Pain is a distressing feeling often caused by intense or damaging stimuli. 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 emotional experience associated with, or resembling that associated with, actual or potential tissue damage." In medical diagnosis, pain is regarded as a

symptom Signs and symptoms are the observed or detectable signs, and experienced symptoms of an illness, injury, or condition. A sign for example may be a higher or lower temperature than normal, raised or lowered blood pressure or an abnormality showin ...

of an underlying condition. Pain motivates the individual to withdraw from damaging situations, to protect a damaged body part while it heals, and to avoid similar experiences in the future. 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 as f ...

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. 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 psycho-social intervention that aims to reduce symptoms of various mental health conditions, primarily depression and anxiety disorders. CBT focuses on challenging and changing cognitive distortions (suc ...

, excitement, or distraction can affect pain's intensity or unpleasantness. In some debates regarding

physician-assisted suicide Assisted suicide is suicide undertaken with the aid of another person. The term usually refers to physician-assisted suicide (PAS), which is suicide that is assisted by a physician or other healthcare provider. Once it is determined that the p ...

euthanasia Euthanasia (from el, εὐθανασία 'good death': εὖ, ''eu'' 'well, good' + θάνατος, ''thanatos'' 'death') is the practice of intentionally ending life to eliminate pain and suffering. Different countries have different eut ...

, pain has been used as an argument to permit people who are terminally ill to end their lives.

Etymology

First attested in English in 1297, the word ''peyn'' comes from the

Old French Old French (, , ; Modern French: ) was the language spoken in most of the northern half of France from approximately the 8th to the 14th centuries. Rather than a unified language, Old French was a linkage of Romance dialects, mutually intelligib ...

''peine'', in turn from

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

''poena'' meaning "punishment, penalty" (also meaning "torment, hardship, suffering" in Late Latin) and that from

Greek Greek may refer to: Greece 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 ...

ποινή (''poine''), generally meaning "price paid, penalty, punishment".

Classification

The

recommends using specific features to describe a patient's pain: # region of the body involved (e.g. abdomen, lower limbs), # system whose dysfunction may be causing the pain (e.g., nervous, gastrointestinal), # duration and pattern of occurrence, # intensity, and # 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 joints. It typically results in warm, swollen, and painful joints. Pain and stiffness often worsen following rest. Most commonly, the wrist and hands are involv ...

peripheral neuropathy Peripheral neuropathy, often shortened to neuropathy, is a general term describing disease affecting the peripheral nerves, meaning nerves beyond the brain and spinal cord. Damage to peripheral nerves may impair sensation, movement, gland, or or ...

cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...

and

idiopathic An idiopathic disease is any disease with an unknown cause or mechanism of apparent wikt:spontaneous, spontaneous origin. From Ancient Greek, Greek ἴδιος ''idios'' "one's own" and πάθος ''pathos'' "suffering", ''idiopathy'' means approxi ...

pain, may persist for years. Pain that lasts a long time is called " chronic" or "persistent", and pain that resolves quickly is called "

acute Acute may refer to: Science and technology * Acute angle ** Acute triangle ** Acute, a leaf shape in the glossary of leaf morphology * Acute (medicine), a disease that it is of short duration and of recent onset. ** Acute toxicity, the adverse eff ...

". 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 more than 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, bad sunburn can cause temporary allodynia, and touching sunburned skin, or running cold or warm water over it, can be very painful. It i ...

is pain experienced in response to a normally painless stimulus. It has no biological function and is classified by stimuli into dynamic mechanical, punctate and static.

Phantom

Phantom pain Phantom pain is a perception that an individual experiences relating to a limb or an organ that is not physically part of the body, either because it was removed or was never there in the first place. However, phantom limb sensations can also oc ...

is pain felt in a part of the body that has been

amputated Amputation is the removal of a limb 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 carried out on indivi ...

, 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 a long period, parts of the intact body may become sensitized, so that touching them evokes pain in the phantom limb. Phantom limb pain may accompany

urination Urination, also known as micturition, is the release of urine from the urinary bladder through the urethra to the outside of the body. It is the urinary system's form of excretion. It is also known medically as micturition, voiding, uresis, ...

defecation Defecation (or defaecation) follows digestion, and is a necessary process by which organisms eliminate a solid, semisolid, or liquid waste material known as feces from the digestive tract via the anus. The act has a variety of names ranging f ...

