptive

Nociceptive pain is caused by stimulation of sensory nerve fibers that respond to stimuli approaching or exceeding harmful intensity (
nociceptor A nociceptor (; ) is a sensory neuron that responds to damaging or potentially damaging stimuli by sending "possible threat" signals to the spinal cord and the brain. The brain creates the sensation of pain to direct attention to the body part, ...
s), and may be classified according to the mode of noxious stimulation. The most common categories are "thermal" (e.g. heat or cold), "mechanical" (e.g. crushing, tearing, shearing, etc.) and "chemical" (e.g.
iodine Iodine is a chemical element; it has symbol I and atomic number 53. The heaviest of the stable halogens, it exists at standard conditions as a semi-lustrous, non-metallic solid that melts to form a deep violet liquid at , and boils to a vi ...
in a cut or chemicals released during
inflammation Inflammation (from ) is part of the biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. The five cardinal signs are heat, pain, redness, swelling, and loss of function (Latin ''calor'', '' ...
). Some nociceptors respond to more than one of these modalities and are consequently designated polymodal. Nociceptive pain may also be classed according to the site of origin and divided into "visceral", "deep somatic" and "superficial somatic" pain. Visceral structures (e.g., the heart, liver and intestines) are highly sensitive to stretch,
ischemia Ischemia or ischaemia is a restriction in blood supply to any tissue, muscle group, or organ of the body, causing a shortage of oxygen that is needed for cellular metabolism (to keep tissue alive). Ischemia is generally caused by problems ...
and
inflammation Inflammation (from ) is part of the biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. The five cardinal signs are heat, pain, redness, swelling, and loss of function (Latin ''calor'', '' ...
, but relatively insensitive to other stimuli that normally evoke pain in other structures, such as burning and cutting.
Visceral pain Visceral pain is defined as pain that results from the activation of nociceptors of the thoracic, pelvic, or abdominal viscera (organs) in the human body. Visceral structures are highly sensitive to distension (stretch), ischemia and inflammation, ...
is diffuse, difficult to locate and often referred to a distant, usually superficial, structure. It may be accompanied by nausea and vomiting and may be described as sickening, deep, squeezing, and dull. ''Deep somatic'' pain is initiated by stimulation of nociceptors in ligaments, tendons, bones, blood vessels,
fascia A fascia (; : fasciae or fascias; adjective fascial; ) is a generic term for macroscopic membranous bodily structures. Fasciae are classified as superficial, visceral or deep, and further designated according to their anatomical location. ...
e and muscles, and is dull, aching, poorly-localized pain. Examples include
sprain A sprain is a soft tissue injury of the ligaments within a joint, often caused by a sudden movement abruptly forcing the joint to exceed its functional range of motion. Ligaments are tough, inelastic fibers made of collagen that connect two or ...
s and broken bones. ''Superficial somatic'' pain is initiated by activation of nociceptors in the skin or other superficial tissue, and is sharp, well-defined and clearly located. Examples of injuries that produce superficial somatic pain include minor wounds and minor (first degree) burns.


Neuropathic

Neuropathic pain is caused by damage or disease affecting any part of the
nervous system In biology, the nervous system is the complex system, highly complex part of an animal that coordinates its behavior, actions and sense, sensory information by transmitting action potential, signals to and from different parts of its body. Th ...
involved in bodily feelings (the
somatosensory system The somatosensory system, or somatic sensory system is a subset of the sensory nervous system. The main functions of the somatosensory system are the perception of external stimuli, the perception of internal stimuli, and the regulation of bod ...
). Neuropathic pain may be divided into peripheral, central, or mixed (peripheral and central) neuropathic pain.
Peripheral A peripheral device, or simply peripheral, is an auxiliary hardware device that a computer uses to transfer information externally. A peripheral is a hardware component that is accessible to and controlled by a computer but is not a core compo ...
neuropathic pain is often described as "burning", "tingling", "electrical", "stabbing", or "pins and needles". Bumping the " funny bone" elicits acute peripheral neuropathic pain. Some manifestations of neuropathic pain include: traumatic neuropathy,
tic douloureux A tic is a sudden and repetitive motor movement or vocalization that is not rhythmic and involves discrete muscle groups. Tics are typically brief and may resemble a normal behavioral characteristic or gesture. Tics can be invisible to the obs ...
, painful
diabetic neuropathy Diabetic neuropathy includes various types of nerve damage associated with diabetes mellitus. The most common form, diabetic peripheral neuropathy, affects 30% of all diabetic patients. Studies suggests that cutaneous nerve branches, such as the s ...
, and
postherpetic neuralgia Postherpetic neuralgia (PHN) is neuropathic pain that occurs due to damage to a peripheral nerve caused by the reactivation of the varicella zoster virus ( herpes zoster, also known as shingles). PHN is defined as pain in a dermatomal distributi ...
.


