Phantom limb pain and phantom limb sensations are linked, but must be differentiated from one another. While phantom limb sensations are experienced by those with congenital limb deficiency, spinal cord injury, and amputation, phantom limb pain occurs almost exclusively as a result of amputation. Almost immediately following the amputation of a limb, 90-98% of patients report experiencing a phantom sensation. Nearly 75% of individuals experience the phantom as soon as anesthesia wears off, and the remaining 25% of patients experience phantoms within a few days or weeks. Of those experiencing innocuous sensations, a majority of patients also report distinct painful sensations.

Age and gender have not been shown to affect the onset or duration of phantom limb pain. Although it has not been fully explored, one investigation of lower limb amputation observed that as stump length decreased, there was a greater incidence of moderate and severe phantom pain.

Phantom pain involves the sensation of pain in a part of the body that has been removed.

Although not all phantom limbs are painful, people will sometimes feel as if they are gesturing, feel itches, twitch, or even try to pick things up. The missing limb often feels shorter and may feel as if it is in a distorted and painful position. Occasionally, the pain can be made worse by stress, anxiety, and weather changes. Phantom limb pain is usually intermittent. The frequency and intensity of attacks usually declines with time.

Some people who have undergone gender reassignment surgery have reported the sensation of phantom genitals. The reports were less common among post-operative transgender women, but did occur in transgender men. Similarly, subjects who had undergone mastectomy reported experiencing phantom breasts; these reports were substantially less common among post-operative transgender men, but did occur in transgender women.

CRPS can occur at any age with the average age at diagnosis being 42. It affects both men and women; however, CRPS is three times more frequent in females than males.

CRPS affects both adults and children, and the number of reported CRPS cases among adolescents and young adults has been increasing, with a recent observational study finding an incidence of 1.16/100,000 among children in Scotland.

A phantom limb is the sensation that an amputated or missing limb is still attached. Approximately 60 to 80% of individuals with an amputation experience phantom sensations in their amputated limb, and the majority of the sensations are painful. Phantom sensations may also occur after the removal of body parts other than the limbs, e.g. after amputation of the breast, extraction of a tooth (phantom tooth pain) or removal of an eye (phantom eye syndrome).

Good progress can be made in treating CRPS if treatment is begun early, ideally within three months of the first symptoms. If treatment is delayed, however, the disorder can quickly spread to the entire limb, and changes in bone, nerve, and muscle may become irreversible. The prognosis is not always good. Johns Hopkins Hospital reports that 77% of sufferers have spreads from the original site or flares in other parts of the body. The limb, or limbs, can experience muscle atrophy, loss of use, and functionally useless parameters that require amputation. RSD/CRPS will not "burn itself out", but if treated early, it is likely to go into remission. Once one is diagnosed with Complex Regional Pain Syndrome, the likelihood of it resurfacing after going into remission is significant. It is important to take precautions and seek immediate treatment upon any injury.

About 50% of women experience low back pain during pregnancy. Some studies have suggested women who have experienced back pain before pregnancy are at a higher risk of having back pain during pregnancy. It may be severe enough to cause significant pain and disability in up to a third of pregnant women. Back pain typically begins at around 18 weeks gestation, and peaks between 24 and 36 weeks gestation. Approximately 16% of women who experienced back pain during pregnancy report continued back pain years after pregnancy, indicating those with significant back pain are at greater risk of back pain following pregnancy.

Biomechanical factors of pregnancy shown to be associated with back pain include increased curvature of the lower back, or lumbar lordosis, to support the added weight on the abdomen. Also, a hormone called relaxin is released during pregnancy that softens the structural tissues in the pelvis and lower back to prepare for vaginal delivery. This softening and increased flexibility of the ligaments and joints in the lower back can result in pain. Back pain in pregnancy is often accompanied by radicular symptoms, suggested to be caused by the fetus pressing on the sacral plexus and lumbar plexus in the pelvis.

Typical factors aggravating the back pain of pregnancy include standing, sitting, forward bending, lifting, and walking. Back pain in pregnancy may also be characterized by pain radiating into the thigh and buttocks, night-time pain severe enough to wake the patient, pain that is increased during the night-time, or pain that is increased during the day-time.

Local heat, acetaminophen (paracetamol), and massage can be used to help relieve the pain. Avoiding standing for prolonged periods of time is also suggested.

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 (Na1.7) necessary in conducting pain nerve stimuli.