Local anesthetic A local anesthetic (LA) is a medication that causes absence of pain sensation. In the context of surgery, a local anesthetic creates an absence of pain in a specific location of the body without a loss of consciousness, as opposed to a general an ...

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 membrane- ...

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 neural ...

, the loss of sensation and voluntary motor control after serious spinal cord damage, may be accompanied by

girdle pain Pelvic girdle pain (abbreviated PGP) can be described as a pregnancy discomfort for some women and a severe disability for others. PGP can cause pain, instability and limitation of mobility and functioning in any of the three pelvic joints. PGP ha ...

at the level of the spinal cord damage,

visceral pain Visceral pain is pain that results from the activation of nociceptors of the thoracic, pelvic, or abdominal viscera (organs). Visceral structures are highly sensitive to distension (stretch), ischemia and inflammation, but relatively insensitive to ...

evoked by a filling bladder or bowel, or, in five to ten per cent of paraplegics, 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 be immediate or may not occur until 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 and simple to chronic and challenging. Most physicians and other health professionals pr ...

. 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) pa ...

vary from person to person and according to the cause. Management of breakthrough pain can entail intensive use of

opioid Opioids are substances that act on opioid receptors to produce morphine-like effects. Medically they are primarily used for pain relief, including anesthesia. Other medical uses include suppression of diarrhea, replacement therapy for opioid us ...

s, including

fentanyl Fentanyl, also spelled fentanil, is a very potent synthetic opioid used as a pain medication. Together with other drugs, fentanyl is used for anesthesia. It is also used illicitly as a recreational drug, sometimes mixed with heroin, cocaine ...

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 to induce a state described as intense pain devoid of unpleasantness in some patients, with

morphine Morphine is a strong opiate that is found naturally in opium, a dark brown resin in poppies (''Papaver somniferum''). It is mainly used as a analgesic, pain medication, and is also commonly used recreational drug, recreationally, or to make ...

injection or psychosurgery. Such patients report that they have 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 highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes 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. Symptoms may include loss of muscle function, sensation, or autonomic function in the parts of the body served by the spinal cor ...

diabetes mellitus Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ap ...

(

diabetic neuropathy Diabetic neuropathy is various types of nerve damage associated with diabetes mellitus. Symptoms depend on the site of nerve damage and can include motor changes such as weakness; sensory symptoms such as numbness, tingling, or pain; or autonomic c ...

), or

leprosy Leprosy, also known as Hansen's disease (HD), is a long-term infection by the bacteria ''Mycobacterium leprae'' or ''Mycobacterium lepromatosis''. Infection can lead to damage of the nerves, respiratory tract, skin, and eyes. This nerve damag ...

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 one or more extraordinarily rare conditions in which a person cannot feel (and has never felt) physical pain. The conditions described here are separate from the HSAN ...

". 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 neurons ...

and

congenital insensitivity to pain with anhidrosis Congenital insensitivity to pain with anhidrosis (CIPA) is a rare autosomal recessive disorder of the nervous system which prevents the feeling of pain or temperature, and prevents a person from sweating. Cognitive disorders are commonly coinciden ...

). These conditions feature decreased sensitivity to pain together with other neurological abnormalities, particularly of the

autonomic nervous system The autonomic nervous system (ANS), formerly referred to as the vegetative nervous system, is a division of the peripheral nervous system that supplies viscera, internal organs, smooth muscle and glands. The autonomic nervous system is a control ...

. A very rare syndrome with isolated congenital insensitivity to pain has been linked with mutations in the ''

SCN9A 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 dorsal root ganglion (DRG) and trigeminal ganglion and sympatheti ...

'' gene, which codes for a sodium channel ( Na_v1.7) 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 Working memory is a cognitive system with a limited capacity that can 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 memory, ...

, mental flexibility, problem solving, and information processing speed. Acute and chronic pain are 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 A meta-analysis is a statistical analysis that combines the results of multiple scientific studies. Meta-analyses can be performed when there are multiple scientific studies addressing the same question, with each individual study reporting me ...

which summarized and evaluated numerous studies from various psychological disciplines, found a reduction in

negative affect 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, contempt, disgust, g ...

. 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 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 Richard Sol ...