Nociplastic

Nociplastic pain is pain characterized by a changed
nociception In physiology, nociception , also nocioception; ) is the Somatosensory system, sensory nervous system's process of encoding Noxious stimulus, noxious stimuli. It deals with a series of events and processes required for an organism to receive a pai ...
(but without evidence of real or threatened tissue damage, or without disease or damage in the
somatosensory system The somatosensory system, or somatic sensory system is a subset of the sensory nervous system. The main functions of the somatosensory system are the perception of external stimuli, the perception of internal stimuli, and the regulation of bod ...
).


Psychogenic

Psychogenic pain, also called ''psychalgia'' or ''somatoform pain'', is pain caused, increased or prolonged by mental, emotional or behavioral factors. Headaches, back pain and stomach pain are sometimes diagnosed as psychogenic. Those affected are often stigmatized, because both medical professionals and the general public tend to think that pain from a psychological source is not "real". However, specialists consider that it is no less actual or hurtful than pain from any other source."International Association for the Study of Pain , Pain Definitions".
Retrieved 12 October 2010. People with long-term pain frequently display psychological disturbance, with elevated scores on the
Minnesota Multiphasic Personality Inventory The Minnesota Multiphasic Personality Inventory (MMPI) is a standardized psychometric test of adult personality and psychopathology. A version for adolescents also exists, the MMPI-A, and was first published in 1992. Psychologists and other ment ...
scales of
hysteria Hysteria is a term used to mean ungovernable emotional excess and can refer to a temporary state of mind or emotion. In the nineteenth century, female hysteria was considered a diagnosable physical illness in women. It is assumed that the bas ...
, depression and
hypochondriasis Hypochondriasis or hypochondria is a condition in which a person is excessively and unduly worried about having a serious illness. Hypochondria is an old concept whose meaning has repeatedly changed over its lifespan. It has been claimed that th ...
(the " neurotic triad"). Some investigators have argued that it is this neuroticism that causes acute pain to turn chronic, but clinical evidence points in the other direction, to chronic pain causing
neuroticism Neuroticism is a personality trait associated with negative emotions. It is one of the Big Five traits. Individuals with high scores on neuroticism are more likely than average to experience such feelings as anxiety, worry, fear, anger, shame ...
. When long-term pain is relieved by therapeutic intervention, scores on the neurotic triad and
anxiety Anxiety is an emotion characterised by an unpleasant state of inner wikt:turmoil, turmoil and includes feelings of dread over Anticipation, anticipated events. Anxiety is different from fear in that fear is defined as the emotional response ...
fall, often to normal levels.
Self-esteem Self-esteem is confidence in one's own worth, abilities, or morals. Self-esteem encompasses beliefs about oneself (for example, "I am loved", "I am worthy") as well as emotional states, such as triumph, despair, pride, and shame. Smith and Macki ...
, often low in chronic pain patients, also shows improvement once pain has resolved.


