Pain is a distressing feeling often caused by intense or damaging
stimuli. The International Association for the Study of Pain's widely
used definition defines pain as "an unpleasant sensory and emotional
experience associated with actual or potential tissue damage, or
described in terms of such damage"; however, due to it being a
complex, subjective phenomenon, defining pain has been a challenge. In
medical diagnosis, pain is regarded as a symptom of an underlying
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 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 and
general functioning. Simple pain medications are useful in 20% to
70% of cases. Psychological factors such as social support,
hypnotic suggestion, excitement, or distraction can significantly
affect pain's intensity or unpleasantness. In some debates
regarding physician-assisted suicide or euthanasia, pain has been used
as an argument to permit people who are terminally ill to end their
1.5 Breakthrough pain
Pain asymbolia and insensitivity
2 Effect on functioning
3.1 Historical theories
3.2 Three dimensions of pain
3.3 Theory today
3.4 Evolutionary and behavioral role
4.1 Visual analogue scale
4.2 Multidimensional pain inventory
4.3 Assessment in people who are non-verbal
4.4 Other barriers to reporting
4.5 As an aid to diagnosis
4.6 Physiological measurement of pain
5.3 Alternative medicine
7 Society and culture
8 Other animals
10 See also
13 External links
In 1994, responding to the need for a more useful system for
describing chronic pain, the International Association for the Study
Pain (IASP) classified pain according to specific characteristics:
region of the body involved (e.g. abdomen, lower limbs),
system whose dysfunction may be causing the pain (e.g., nervous,
duration and pattern of occurrence,
intensity and time since onset, and
However, this system has been criticized by
Clifford J. Woolf and
others as inadequate for guiding research and treatment. Woolf
suggests three classes of pain:
inflammatory pain which is associated with tissue damage and the
infiltration of immune cells, and
pathological pain which is a disease state caused by damage to the
nervous system or by its abnormal function (e.g. fibromyalgia,
peripheral neuropathy, tension type headache, etc.).
Main article: Chronic pain
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, peripheral
neuropathy, cancer and idiopathic 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 from onset; 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.:93 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 durations,
is "pain that extends beyond the expected period of healing".
Chronic pain may be classified as cancer pain or else as benign.
Main article: Nociception
Mechanism of nociceptive pain.
Nociceptive pain is caused by stimulation of sensory nerve fibers that
respond to stimuli approaching or exceeding harmful intensity
(nociceptors), 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 in a cut or chemicals released during
inflammation). Some nociceptors respond to more than one of these
modalities and are consequently designated polymodal.
Nociceptive pain may also be divided into "visceral", "deep somatic"
and "superficial somatic" pain. Visceral structures are highly
sensitive to stretch, ischemia and inflammation, but relatively
insensitive to other stimuli that normally evoke pain in other
structures, such as burning and cutting.
Visceral pain 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, fasciae and muscles, and is dull,
aching, poorly-localized pain. Examples include sprains and broken
bones. Superficial 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.
Main article: Neuropathic pain
Neuropathic pain is caused by damage or disease affecting any part of
the nervous system involved in bodily feelings (the somatosensory
system). Peripheral neuropathic pain is often described as
"burning", "tingling", "electrical", "stabbing", or "pins and
needles". Bumping the "funny bone" elicits acute peripheral
Allodynia is pain experienced in response to a normally painless
stimuli. It has no biological function and is classified by
stimuli into dynamic mechanical, punctate and static. In
osteoarthritis, NGF has been identified as being involved in
allodynia. The extent and intensity of sensation can be assessed
through locating trigger points and the region of sensation, as well
as utilising phantom maps.
Main article: Phantom pain
Phantom pain is pain felt in a part of the body that has been
amputated, or from which the brain no longer receives signals. It is a
type of neuropathic pain.
The prevalence 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 or
Local anesthetic 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 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
Mirror box therapy produces the illusion of movement and touch in a
phantom limb which in turn may cause a reduction in pain.