Theory

Historical

Before the relatively recent discovery of

neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. N ...

s and their role in pain, various different body functions were proposed to account for pain. There were several competing early theories of pain among the ancient Greeks:

Hippocrates Hippocrates of Kos (; grc-gre, Ἱπποκράτης ὁ Κῷος, Hippokrátēs ho Kôios; ), also known as Hippocrates II, was a Greek physician of the classical period who is considered one of the most outstanding figures in the history of ...

believed that it was due to an imbalance in

vital fluid Vitalism is a belief that starts from the premise that "living organisms are fundamentally different from non-living entities because they contain some non-physical element or are governed by different principles than are inanimate things." Wher ...

s.Linton. Models of Pain Perception. Elsevier Health, 2005. Print. In the 11th century,

Avicenna Ibn Sina ( fa, ابن سینا; 980 – June 1037 CE), commonly known in the West as Avicenna (), was a Persian polymath who is regarded as one of the most significant physicians, astronomers, philosophers, and writers of the Islamic G ...

theorized that there were a number of feeling senses including touch, pain and titillation. Jan Baptist Weenix - Portrait of René Descartes

In 1644,

René Descartes René Descartes ( or ; ; Latinized: Renatus Cartesius; 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 science. Mathem ...

theorized that pain was a disturbance that passed along nerve fibers until the disturbance reached the brain. Descartes's work, along with Avicenna's, 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 mostly by physiologists and physicians, and the intensive theory was mostly backed by psychologists. 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 psychiatrist ...

and experiments by

Max von Frey Maximilian (Max) Ruppert Franz von Frey (16 November 1852 – 25 January 1932) was an Austrian-German physiologist who was born in Salzburg. He received his doctorate from the University of Leipzig in 1877, and subsequently worked at Carl Ludwig's ...

, the psychologists migrated to specificity almost en masse, and by century's end, most textbooks on physiology and psychology were presenting pain specificity as fact.

Modern

Schematic of cortical areas involved with pain processing and fMRI

Some sensory fibers do not differentiate between noxious and non-noxious stimuli, while others,

nociceptor A nociceptor ("pain receptor" from Latin ''nocere'' 'to harm or hurt') 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 sens ...

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 In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The ''IEEE Transactions on Signal Processing'' ...

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 the flow of io ...

s it expresses at its peripheral end. Dozens of different types of nociceptor ion channels have so far 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 is a lipid-rich material that surrounds nerve cell axons (the nervous system's "wires") to insulate them and increase the rate at which electrical impulses (called action potentials) are passed along the axon. The myelinated axon can be ...

), 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 o ...

and connect with spinal cord nerve fibers in the central gelatinous substance of the spinal cord. 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 carryi ...

and ascend in the

spinothalamic tract The spinothalamic tract is a part of the anterolateral system or the ventrolateral system, a sensory pathway to the thalamus. From the ventral posterolateral nucleus in the thalamus, sensory information is relayed upward to the somatosensory cor ...

. Before reaching the brain, the spinothalamic tract splits into the

lateral Lateral is a geometric term of location which may refer to: Healthcare *Lateral (anatomy), an anatomical direction *Lateral cricoarytenoid muscle *Lateral release (surgery), a surgical procedure on the side of a kneecap Phonetics *Lateral cons ...

neospinothalamic tract Nociception (also nocioception, from Latin ''nocere'' 'to harm or hurt') is the sensory nervous system's process of encoding noxious stimuli. It deals with a series of events and processes required for an organism to receive a painful stimulus, co ...

and the medial,

paleospinothalamic tract Nociception (also nocioception, from Latin ''nocere'' 'to harm or hurt') is the sensory nervous system's process of encoding noxious stimuli. It deals with a series of events and processes required for an organism to receive a painful stimulus, co ...

. The neospinothalamic tract carries the fast, sharp A-delta signal to the ventral posterolateral nucleus of the

thalamus The thalamus (from Greek θάλαμος, "chamber") is a large mass of gray matter located in the dorsal part of the diencephalon (a division of the forebrain). Nerve fibers project out of the thalamus to the cerebral cortex in all directions, ...

. 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 and frontal lobes) within each hemisphere of the mammalian bra ...