Management

Pain can be treated through a variety of methods. The most appropriate method depends upon the situation. Management of
chronic pain Chronic pain is pain that persists or recurs for longer than 3 months.https://icd.who.int/browse/2025-01/mms/en#1581976053 It is also known as gradual burning pain, electrical pain, throbbing pain, and nauseating pain. This type of pain is in cont ...
can be difficult and may require the coordinated efforts of a
pain management Pain management is an aspect of medicine and health care involving relief of pain (pain relief, analgesia, pain control) in various dimensions, from acute (medicine), acute and simple to chronic condition, chronic and challenging. Most physici ...
team, which typically includes
medical practitioner A physician, medical practitioner (British English), medical doctor, or simply doctor is a health professional who practices medicine, which is concerned with promoting, maintaining or restoring health through the study, diagnosis, prognosis ...
s, clinical pharmacists,
clinical psychologist Clinical psychology is an integration of human science, behavioral science, theory, and clinical knowledge for the purpose of understanding, preventing, and relieving psychologically-based distress or dysfunction and to promote subjective well ...
s,
physiotherapist Physical therapy (PT), also known as physiotherapy, is a healthcare profession, as well as the care provided by physical therapists who promote, maintain, or restore health through patient education, physical intervention, disease preventio ...
s,
occupational therapist Occupational therapists (OTs) are health care professionals specializing in occupational therapy and occupational science. OTs and occupational therapy assistants (OTAs) use evidence-based practice, scientific bases and a Holism, holistic perspec ...
s,
physician assistant A physician assistant or physician associate (PA) is a type of non-physician practitioner. While these job titles are used internationally, there is significant variation in training and scope of practice from country to country, and sometimes be ...
s, and
nurse practitioner A nurse practitioner (NP) is an advanced practice registered nurse and a type of mid-level practitioner. NPs are trained to assess patient needs, order and interpret diagnostic and laboratory tests, diagnose disease, prescribe medications an ...
s. Inadequate treatment of pain is widespread throughout surgical wards,
intensive care units An intensive care unit (ICU), also known as an intensive therapy unit or intensive treatment unit (ITU) or critical care unit (CCU), is a special department of a hospital or health care facility that provides intensive care medicine. An inten ...
, and accident and
emergency departments An emergency department (ED), also known as an accident and emergency department (A&E), emergency room (ER), emergency ward (EW) or casualty department, is a medical treatment facility specializing in emergency medicine, the acute care of pat ...
, in
general practice General practice is personal, family, and community-orientated comprehensive primary care that includes diagnosis, continues over time and is anticipatory as well as responsive. Definitions A general practitioner (GP) is a doctor who is a consu ...
, in the management of all forms of chronic pain including cancer pain, and in end of life care. This neglect extends to all ages, from newborns to medically frail elderly. In the US, African and
Hispanic Americans Hispanic and Latino Americans are Americans who have a Spaniards, Spanish or Latin Americans, Latin American background, culture, or family origin. This demographic group includes all Americans who identify as Hispanic or Latino (demonym), ...
are more likely than others to suffer unnecessarily while in the care of a physician; and women's pain is more likely to be undertreated than men's. The
International Association for the Study of Pain The International Association for the Study of Pain (IASP) is an international learned society promoting research, education, and policies for the understanding, prevention, and treatment of pain. IASP was founded in 1973 under the leadership of ...
advocates that the relief of pain should be recognized as a
human right Human rights are universally recognized moral principles or norms that establish standards of human behavior and are often protected by both national and international laws. These rights are considered inherent and inalienable, meaning t ...
, that chronic pain should be considered a disease in its own right, and that
pain medicine Pain management is an aspect of medicine and health care involving relief of pain (pain relief, analgesia, pain control) in various dimensions, from acute and simple to chronic and challenging. Most physicians and other health professionals ...
should have the full status of a
medical specialty A medical specialty is a branch of medical practice that is focused on a defined group of patients, diseases, skills, or philosophy. Examples include those branches of medicine that deal exclusively with children (pediatrics), cancer (oncology), ...
. It is a specialty only in China and Australia at this time. Elsewhere, pain medicine is a subspecialty under disciplines such as
anesthesiology Anesthesiology, anaesthesiology or anaesthesia is the medical specialty concerned with the total perioperative medicine, perioperative care of patients before, during and after surgery. It encompasses anesthesia, intensive care medicine, critica ...
,
physiatry Physical medicine and rehabilitation (PM&R), also known as physiatry, and outside the United States as physical and rehabilitation medicine (PRM), is a branch of medicine that aims to enhance and restore functional ability and quality of life ...
,
neurology Neurology (from , "string, nerve" and the suffix wikt:-logia, -logia, "study of") is the branch of specialty (medicine) , medicine dealing with the diagnosis and treatment of all categories of conditions and disease involving the nervous syst ...
, palliative medicine and
psychiatry Psychiatry is the medical specialty devoted to the diagnosis, treatment, and prevention of deleterious mental disorder, mental conditions. These include matters related to cognition, perceptions, Mood (psychology), mood, emotion, and behavior. ...
. In 2011,
Human Rights Watch Human Rights Watch (HRW) is an international non-governmental organization that conducts research and advocacy on human rights. Headquartered in New York City, the group investigates and reports on issues including War crime, war crimes, crim ...
alerted that tens of millions of people worldwide are still denied access to inexpensive medications for severe pain.