Paraplegia, 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 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.:61–9
Main article: Psychogenic pain
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. Sufferers 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
People with long-term pain frequently display psychological
disturbance, with elevated scores on the Minnesota Multiphasic
Personality Inventory scales of hysteria, depression and
hypochondriasis (the "neurotic triad"). 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. When long-term pain is relieved by therapeutic
intervention, scores on the neurotic triad and anxiety fall, often to
normal levels. Self-esteem, often low in chronic pain patients, also
shows improvement once pain has resolved.:31–2
Breakthrough pain is transitory acute pain that comes on suddenly and
is not alleviated by the patient's regular pain management. 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 vary from person to person and according to the cause. Management
of breakthrough pain can entail intensive use of opioids, including
Pain asymbolia and insensitivity
Pain asymbolia and Congenital insensitivity to pain
"Painless" redirects here. For other uses, see Painless
A patient and doctor discuss congenital insensitivity to pain
The ability to experience pain is essential for protection from
injury, and recognition of the presence of injury. Episodic analgesia
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, it is possible to induce a state described as intense pain
devoid of unpleasantness in some patients, with morphine 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. This is usually the result of acquired damage to the
nerves, such as spinal cord injury, diabetes mellitus (diabetic
neuropathy), or leprosy 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". 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 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. A very rare
syndrome with isolated congenital insensitivity to pain has been
linked with mutations in the
SCN9A gene, which codes for a sodium
channel (Nav1.7) necessary in conducting pain nerve stimuli.
Effect on functioning
Experimental subjects challenged by acute pain and patients in chronic
pain experience impairments in attention control, working memory,
mental flexibility, problem solving, and information processing
speed. Acute and chronic pain are also associated with increased
depression, anxiety, fear, and anger.
If I have matters right, the consequences of pain will include direct
physical distress, unemployment, financial difficulties, marital
disharmony, and difficulties in concentration and attention…
— Harold Merskey 2000
See also: History of pain theory
Before the relatively recent discovery of neurons 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
Hippocrates believed that it was due to an imbalance
in vital fluids. In the 11th century,
Avicenna theorized that
there were a number of feeling senses including touch, pain and
René Descartes by Jan Baptist Weenix, 1647-1649
René Descartes theorized that pain was a disturbance that
passed down 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 and experiments by Max
von Frey, 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.
In 1955, DC Sinclair and G Weddell developed peripheral pattern
theory, based on a 1934 suggestion by John Paul Nafe. They proposed
that all skin fiber endings (with the exception of those innervating
hair cells) are identical, and that pain is produced by intense
stimulation of these fibers. Another 20th-century theory was gate
control theory, introduced by
Ronald Melzack and Patrick Wall in the
1965 Science article "
Pain Mechanisms: A New Theory". The authors
proposed that both thin (pain) and large diameter (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 the
more large fiber activity relative to thin fiber activity at the
inhibitory cell, the less pain is felt.
Three dimensions of pain
Ronald Melzack and Kenneth Casey described 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
"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 dimensions of pain, while suggestion and
placebos may modulate 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)
Regions of the cerebral cortex associated with pain.
Wilhelm Erb's (1874) "intensive" theory, that a pain signal can be
generated by intense enough stimulation of any sensory receptor, has
been soundly disproved. Some sensory fibers do not differentiate
between noxious and non-noxious stimuli, while others, nociceptors,
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 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 channels 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 an
A-delta or C fiber. Because the A-delta fiber is thicker than the C
fiber, and is thinly sheathed in an electrically insulating material
(myelin), it carries its signal faster (5–30 m/s) than the
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 "first order" neurons enter the spinal cord via
These A-delta and C fibers connect with "second order" nerve fibers in
the central gelatinous substance of the spinal cord (laminae II and
III of the dorsal horns). The second order fibers then cross the cord
via the anterior white commissure and ascend in the spinothalamic
tract. Before reaching the brain, the spinothalamic tract splits into
the lateral, neospinothalamic tract and the medial, paleospinothalamic
Second order, 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 have been identified. Other spinal cord
fibers, known as wide dynamic range neurons, respond to A-delta and C
fibers, but also to the large A-beta fibers that carry touch, pressure
and vibration signals. Pain-related activity in the thalamus
spreads to the insular cortex (thought to embody, among other things,
the feeling that distinguishes pain from other homeostatic emotions
such as itch and nausea) and anterior cingulate cortex (thought to
embody, among other things, the affective/motivational element, the
unpleasantness of pain).
Pain that is distinctly located also
activates primary and secondary somatosensory cortex.
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 have reduced life expectancy.
In The Greatest Show on Earth: The Evidence for Evolution, biologist
Richard Dawkins 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.[a] This resemblance will not be perfect, however,
because natural selection can be a poor designer. This may have
maladaptive results such as supernormal stimuli.
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 psychologists argue that such pain is psychogenic,
enlisted as a protective distraction to keep dangerous emotions
In pain science, thresholds are measured by gradually increasing the
intensity of a stimulus such as electric current or heat applied to
the body. The pain perception threshold is the point at which the
stimulus begins to hurt, and the pain tolerance threshold is reached
when the subject acts to stop the pain.