(thought to embody, among other things, the feeling that distinguishes pain from other

homeostatic emotion Homeostatic feeling (or homeostatic affect, or homeostatic emotion, or primordial emotion) is a class of feelings (e.g., thirst, pain, fatigue) evoked by an internal body state. Some homeostatic feelings drive specific behavior (drinking, with ...

s such as itch and nausea) and

anterior cingulate cortex In the human brain, 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 primary and

secondary Secondary may refer to: Science and nature * Secondary emission, of particles ** Secondary electrons, electrons generated as ionization products * The secondary winding, or the electrical or electronic circuit connected to the secondary winding i ...

somatosensory cortex. 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

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 of pain. The basic concept is that non-painful stimuli block the pathways for painful sti ...

s, respond to A-delta and C fibers, but also to 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 revolutionized pain research by introducing the gate control theory of pain. ...

and

Patrick Wall Sir Patrick Henry Bligh Wall, (14 October 1916 – 15 May 1998) was a British commando in the Royal Marines during the Second World War and later a Conservative Party politician. He was the Member of Parliament (MP) for Haltemprice in the Eas ...

introduced their gate control theory 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 and

Kenneth Casey Kenneth Casey (January 10, 1899 – August 10, 1965) was an American composer, publisher, author, and child movie star in early silents. Biography Born in New York City, Casey worked as a child actor in over thirty films for Vitagraph Studios b ...

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

have reduced

life expectancy Life expectancy is a statistical measure of the average time an organism is expected to live, based on the year of its birth, current age, and other demographic factors like sex. The most commonly used measure is life expectancy at birth ...

. In '' The Greatest Show on Earth: The Evidence for Evolution'', biologist

Richard Dawkins Richard Dawkins (born 26 March 1941) is a British evolutionary biologist and author. He is an emeritus fellow of New College, Oxford and was Professor for Public Understanding of Science in the University of Oxford from 1995 to 2008. An ath ...

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 other 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. 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 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 stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge through a surface or into a control volume. The moving pa ...

, 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 w ...

, 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 Margo McCaffery was an American registered nurse and pioneer of the field of pain management nursing Nursing is a profession within the health care sector focused on the care of individuals, families, and communities so they may attain, ma ...

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 McGill University (french: link=no, Université McGill) is an English-language public research university located in M ...

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 (NVC) is the transmission of messages or signals through a nonverbal platform such as eye contact, facial expressions, gestures, posture, and body language. It includes the use of social cues, kinesics, distance ( proxe ...

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, and encompasses any behavior in which one member affects the other. This is due to an interaction among those members. Social behavior can be seen as similar to an ...

and possibly experience a

decreased appetite Anorexia is a medical term for a loss of appetite. While the term in non-scientific publications is often used interchangeably with anorexia nervosa, many possible causes exist for a loss of appetite, some of which may be harmless, while others ...

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. It is also called range of travel (or ROT), particularly when talking about mechanical devices and in mechanic ...

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 A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy (pharmacotherapy) is an important part of the medical field and re ...

. 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 to actively management of illness when it occurs. Individuals engage in some form of self-care daily with food ...

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 occurs by the presence or absence of a Y in the 23rd pair of chromosomes in the human genome. Phenotypic sex refers to an individual's sex as determined by the ...

can be the result of social and cultural expectations, with women expected to be more emotional and show pain, and men more stoic. As a result, female pain is often stigmatized, leading to less urgent treatment of women based on social expectations of their ability to accurately report it. This leads 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 blood flow decreases or stops to the coronary artery of the heart, causing damage to the heart muscle. The most common symptom is chest pain or discomfort which may ...

, 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 severe chest or ...

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 An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action po ...

that respond to stimuli approaching or exceeding harmful intensity (

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 with the symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , and boils to a vi ...

in a cut or chemicals released during

inflammation Inflammation (from la, wikt:en:inflammatio#Latin, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or Irritation, irritants, and is a protective response involving im ...

). 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 wi ...

and

, but relatively insensitive to other stimuli that normally evoke pain in other structures, such as burning and cutting.

Visceral pain Visceral pain is pain that results from the activation of nociceptors of the thoracic, pelvic, or abdominal viscera (organs). Visceral structures are highly sensitive to distension (stretch), ischemia and inflammation, but relatively insensitive to ...

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 (; plural fasciae or fascias; adjective fascial; from Latin: "band") is a band or sheet of connective tissue, primarily collagen, beneath the skin that attaches to, stabilizes, encloses, and separates muscles and other internal organs. ...

e and muscles, and is dull, aching, poorly-localized pain. Examples include

sprain A sprain, also known as a torn ligament, is an acute 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 ...