Dysesthesia (or dysaesthesia) comes from the Greek word "dys", meaning "not-normal" and "aesthesis", which means "sensation" (abnormal sensation). It is defined as an unpleasant, abnormal sense of touch. It often presents as pain but may also present as an inappropriate, but not discomforting, sensation. It is caused by lesions of the nervous system, peripheral or central, and it involves sensations, whether spontaneous or evoked, such as burning, wetness, itching, electric shock, and pins and needles. Dysesthesia can include sensations in any bodily tissue, including most often the mouth, scalp, skin, or legs.

It is sometimes described as feeling like acid under the skin. Burning dysesthesia might accurately reflect an acidotic state in the synapses and perineural space. Some ion channels will open to a low pH, and the acid sensing ion channel has been shown to open at body temperature, in a model of nerve injury pain. Inappropriate, spontaneous firing in pain receptors has also been implicated as a cause of dysesthesia.

Patients suffering from dysesthesia can become incapacitated with pain, despite no apparent damage to the skin or other tissue. Patients suffering from dysesthesia also often suffer from psychological disorders.

Although dysesthesia is similar to phantom limb syndrome, they should not be confused. In phantom limb, the sensation is present in an amputated or absent limb, while dysesthesia refers to discomfort or pain in a tissue that has not been removed or amputated. The dysesthetic tissue may also not be part of a limb, but part of the body, such as the abdomen. The majority of individuals with both phantom limb and dysesthesia experience painful sensations.

Phantom pain refers to dysesthetic feelings in individuals who are paralyzed or who were born without limbs. It is caused by the improper innervation of the missing limbs by the nerves that would normally innervate the limb. Dysesthesia is caused by damage to the nerves themselves, rather than by an innervation of absent tissue.

Dysesthesia should not be confused with anesthesia or hypoesthesia, which refer to a loss of sensation, or paresthesia which refers to a distorted sensation. Dysesthesia is distinct in that it can, but not necessarily, refer to spontaneous sensations in the absence of stimuli. In the case of an evoked dysesthetic sensation, such as by the touch of clothing, the sensation is characterized not simply by an exaggeration of the feeling, but rather by a completely inappropriate sensation such as burning.

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 and 14.

Overall, the outcome for acute low back pain is positive. Pain and disability usually improve a great deal in the first six weeks, with complete recovery reported by 40 to 90%. In those who still have symptoms after six weeks, improvement is generally slower with only small gains up to one year. At one year, pain and disability levels are low to minimal in most people. Distress, previous low back pain, and job satisfaction are predictors of long-term outcome after an episode of acute pain. Certain psychological problems such as depression, or unhappiness due to loss of employment may prolong the episode of low back pain. Following a first episode of back pain, recurrences occur in more than half of people.

For persistent low back pain, the short-term outcome is also positive, with improvement in the first six weeks but very little improvement after that. At one year, those with chronic low back pain usually continue to have moderate pain and disability. People at higher risk of long-term disability include those with poor coping skills or with fear of activity (2.5 times more likely to have poor outcomes at one year), those with a poor ability to cope with pain, functional impairments, poor general health, or a significant psychiatric or psychological component to the pain (Waddell's signs).

Electroanalgesia is a form of analgesia, or pain relief, that uses electricity to ease pain. Electrical devices can be internal or external, at the site of pain (local) or delocalized throughout the whole body. It works by interfering with the electric currents of pain signals, inhibiting them from reaching the brain and inducing a response; different from traditional analgesics, such as opiates which mimic natural endorphins and NSAIDS (non-steroidal anti-inflammatory drugs) that help relieve inflammation and stop pain at the source. Electroanalgesia has a lower addictive potential and poses less health threats to the general public, but can cause serious health problems, even death, in people with other electrical devices such as pacemakers or internal hearing aids, or with heart problems.

Low back pain that lasts at least one day and limits activity is a common complaint. Globally, about 40% of people have LBP at some point in their lives, with estimates as high as 80% of people in the developed world. Approximately 9 to 12% of people (632 million) have LBP at any given point in time, and nearly one quarter (23.2%) report having it at some point over any one-month period. Difficulty most often begins between 20 and 40 years of age. Low back pain is more common among people aged 4080years, with the overall number of individuals affected expected to increase as the population ages.

It is not clear whether men or women have higher rates of low back pain. A 2012 review reported a rate of 9.6% among males and 8.7% among females. Another 2012 review found a higher rate in females than males, which the reviewers felt was possibly due to greater rates of pains due to osteoporosis, menstruation, and pregnancy among women, or possibly because women were more willing to report pain than men. An estimated 70% of women experience back pain during pregnancy with the rate being higher the further along in pregnancy. Current smokers – and especially those who are adolescents – are more likely to have low back pain than former smokers, and former smokers are more likely to have low back pain than those who have never smoked.