Differences in pain perception and tolerance thresholds are associated
with, among other factors, ethnicity, genetics, and sex. People of
Mediterranean origin report as painful some radiant heat intensities
that northern Europeans describe as nonpainful. And Italian women
tolerate less intense electric shock than Jewish or Native American
women. Some individuals in all cultures have significantly higher than
normal pain perception and tolerance thresholds. For instance,
patients who experience painless heart attacks have higher pain
thresholds for electric shock, muscle cramp and heat.:17–9
Pain scales, and
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: "
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 indicating which words best describe their pain.
Visual analogue scale
Main article: 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
Pain Inventory (MPI) is a questionnaire designed
to assess the psychosocial state of a person with chronic pain.
Analysis of MPI results by Turk and Rudy (1988) found three classes of
chronic pain patient: "(a) dysfunctional, people who perceived the
severity of their pain to be high, reported that pain interfered with
much of their lives, reported a higher degree of psychological
distress caused by pain, and reported low levels of activity; (b)
interpersonally distressed, people with a common perception that
significant others were not very supportive of their pain problems;
and (c) adaptive copers, patients who reported high levels of social
support, relatively low levels of pain and perceived interference, and
relatively high levels of activity." Combining the MPI
characterization of the person with their IASP five-category pain
profile is recommended for deriving the most useful case
Assessment in people who are non-verbal
Pain and dementia
Pain and dementia and
Pain in babies
When a person is non-verbal and cannot self-report pain, observation
becomes critical, and specific behaviors can be monitored as pain
indicators. Behaviors such as facial grimacing and guarding 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 and possibly
experience a decreased appetite 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
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.
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
Other barriers to reporting
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. Depression may also keep
older adult from reporting they are in pain. Decline in self-care may
also indicate the older adult is experiencing pain. They be reluctant
to report pain because they 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.
Sufferers may feel certain treatments 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 factor in reporting
pain. Sexual differences can be the result of social and cultural
expectations, with women expected to be more emotional and show pain,
and men more stoic.
As an aid to diagnosis
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, while chest
pain described as tearing may indicate aortic dissection.
Physiological measurement of pain
Functional magnetic resonance imaging
Functional magnetic resonance imaging brain scanning has been used to
measure pain, and correlates well with self-reported pain.
Pain management in children and
Inadequate treatment of pain is widespread throughout surgical wards,
intensive care units, and accident and emergency departments In
general practice, 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.
African and Hispanic Americans 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.
International Association for the Study of Pain advocates that the
relief of pain should be recognized as a human right, that chronic
pain should be considered a disease in its own right, and that pain
medicine should have the full status of a medical specialty. It is
a specialty only in China and Australia at this time. Elsewhere,
pain medicine is a subspecialty under disciplines such as
anesthesiology, physiatry, neurology, palliative medicine and
psychiatry. In 2011,
Human Rights Watch
Human Rights Watch alerted that tens of
millions of people worldwide are still denied access to inexpensive
medications for severe pain.
Breastfeeding may decrease pain when babies are immunized.
Acute pain is usually managed with medications such as analgesics and
Caffeine when added to pain medications such as
ibuprofen, may provide some additional benefit. Management of
chronic pain, however, is more difficult, and may require the
coordinated efforts of a pain management team, which typically
includes medical practitioners, clinical pharmacists, clinical
psychologists, physiotherapists, occupational therapists, physician
assistants, and nurse practitioners.
A seven-month-old, receiving a vaccine for polio
Sugar (sucrose) when taken by mouth reduces pain in newborn babies
undergoing some medical procedures (a lancing of the heel,
venipuncture, and intramuscular injections). Sugar does not remove
pain from circumcision, and it is unknown if sugar reduces pain for
other procedures. Sugar did not affect pain-related electrical
activity 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.
Individuals with more social support experience less cancer pain, take
less pain medication, report less labor pain and are less likely to
use epidural anesthesia during childbirth, or suffer from chest pain
after coronary artery bypass surgery.
Suggestion can significantly affect pain intensity. About 35% of
people report marked relief after receiving a saline injection they
believed to be morphine. This placebo 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.:26–8 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.:22–3
Cognitive behavioral therapy
Cognitive behavioral therapy (CBT) has been shown effective for
improving quality of life in those with chronic pain but the reduction
in suffering is modest, and the CBT method was not shown to have any
effect on outcome.
Acceptance and Commitment Therapy (ACT) may
also effective in the treatment of chronic pain.