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)

burn A burn is an injury to skin, or other tissues, caused by heat, cold, electricity, chemicals, friction, or ultraviolet radiation (like sunburn). Most burns are due to heat from hot liquids (called scalding), solids, or fire. Burns occur mainl ...

Neuropathic

Neuropathic pain is caused by damage or disease affecting any part of the

involved in bodily feelings (the

somatosensory system In physiology, the somatosensory system is the network of neural structures in the brain and body that produce the perception of touch (haptic perception), as well as temperature (thermoception), body position (proprioception), and pain. It ...

). Neuropathic pain may be divided into peripheral,

central Central is an adjective usually referring to being in the center of some place or (mathematical) object. Central may also refer to: Directions and generalised locations * Central Africa, a region in the centre of Africa continent, also known as ...

, or mixed (peripheral and central) neuropathic pain.

Peripheral A peripheral or peripheral device is an auxiliary device used to put information into and get information out of a computer. The term ''peripheral device'' refers to all hardware components that are attached to a computer and are controlled by the ...

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, repetitive, nonrhythmic motor movement or vocalization involving discrete muscle groups.American Psychiatric Association (2000)DSM-IV-TR: Tourette's Disorder.''Diagnostic and Statistical Manual of Mental Disorders'', 4th ed., ...

, painful

, 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). Typically, the nerve pain (neuralgia) is confined ...

Nociplastic

Nociplastic pain is pain characterized by a changed

nociception Nociception (also nocioception, from Latin ''nocere'' 'to harm or hurt') is the sensory nervous system's process of encoding noxious stimuli. It deals with a series of events and processes required for an organism to receive a painful stimulus, co ...

(but without evidence of real or threatened tissue damage, or without disease or damage in the

). In some debates regarding

, pain has been used as an argument to permit people who are terminally ill to end their lives.

Psychogenic

Psychogenic pain, also called ''psychalgia'' or ''somatoform pain'', is pain caused, increased or prolonged by mental, emotional or behavioral factors. Headache, 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. Psychologists and other mental health professionals use various versions of the MMPI to help develop treatment ...

scales of

hysteria Hysteria is a term used colloquially to mean ungovernable emotional excess and can refer to a temporary state of mind or emotion. In the nineteenth century, hysteria was considered a diagnosable physical illness in women. It is assumed that ...

, depression and

hypochondriasis Hypochondriasis or hypochondria is a condition in which a person is excessively and unduly worried about having a serious illness. An old concept, the meaning of hypochondria has repeatedly changed. It has been claimed that this debilitating cond ...

(the "

neurotic triad Chronic pain is classified as pain that lasts longer than three to six months. In medicine, the distinction between Acute (medicine), acute and Chronic condition, chronic pain is sometimes determined by the amount of time since onset. Two commonly ...

"). Some investigators have argued that it is this neuroticism that causes acute pain to turn chronic, but clinical evidence points the other direction, to chronic pain causing

neuroticism In the study of psychology, neuroticism has been considered a fundamental personality trait. For example, in the Big Five approach to personality trait theory, individuals with high scores for neuroticism are more likely than average to be moody ...

. When long-term pain is relieved by therapeutic intervention, scores on the neurotic triad and

anxiety Anxiety is an emotion which is characterized by an unpleasant state of inner turmoil and includes feelings of dread over anticipated events. Anxiety is different than fear in that the former is defined as the anticipation of a future threat wh ...

fall, often to normal levels.

Self-esteem Self-esteem is confidence in one's own worth or abilities. 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 Mackie (2007) d ...

, 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 classified as pain that lasts longer than three to six months. In medicine, the distinction between Acute (medicine), acute and Chronic condition, chronic pain is sometimes determined by the amount of time since onset. Two commonly ...

can be difficult and may require the coordinated efforts of a

team, which typically includes

medical practitioner A physician (American English), medical practitioner (Commonwealth English), medical doctor, or simply doctor, is a health professional who practices medicine, which is concerned with promoting, maintaining or restoring health through th ...

s, clinical pharmacists, clinical psychologists,

physiotherapist Physical therapy (PT), also known as physiotherapy, is one of the allied health professions. It is provided by physical therapists who promote, maintain, or restore health through physical examination, diagnosis, management, prognosis, patien ...

occupational therapist Occupational therapists (OTs) are health care professionals specializing in occupational therapy and occupational science. OTs and occupational therapy assistants (OTAs) use scientific bases and a holistic perspective to promote a person's abilit ...

physician assistant A physician assistant or physician associate (PA) is a type of Mid-level practitioner, mid-level health care provider. In North America PAs may diagnose illnesses, develop and manage treatment plans, prescribe medications, and may serve as a pri ...