Medication

Acute pain is usually managed with medications such as
analgesic An analgesic drug, also called simply an analgesic, antalgic, pain reliever, or painkiller, is any member of the group of drugs used for pain management. Analgesics are conceptually distinct from anesthetics, which temporarily reduce, and in s ...
s and
anesthetic An anesthetic (American English) or anaesthetic (British English; see spelling differences) is a drug used to induce anesthesia ⁠— ⁠in other words, to result in a temporary loss of sensation or awareness. They may be divided into t ...
s.
Caffeine Caffeine is a central nervous system (CNS) stimulant of the methylxanthine chemical classification, class and is the most commonly consumed Psychoactive drug, psychoactive substance globally. It is mainly used for its eugeroic (wakefulness pr ...
when added to pain medications such as
ibuprofen Ibuprofen is a nonsteroidal anti-inflammatory drug (NSAID) that is used to relieve pain, fever, and inflammation. This includes dysmenorrhea, painful menstrual periods, migraines, and rheumatoid arthritis. It can be taken oral administration, ...
, may provide some additional benefit.
Ketamine Ketamine is a cyclohexanone-derived general anesthetic and NMDA receptor antagonist with analgesic and hallucinogenic properties, used medically for anesthesia, depression, and pain management. Ketamine exists as its S- (esketamine) a ...
can be used instead of opioids for short-term pain. Pain medications can cause paradoxical side effects, such as opioid-induced hyperalgesia (severe generalized pain caused by long-term opioid use). Sugar (
sucrose Sucrose, a disaccharide, is a sugar composed of glucose and fructose subunits. It is produced naturally in plants and is the main constituent of white sugar. It has the molecular formula . For human consumption, sucrose is extracted and refined ...
) when taken by mouth reduces pain in newborn babies undergoing some medical procedures (a lancing of the heel,
venipuncture In medicine, venipuncture or venepuncture is the process of obtaining intravenous access for the purpose of venous Sampling (medicine)#blood, blood sampling (also called ''phlebotomy'') or intravenous therapy. In healthcare, this procedure is p ...
, and
intramuscular injections Intramuscular injection, often abbreviated IM, is the medical injection, injection of a substance into a muscle. In medicine, it is one of several methods for parenteral, parenteral administration of medications. Intramuscular injection may be ...
). Sugar does not remove pain from
circumcision Circumcision is a procedure that removes the foreskin from the human penis. In the most common form of the operation, the foreskin is extended with forceps, then a circumcision device may be placed, after which the foreskin is excised. T ...
, and it is unknown if sugar reduces pain for other procedures. Sugar did not affect pain-related
electrical activity Electricity is the set of physical phenomena associated with the presence and motion of matter possessing an electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwel ...
in the brains of newborns one second after the heel lance procedure. Sweet liquid by mouth moderately reduces the rate and duration of crying caused by immunization injection in children between one and twelve months of age.