Usually, acute pain is generated from an obvious cause and is expected to last for only a few days or weeks. It is usually managed with medication and non-pharmacological treatment to provide comfort. Acute pain is an indication for needed assessment, treatment and prevention. While a child is experiencing pain, physiological changes occur that can further jeopardize healing and recovery. Unrelieved pain can cause alkalosis and hypoxemia that result from rapid, shallow breathing. This shallow breathing then leads to the accumulation of fluid in the lungs, taking away to the ability to cough. Dangerously enough, this can prevent the secretions from being expelled. Pain can cause an increase in blood pressure and heart rate, creating great stress on the heart. Additionally, pain increases the release of anti-inflammatory steroids that reduce the ability to fight infection. These same steroids that are released increase the metabolic rate and impact healing. Another harmful outcome of acute pain is an increase in sympathetic effects such as the inability to urinate. Such aches can even slow down the gastrointestinal system.

Inadequate pain management in children can lead to psycho-social consequences. Disinterest in food, apathy, sleep problems, anxiety, avoidance of discussions about health, fear, hopelessness and powerlessness are just some of the many. Other consequences can be extended hospital stays, high readmission rates and a longer recovery. On the other hand, the American Association of Pediatrics describes pain with immunizations as "The pain associated with the majority of immunizations is minor.".

Examples of harmful consequences due to unrelieved pain:

- infants with a higher than average heel sticks can have poor cognitive and motor function

- distress caused by needle-sticks make medical treatments later on more difficult

- children who have experienced invasive procedures often times develop post-traumatic stress (PST)

- boys circumcised without anesthesia were found to have greater distress than uncircumcised boys.

- severe pain as a child is associated with higher reports of pain in adults

Acute pain can be expected in response to many if not most invasive procedures. Anticipation of pain and distress can guide a pre-treatment, pain-prevention plan based on past reports of pain associated with the medical procedure. Individuals with technical expertise and experience are more likely to minimize the pain as much as possible. Preparation before a procedure with information that is understood by children and parents decrease distress. Parents can contribute to the improvement of this issue by learning effective methods/ways to comfort their child. Types of procedures determine the use of deep sedation or anesthesia. In some cases, the best method to prevent and relieve pain is by building self-esteem. Suggested cognitive behavioral strategies are: imagery, relaxation, a massage, heat compression, calm adults, a quiet environment, and confident explanations by providers. Since distress can be addressed and controlled, some children benefit from the opportunity for self-regulation. Pain reduction during invasive procedures is closely linked to controlling distress. Treating distress even for minor or uncomplicated procedures, likes venipuncture can be implemented.

Neuropathic pain is associated with nerve injuries or abnormal sensitivities to touch or contact. Other causes are, postsurgical, post-amputation.

There is moderate quality evidence that suggests the combination of education and exercise may reduce an individual's risk of developing an episode of low back pain. Lesser quality evidence points to exercise alone as a possible deterrent to the risk of the onset of this condition.

Of the millions experiencing strokes worldwide, over 30,000 in the United States alone have developed some form of Dejerine–Roussy syndrome. 8% of all stroke patients will experience central pain syndrome, with 5% experiencing moderate to severe pain. The risk of developing Dejerine–Roussy syndrome is higher in older stroke patients, about 11% of stroke patients over the age of 80.

The cause of phantom vibrations is not known. Preliminary research suggests it is related to over-involvement with one's cell phone. Vibrations typically begin occurring after carrying a phone for between one month and one year. It has been suggested that, when anticipating a phone call, the cerebral cortex may misinterpret other sensory input (such as muscle contractions, pressure from clothing, or music) as a phone vibration or ring tone. This may be understood as a human signal detection issue, with potentially significant influences from psychological attributes. Factors such as experiences, expectations, and psychological states influence the threshold for signal detection. Some phantom vibration experiences may be a type of pareidolia and can therefore be examined as a psychological phenomenon influenced by individual variances in personality, condition, and context. Attachment anxiety can also be seen as a predictor for the frequency of phantom vibration experiences since it is associated with psychological attributes related to insecurity in interpersonal relationships.