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, formulate and prescribe m ...

s. Inadequate treatment of pain is widespread throughout surgical wards,

intensive care units 220px, Intensive care unit 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 intensiv ...

, 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 pati ...

, in

general practice General practice is the name given in various nations, such as the United Kingdom, India, Australia, New Zealand and South Africa to the services provided by general practitioners. In some nations, such as the US, similar services may be describe ...

, in the management of all forms of chronic pain including cancer pain, and in

end of life care End-of-life care (EoLC) refers to health care provided in the time leading up to a person's death. End-of-life care can be provided in the hours, days, or months before a person dies and encompasses care and support for a person's mental and emotio ...

. This neglect extends to all ages, from newborns to medically frail elderly. In the US,

African African or Africans may refer to: * Anything from or pertaining to the continent of Africa: ** People who are native to Africa, descendants of natives of Africa, or individuals who trace their ancestry to indigenous inhabitants of Africa *** Ethn ...

and

Hispanic Americans Hispanic and Latino Americans ( es, Estadounidenses hispanos y latinos; pt, Estadunidenses hispânicos e latinos) are Americans of Spaniards, Spanish and/or Latin Americans, Latin American ancestry. More broadly, these demographics include a ...

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

advocates that the relief of pain should be recognized as a

human right Human rights are moral principles or normsJames Nickel, with assistance from Thomas Pogge, M.B.E. Smith, and Leif Wenar, 13 December 2013, Stanford Encyclopedia of PhilosophyHuman Rights Retrieved 14 August 2014 for certain standards of hu ...

, 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 professional ...

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 (paediatrics), 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 care of patients before, during and after surgery. It encompasses anesthesia, intensive care medicine, critical emergency medicine, ...

physiatry Physical medicine and rehabilitation, also known as physiatry, is a branch of medicine that aims to enhance and restore functional ability and quality of life to people with physical impairments or disabilities. This can include conditions su ...

neurology Neurology (from el, wikt:νεῦρον, νεῦρον (neûron), "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 co ...

palliative medicine In 2006, ''hospice and palliative medicine'' was officially recognized by the American Board of Medical Specialties, and is ''co-sponsored'' by the American Boards of * Internal Medicine * Anesthesiology * Family Medicine * Physical Medicine ...

and

psychiatry Psychiatry is the medical specialty devoted to the diagnosis, prevention, and treatment of mental disorders. These include various maladaptations related to mood, behaviour, cognition, and perceptions. See glossary of psychiatry. Initial psych ...

. In 2011,

Human Rights Watch Human Rights Watch (HRW) is an international non-governmental organization, headquartered in New York City, that conducts research and advocacy on human rights. The group pressures governments, policy makers, companies, and individual human r ...

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 (American English), analgaesic (British English), pain reliever, or painkiller, is any member of the group of drugs used to achieve relief from pain (that is, analgesia or pain management). It ...

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 two ...

Caffeine Caffeine is a central nervous system (CNS) stimulant of the methylxanthine class. It is mainly used recreationally as a cognitive enhancer, increasing alertness and attentional performance. Caffeine acts by blocking binding of adenosine t ...

when added to pain medications such as

ibuprofen Ibuprofen is a nonsteroidal anti-inflammatory drug (NSAID) that is used for treating pain, fever, and inflammation. This includes painful menstrual periods, migraines, and rheumatoid arthritis. It may also be used to close a patent ductus arte ...

, may provide some additional benefit.

Ketamine Ketamine is a dissociative anesthetic used medically for induction and maintenance of anesthesia. It is also used as a recreational drug. It is one of the safest anesthetics, as, in contrast with opiates, ether, and propofol, it suppresses ne ...

can be used instead of opioids for short-term pain. Pain medications can cause paradoxical side effects, such as

opioid-induced hyperalgesia Opioid-induced hyperalgesia (OIH) or opioid-induced abnormal pain sensitivity, also called paradoxical hyperalgesia, is generalized pain caused by the long-term use of opioids such as morphine, oxycodone, and methadone. OIH is not necessarily confi ...