Psychological

Individuals with more
social support Social support is the perception and actuality that one is cared for, has assistance available from other people, and, most popularly, that one is part of a supportive social network. These supportive resources can be emotional (e.g., nurturance), ...
experience less cancer pain, take less pain medication, report less labor pain and are less likely to use
epidural anesthesia Epidural administration (from Ancient Greek ἐπί, "upon" + '' dura mater'') is a method of medication administration in which a medicine is injected into the epidural space around the spinal cord. The epidural route is used by physicians a ...
during childbirth, or suffer from chest pain after
coronary artery bypass surgery Coronary artery bypass surgery, also known as coronary artery bypass graft (CABG, pronounced "cabbage"), is a surgical procedure to treat coronary artery disease (CAD), the buildup of plaques in the arteries of the heart. It can relieve chest ...
.
Suggestion Suggestion is the psychological process by which a person guides their own or another person's desired thoughts, feelings, and behaviors by presenting stimuli that may elicit them as reflexes instead of relying on conscious effort. Nineteenth-cent ...
can significantly affect pain intensity. About 35% of people report marked relief after receiving a saline injection they believed to be
morphine Morphine, formerly also called morphia, is an opiate that is found naturally in opium, a dark brown resin produced by drying the latex of opium poppies (''Papaver somniferum''). It is mainly used as an analgesic (pain medication). There are ...
. This
placebo A placebo ( ) can be roughly defined as a sham medical treatment. Common placebos include inert tablets (like sugar pills), inert injections (like saline), sham surgery, and other procedures. Placebos are used in randomized clinical trials ...
effect is more pronounced in people who are prone to anxiety, and so anxiety reduction may account for some of the effect, but it does not account for all of it. Placebos are more effective for intense pain than mild pain; and they produce progressively weaker effects with repeated administration. It is possible for many with chronic pain to become so absorbed in an activity or entertainment that the pain is no longer felt, or is greatly diminished. A number of meta-analyses have found clinical hypnosis to be effective in controlling pain associated with diagnostic and surgical procedures in both adults and children, as well as pain associated with cancer and childbirth. A 2007 review of 13 studies found evidence for the efficacy of hypnosis in the reduction of chronic pain under some conditions, though the number of patients enrolled in the studies was low, raising issues related to the statistical power to detect group differences, and most lacked credible controls for placebo or expectation. The authors concluded that "although the findings provide support for the general applicability of hypnosis in the treatment of chronic pain, considerably more research will be needed to fully determine the effects of hypnosis for different chronic-pain conditions."


Alternative medicine

An analysis of the 13 highest quality studies of pain treatment with
acupuncture Acupuncture is a form of alternative medicine and a component of traditional Chinese medicine (TCM) in which thin needles are inserted into the body. Acupuncture is a pseudoscience; the theories and practices of TCM are not based on scientif ...
, published in January 2009, concluded there was little difference in the effect of real, fake and no acupuncture. However, more recent reviews have found some benefit. Additionally, there is tentative evidence for a few herbal medicines. For chronic (long-term)
lower back pain Low back pain or wiktionary:lumbago#Etymology, lumbago is a common musculoskeletal disorders, disorder involving the muscles, nerves, and bones of the back, in between the lower edge of the ribs and the lower fold of the buttocks. Pain can var ...
,
spinal manipulation Spinal manipulation is an intervention performed on synovial joints of the spine, including the z-joints, the atlanto-occipital, atlanto-axial, lumbosacral, sacroiliac, costotransverse and costovertebral joints. It is typically applied w ...
produces tiny, clinically insignificant, short-term improvements in pain and function, compared with
sham therapy A placebo ( ) can be roughly defined as a sham medical treatment. Common placebos include inert tablets (like sugar pills), inert injections (like saline), sham surgery, and other procedures. Placebos are used in randomized clinical trials to ...
and other interventions. Spinal manipulation produces the same outcome as other treatments, such as general practitioner care, pain-relief drugs, physical therapy, and exercise, for acute (short-term) lower back pain. There has been some interest in the relationship between
vitamin D Vitamin D is a group of structurally related, fat-soluble compounds responsible for increasing intestinal absorption of calcium, magnesium, and phosphate, along with numerous other biological functions. In humans, the most important compo ...
and pain, but the evidence so far from
controlled trials Clinical trials are prospective biomedical or behavioral research studies on human participants designed to answer specific questions about biomedical or behavioral interventions, including new treatments (such as novel vaccines, drugs, dietar ...
for such a relationship, other than in
osteomalacia Osteomalacia is a disease characterized by the softening of the bones caused by impaired bone metabolism primarily due to inadequate levels of available phosphate, calcium, and vitamin D, or because of resorption of calcium. The impairment of b ...
, is inconclusive. The International Association for the Study of Pain (IASP) says that due to a lack of evidence from high quality research, it does not endorse the general use of cannabinoids to treat pain.