A theoretical explanation for the mechanism of pain reduction by transcranial electrostimulation, or TCES, suggests that the electrical stimulation activates the anti-nociceptive system in the brain, resulting in β-endorphin, serotonin and noradrenaline release. TCES can be used on people with cervical pain, chronic lower back syndrome, or migraines. It cannot be used on people with orthopedic or radiological potentially serious spinal conditions, hydrocephalus, epilepsy, glaucoma, malignant hypertension, pacemaker or other implanted electronic device; recent cerebral trauma, nervous system infection, skin lesions at sites of electrode placement; oncological disease; patients undergoing any other treatments for pain; any invasive therapy, e.g. surgery, within the last month. The equipment used is Pulse Mazor Instruments' Pulsatilla 1000, which consists of a headset with three electrodes, two that go behind the ears and one that goes on the forehead, that release set frequencies of electricity at set intervals.

Hyperalgesia ( or ; 'hyper' from Greek ὑπέρ (huper, “over”), '-algesia' from Greek algos, ἄλγος (pain)) is an increased sensitivity to pain, which may be caused by damage to nociceptors or peripheral nerves. Prostaglandins E and F are largely responsible for sensitizing the nociceptors. Temporary increased sensitivity to pain also occurs as part of sickness behavior, the evolved response to infection.

ATN is usually attributed to inflammation or demyelination, with increased sensitivity of the trigeminal nerve. These effects are believed to be caused by infection, demyelinating diseases, or compression of the trigeminal nerve (by an impinging vein or artery, a tumor, or arteriovenous malformation) and are often confused with dental problems. An interesting aspect is that this form affects both men and women equally and can occur at any age, unlike typical trigeminal neuralgia, which is seen most commonly in women. Though TN and ATN most often present in the fifth decade, cases have been documented as early as infancy.

There is strong evidence to show that chronic orofacial pain (including AFP) is associated with psychological factors. Sometimes stressful life events appear to precede the onset of AFP, such as bereavement or illness in a family member. Hypochondriasis, especially cancerophobia, is also often cited as being involved. Most people with AFP are "normal" people who have been under extreme stress, however other persons with AFP have neuroses or personality disorders, and a small minority have psychoses. Some have been separated from their parents as children.

Depression, anxiety and altered behavior are strongly correlated with AFP. It is argued whether this is a sole or contributing cause of AFP, or the emotional consequences of suffering with chronic, unrelieved pain. It has been suggested that over 50% of people with AFP have concomitant depression or hypochondria. Furthermore, about 80% of persons with psychogenic facial pain report other chronic pain conditions such as listed in the table.

The trigeminal nerve is a mixed cranial nerve responsible for sensory data such as tactition (pressure), thermoception (temperature), and nociception (pain) originating from the face above the jawline; it is also responsible for the motor function of the muscles of mastication, the muscles involved in chewing but not facial expression.

Several theories exist to explain the possible causes of this pain syndrome. It was once believed that the nerve was compressed in the opening from the inside to the outside of the skull; but leading research indicates that it is an enlarged or lengthened blood vessel – most commonly the superior cerebellar artery – compressing or throbbing against the microvasculature of the trigeminal nerve near its connection with the pons. Such a compression can injure the nerve's protective myelin sheath and cause erratic and hyperactive functioning of the nerve. This can lead to pain attacks at the slightest stimulation of any area served by the nerve as well as hinder the nerve's ability to shut off the pain signals after the stimulation ends. This type of injury may rarely be caused by an aneurysm (an outpouching of a blood vessel); by an AVM (arteriovenous malformation); by a tumor; such as an arachnoid cyst or meningioma in the cerebellopontine angle; or by a traumatic event such as a car accident.

Short-term peripheral compression is often painless. Persistent compression results in local demyelination with no loss of axon potential continuity. Chronic nerve entrapment results in demyelination primarily, with progressive axonal degeneration subsequently. It is, "therefore widely accepted that trigeminal neuralgia is associated with demyelination of axons in the Gasserian ganglion, the dorsal root, or both." It has been suggested that this compression may be related to an aberrant branch of the superior cerebellar artery that lies on the trigeminal nerve. Further causes, besides an aneurysm, multiple sclerosis or cerebellopontine angle tumor, include: a posterior fossa tumor, any other expanding lesion or even brainstem diseases from strokes.

Trigeminal neuralgia is found in 3–4% of people with multiple sclerosis, according to data from seven studies. It has been theorized that this is due to damage to the spinal trigeminal complex. Trigeminal pain has a similar presentation in patients with and without MS.

Postherpetic neuralgia, which occurs after shingles, may cause similar symptoms if the trigeminal nerve is damaged.

When there is no [apparent] structural cause, the syndrome is called idiopathic.

In most studies, a majority of cell phone users report experiencing occasional phantom vibrations or ringing, with reported rates ranging from 27.4% to 89%. Once every two weeks is a typical frequency for the sensations, though a minority experience them daily. Most people are not seriously bothered by the sensations.