(severe 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 blood sampling (also called ''phlebotomy'') or intravenous therapy. In healthcare, this procedure is performed by medical labor ...

, and intramuscular injections). Sugar does not remove pain from

circumcision Circumcision is a surgical procedure, 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 ...

, and it is unknown if sugar reduces pain for other procedures. Sugar did not affect pain-related

electrical activity This is a list of electrical phenomena. Electrical phenomena are a somewhat arbitrary division of electromagnetic phenomena. Some examples are: * Biefeld–Brown effect — Thought by the person who coined the name, Thomas Townsend Brown, to ...

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

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 and ...

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 pai ...

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-ce ...

can significantly affect pain intensity. About 35% of people report marked relief after receiving a saline injection they believed to be

. This

placebo A placebo ( ) is a substance or treatment which is designed to have no therapeutic value. Common placebos include inert tablets (like sugar pills), inert injections (like Saline (medicine), saline), sham surgery, and other procedures. In general ...

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 scientifi ...

, published in January 2009, concluded there was little difference in the effect of real, faked and no acupuncture. However, more recent reviews have found some benefit. Additionally, there is tentative evidence for a few herbal medicines. There has been some interest in the relationship between

vitamin D Vitamin D is a group of fat-soluble secosteroids responsible for increasing intestinal absorption of calcium, magnesium, and phosphate, and many other biological effects. In humans, the most important compounds in this group are vitamin D3 (c ...

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, dieta ...

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 bon ...

, is inconclusive. For chronic (long-term)

lower back pain Low back pain (LBP) or lumbago is a common 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 vary from a dull constant ache to a sudden sharp feeli ...

, spinal manipulation produces tiny, clinically insignificant, short-term improvements in pain and function, compared with sham therapy 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.

Epidemiology

Pain is the main reason for visiting an emergency department 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 determinants of health and disease conditions in a defined population. It is a cornerstone of public health, and shapes policy decisions and evidenc ...

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

 policy, drug control, 

animal rights Animal rights is the philosophy according to which many or all sentient animals have moral worth that is independent of their utility for humans, and that their most basic interests—such as avoiding suffering—should be afforded the sa ...

animal welfare Animal welfare is the well-being of non-human 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 such as longevity ...

torture Torture is the deliberate infliction of severe pain or suffering on a person for reasons such as punishment, extracting a confession, interrogation for information, or intimidating third parties. Some definitions are restricted to acts c ...

, and 

pain compliance Pain compliance is the use of painful stimulus to control or direct an organism. The stimulus can be manual (brute force, placing pressure on painful areas, or use of painful hyperextension or hyperflexion on joints), use tools such as a whip or ...

. The deliberate infliction of pain and the medical management of pain are both important aspects of

biopower Biopower (or ''biopouvoir'' in French) is a term coined by French scholar, philosopher, historian, and social theorist Michel Foucault. It relates to the practice of modern nation states and their regulation of their subjects through "an expl ...

, 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 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 "relationship between an individual and a state to which the individual owes allegiance and in turn is entitled to its protection". Each state determines the conditions under which it will recognize persons as its citizens, and ...

has been reserved for offences posing severe threat to the social fabric (for example,

treason Treason is the crime of attacking a state authority to which one owes allegiance. This typically includes acts such as participating in a war against one's native country, attempting to overthrow its government, spying on its military, its diplo ...

). 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 Catholic

self-flagellation Self-flagellation is the disciplinary and devotional practice of 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 of the flesh ...

practices, or personal

catharsis Catharsis (from Greek , , meaning "purification" or "cleansing" or "clarification") is the purification and purgation of emotions through dramatic art, or it may be any extreme emotional state that results in renewal and restoration. In its lite ...

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

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 land-grant research university in Fort Collins, Colorado. It is the flagship university of the Colorado State University System. Colorado State University is classified among "R1: ...

, 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.

Explanatory notes

References

External links

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"Pain"
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Stanford Encyclopedia of Philosophy The ''Stanford Encyclopedia of Philosophy'' (''SEP'') combines an online encyclopedia of philosophy with peer-reviewed publication of original papers in philosophy, freely accessible to Internet users. It is maintained by Stanford University. Eac ...

'' {{Authority control Acute pain Nociception Sensory systems Suffering Symptoms and signs