Epidemiology

Pain is the main reason for visiting an
emergency department An emergency department (ED), also known as an accident and emergency department (A&E), emergency room (ER), emergency ward (EW) or casualty department, is a medical treatment facility specializing in emergency medicine, the Acute (medicine), ...
in more than 50% of cases, and is present in 30% of family practice visits. Several
epidemiological Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and Risk factor (epidemiology), determinants of health and disease conditions in a defined population, and application of this knowledge to prevent dise ...
studies have reported widely varying prevalence rates for chronic pain, ranging from 12 to 80% of the population. It becomes more common as people approach death. A study of 4,703 patients found that 26% had pain in the last two years of life, increasing to 46% in the last month. A survey of 6,636 children (0–18 years of age) found that, of the 5,424 respondents, 54% had experienced pain in the preceding three months. A quarter reported having experienced recurrent or continuous pain for three months or more, and a third of these reported frequent and intense pain. The intensity of chronic pain was higher for girls, and girls' reports of chronic pain increased markedly between ages 12 and 14.


Society and culture

Physical pain is a universal experience, and a strong motivator of human and animal behavior. As such, physical pain is used politically in relation to various issues such as
pain management Pain management is an aspect of medicine and health care involving relief of pain (pain relief, analgesia, pain control) in various dimensions, from acute (medicine), acute and simple to chronic condition, chronic and challenging. Most physici ...
policy, drug control, 
animal rights Animal rights is the philosophy according to which many or all Animal consciousness, sentient animals have Moral patienthood, moral worth independent of their Utilitarianism, utility to humans, and that their most basic interests—such as ...
or 
animal welfare Animal welfare is the quality of life and overall well-being of animals. Formal standards of animal welfare vary between contexts, but are debated mostly by animal welfare groups, legislators, and academics. Animal welfare science uses measures ...
, 
torture Torture is the deliberate infliction of severe pain or suffering on a person for reasons including corporal punishment, punishment, forced confession, extracting a confession, interrogational torture, interrogation for information, or intimid ...
, and
pain compliance Pain compliance is the use of painful stimulus to control or direct a person. The purpose of pain compliance is to direct the actions of the subject, and to this end, the pain is lessened or removed when compliance is achieved. This provides incen ...
. The deliberate infliction of pain and the medical management of pain are both important aspects of
biopower Biopower (or ''biopouvoir'' in French), coined by French social theorist Michel Foucault, refers to various means by which modern nation states control of populations, control their populations. In Foucault's work, it has been used to refer ...
, a concept that encompasses the "set of mechanisms through which the basic biological features of the human species became the object of a political strategy". In various contexts, the deliberate infliction of pain in the form of
corporal punishment A corporal punishment or a physical punishment is a punishment which is intended to cause physical pain to a person. When it is inflicted on Minor (law), minors, especially in home and school settings, its methods may include spanking or Padd ...
is used as retribution for an offence, for the purpose of disciplining or reforming a wrongdoer, or to deter attitudes or behaviour deemed unacceptable. In Western societies, the intentional infliction of severe pain (torture) was principally used to extract confession prior to its abolition in the latter part of the 19th century. Torture as a means to punish the
citizen Citizenship is a membership and allegiance to a sovereign state. Though citizenship is often conflated with nationality in today's English-speaking world, international law does not usually use the term ''citizenship'' to refer to nationality ...
has been reserved for offences posing a severe threat to the social fabric (for example,
treason Treason is the crime of attacking a state (polity), state authority to which one owes allegiance. This typically includes acts such as participating in a war against one's native country, attempting to Coup d'état, overthrow its government, spy ...
). The administration of torture on bodies othered by the cultural narrative, those observed as not 'full members of society' met a resurgence in the 20th century, possibly due to the heightened warfare. Many cultures use painful ritual practices as a catalyst for psychological transformation. The use of pain to transition to a 'cleansed and purified' state is seen in religious
self-flagellation Self-flagellation is the disciplinary and devotional practice of Flagellation, flogging oneself with whips or other instruments that inflict pain. In Christianity, self-flagellation is practiced in the context of the doctrine of the mortification ...
practices (particularly those of
Christianity Christianity is an Abrahamic monotheistic religion, which states that Jesus in Christianity, Jesus is the Son of God (Christianity), Son of God and Resurrection of Jesus, rose from the dead after his Crucifixion of Jesus, crucifixion, whose ...
and
Islam Islam is an Abrahamic religions, Abrahamic monotheistic religion based on the Quran, and the teachings of Muhammad. Adherents of Islam are called Muslims, who are estimated to number Islam by country, 2 billion worldwide and are the world ...
), or personal
catharsis Catharsis is from the Ancient Greek word , , meaning "purification" or "cleansing", commonly used to refer to the purification and purgation of thoughts and emotions by way of expressing them. The desired result is an emotional state of renewal an ...
in neo-primitive body suspension experiences. Beliefs about pain play an important role in sporting cultures. Pain may be viewed positively, exemplified by the 'no pain, no gain' attitude, with pain seen as an essential part of training. Sporting culture tends to normalise experiences of pain and injury and celebrate athletes who 'play hurt'. Pain has psychological, social, and physical dimensions, and is greatly influenced by cultural factors.