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
Pain is the most common reason for people to use complementary and
alternative medicine. An analysis of the 13 highest quality
studies of pain treatment with acupuncture, published in January 2009,
concluded there was little difference in the effect of real, faked and
no acupuncture. However, other 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 and pain, but the evidence so far from
controlled trials for such a relationship, other than in osteomalacia,
A 2003 meta-analysis of randomized clinical trials found that spinal
manipulation was "more effective than sham therapy but was no more or
less effective than general practitioner care, analgesics, physical
therapy, exercise, or back school" in the treatment of lower back
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 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
Society and culture
The okipa ceremony as witnessed by George Catlin, circa 1835.
The nature or meaning of physical pain has been diversely understood
by religious or secular traditions from antiquity to modern
Physical pain is an important political topic in relation to various
issues, including pain management policy, drug control, animal rights
or animal welfare, torture, and pain compliance. In various contexts,
the deliberate infliction of pain in the form of corporal punishment
is used as retribution for an offence, or for the purpose of
disciplining or reforming a wrongdoer, or to deter attitudes or
behaviour deemed unacceptable. The slow slicing, or death by a
thousand cuts, was a form of execution in China reserved for crimes
viewed as especially severe, such as high treason or patricide. In
some cultures, extreme practices such as mortification of the flesh or
painful rites of passage are highly regarded. For example, the
Mawé people of Brazil use intentional bullet ant stings as
part of their initiation rites to become warriors.
Pain in animals
Pain in animals and
Pain in invertebrates
The most reliable method for assessing pain in most humans is by
asking a question: a person may report pain that cannot be detected by
any known physiological measure. However, like infants, animals cannot
answer questions about whether they feel pain; thus the defining
criterion for pain in humans cannot be applied to them. Philosophers
and scientists have responded to this difficulty in a variety of ways.
René Descartes for example argued that animals lack consciousness and
therefore do not experience pain and suffering in the way that humans
Bernard Rollin of Colorado State University, the principal
author of two U.S. federal laws regulating pain relief for animals,[b]
writes 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. In his
interactions with scientists and other veterinarians, he was regularly
asked to "prove" that animals are conscious, and to provide
"scientifically acceptable" grounds for claiming that they feel
pain. Carbone writes that the view that animals feel pain
differently is now a minority view. Academic reviews
of the topic are more equivocal, noting that although the argument
that animals have at least simple conscious thoughts and feelings has
strong support, some critics continue to question how reliably
animal mental states can be determined. The ability of
invertebrate species of animals, such as insects, to feel pain and
suffering is also unclear.
The presence of pain in an animal cannot be known for certain, but it
can be inferred through physical and behavioral reactions.
Specialists currently believe that all vertebrates can feel pain, and
that certain invertebrates, like the octopus, may also.
As for other animals, plants, or other entities, their ability to feel
physical pain is at present a question beyond scientific reach, since
no mechanism is known by which they could have such a feeling. In
particular, there are no known nociceptors in groups such as plants,
fungi, and most insects, except for instance in fruit flies.
In vertebrates, endogenous opioids are neuromodulators that moderate
pain by interacting with opioid receptors. Opioids and opioid
receptors occur naturally in crustaceans and, although at present no
certain conclusion can be drawn, their presence indicates that
lobsters may be able to experience pain. Opioids may mediate
their pain in the same way as in vertebrates. Veterinary medicine
uses, for actual or potential animal pain, the same analgesics and
anesthetics as used in humans.
First attested in English in 1297, the word peyn comes from the Old
French peine, in turn from
Latin poena meaning "punishment,
penalty" (in L.L. also meaning "torment, hardship, suffering")
and that from Greek ποινή (poine), generally meaning "price paid,
Hedonic adaptation, the tendency to quickly return to a relatively
stable level of happiness despite major positive or negative events
Pain and suffering, the legal term for the physical and emotional
stress caused from an injury
Pain (philosophy), the branch of Philosophy concerned with suffering
and physical pain
^ For example, lack of food, extreme cold, or serious injuries are
felt as exceptionally painful, whereas minor damage is felt as mere
^ Rollin drafted the 1985 Health Research Extension Act and an animal
welfare amendment to the 1985 Food Security Act.
^ a b "International Association for the Study of Pain: Pain
Definitions". Retrieved 12 January 2015.
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III familial dysautonomia
IV congenital insensitivity to pain with anhidrosis
V congenital insensitivity to pain with partial anhidrosis
Paroxysmal extreme pain disorder
Low back pain
Low back pain (LBP)
Cold pressor test
Grimace scale (animals)
Hot plate test
Tail flick test
Philosophy of pain
Merkel nerve ending
Free nerve ending
Intrafusal muscle fiber
Nuclear chain fiber
Nuclear bag fiber
The sensory system
Taste (Gustatory system)
Touch and position
Sense of balance
Sense of body parts and movement