Non-humans


Animals

René Descartes René Descartes ( , ; ; 31 March 1596 – 11 February 1650) was a French philosopher, scientist, and mathematician, widely considered a seminal figure in the emergence of modern philosophy and Modern science, science. Mathematics was paramou ...
argued that animals lack consciousness and therefore do not experience pain and suffering in the way that humans do.Working party of the Nuffield Council on Bioethics (2005)
"The ethics of research involving animals. London: Nuffield Council on Bioethics."
. Archived from the original on 25 June 2008. Retrieved 12 January 2010. Bernard Rollin of
Colorado State University Colorado State University (Colorado State or CSU) is a Public university, public Land-grant university, land-grant research university in Fort Collins, Colorado, United States. It is the flagship university of the Colorado State University Syst ...
, the principal author of two U.S. federal laws regulating pain relief for animals, wrote that researchers remained unsure into the 1980s as to whether animals experience pain, and that veterinarians trained in the U.S. before 1989 were simply taught to ignore animal pain. cited in The ability of invertebrate species of animals, such as insects, to feel pain and suffering is unclear. Specialists believe that all vertebrates can feel pain, and that certain invertebrates, like the octopus, may also. The presence of pain in animals is unknown, but can be inferred through physical and behavioral reactions, such as paw withdrawal from various noxious mechanical stimuli in rodents.


Plants

While
plants Plants are the eukaryotes that form the kingdom Plantae; they are predominantly photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with cyanobacteria to produce sugars f ...
, as living beings, can perceive and communicate physical stimuli and damage, they do not feel pain simply because of the lack of any pain receptors, nerves, or a brain, and, by extension, a lack of consciousness. Many plants are known to perceive and respond to mechanical stimuli at a cellular level, and some plants such as the
venus flytrap The Venus flytrap (''Dionaea muscipula'') is a carnivorous plant native to the temperate and subtropical wetlands of North Carolina and South Carolina, on the East Coast of the United States. Although various modern hybrids have been created ...
or touch-me-not, are known for their "obvious sensory abilities". Nevertheless, no member of the plant kingdom does feel pain notwithstanding their abilities to respond to sunlight, gravity, wind, and any external stimuli such as insect bites since they lack any nervous system. The primary reason for this is that, unlike the members of the animal kingdom whose evolutionary successes and failures are shaped by suffering, the evolution of plants are simply shaped by life and death.


See also

*
Feeling According to the '' APA Dictionary of Psychology'', a feeling is "a self-contained phenomenal experience"; feelings are "subjective, evaluative, and independent of the sensations, thoughts, or images evoking them". The term ''feeling'' is closel ...
, a perceptual state of conscious experience. *
Hedonic adaptation The hedonic treadmill, also known as hedonic adaptation, is the observed tendency of humans to quickly return to a relatively stable level of happiness (or sadness) despite major positive or negative events or life changes. According to this the ...
, the tendency to quickly return to a relatively stable level of happiness despite major positive or negative events * Pain (philosophy), the branch of philosophy concerned with suffering and physical pain *
Pain and suffering Pain and suffering is the legal term for the physical and emotional stress caused from an injury (see also pain and suffering). Some damages that might come under this category would be: aches, temporary and permanent limitations on activity, ...
, the legal term for the physical and emotional stress caused from an injury


Explanatory notes


References


Further reading

* * Allison Parshall, "Pain Language: The sound of 'ow' transcends borders", ''
Scientific American ''Scientific American'', informally abbreviated ''SciAm'' or sometimes ''SA'', is an American popular science magazine. Many scientists, including Albert Einstein and Nikola Tesla, have contributed articles to it, with more than 150 Nobel Pri ...
'', vol. 332, no. 2 (February 2025), pp. 16–18. "Many
language Language is a structured system of communication that consists of grammar and vocabulary. It is the primary means by which humans convey meaning, both in spoken and signed language, signed forms, and may also be conveyed through writing syste ...
s have an
interjection An interjection is a word or expression that occurs as an utterance on its own and expresses a spontaneous feeling, situation or reaction. It is a diverse category, with many different types, such as exclamations ''(ouch!'', ''wow!''), curses (''da ...
word for expressing pain. atarzyna Pisanski ''et al.'', writing in the ''Journal of the Acoustical Society of America'', have">Journal of the Acoustical Society of America">atarzyna Pisanski ''et al.'', writing in the ''Journal of the Acoustical Society of America'', havefound that pain interjections tend to contain the vowel sound 'ah' (written as [a] in the International Phonetic Alphabet) and letter combinations that incorporate it, such as 'ow' and 'ai.' These patterns may point back to the origins of human language itself." (p. 16.) "Researchers are continually discovering cases of
symbolism Symbolism or symbolist may refer to: *Symbol, any object or sign that represents an idea Arts *Artistic symbol, an element of a literary, visual, or other work of art that represents an idea ** Color symbolism, the use of colors within various c ...
, or sound
iconicity In functional- cognitive linguistics, as well as in semiotics, iconicity is the conceived similarity or analogy between the form of a sign (linguistic or otherwise) and its meaning, as opposed to arbitrariness (which is typically assumed i ...
, in which a word's intrinsic nature has some connection to its meaning. These cases run counter to decades of
linguistic theory Theoretical linguistics is a term in linguistics that, like the related term general linguistics, can be understood in different ways. Both can be taken as a reference to the theory of language, or the branch of linguistics that inquires into the ...
, which had regarded language as fundamentally arbitrary... onomatopoeically imitate a sound. Also">onomatopoeia.html" ;"title="any words onomatopoeia">onomatopoeically imitate a sound. Alsothere's the Bouba/kiki effect">'bouba-kiki' effect, whereby people from varying cultures are more likely to associate the nonsense word 'bouba' with a rounded shape and 'kiki' with a spiked one.... [S]omehow we all have a ''feeling'' about this,' says Aleksandra Ćwiek... [She and her colleagues have] show[n] that people associate the Trill consonant, trilled 'R' sound with roughness and the 'L' sound with smoothness.
Mark Dingemanse Mark Dingemanse (Middelburg, Zeeland, the Netherlands, 1983) is a Dutch linguist. He is an associate professor in Language and Communication at the Centre for Language Studies of Radboud University Nijmegen. He is also a Senior Investigator in th ...
... in 2013 found
hat A hat is a Headgear, head covering which is worn for various reasons, including protection against weather conditions, ceremonial reasons such as university graduation, religious reasons, safety, or as a fashion accessory. Hats which incorpor ...
the conversational 'Huh?' and similar words in other languages may be universal." (p. 18.)


External links


"Pain"
''
Stanford Encyclopedia of Philosophy The ''Stanford Encyclopedia of Philosophy'' (''SEP'') is a freely available online philosophy resource published and maintained by Stanford University, encompassing both an online encyclopedia of philosophy and peer-reviewed original publication ...
'' {{Authority control Acute pain Nociception Sensory systems Suffering Symptoms and signs