Medical expert of the article
New publications
Pain
Last reviewed: 04.07.2025
All iLive content is medically reviewed or fact checked to ensure as much factual accuracy as possible.
We have strict sourcing guidelines and only link to reputable media sites, academic research institutions and, whenever possible, medically peer reviewed studies. Note that the numbers in parentheses ([1], [2], etc.) are clickable links to these studies.
If you feel that any of our content is inaccurate, out-of-date, or otherwise questionable, please select it and press Ctrl + Enter.
Pain is an unpleasant sensation and emotional experience associated with actual or potential tissue damage or a condition described in terms of such damage.
The phenomenon of pain is not limited solely to organic or functional disorders at the site of its localization; pain also affects the functioning of the body as an individual. Over the years, researchers have described an innumerable number of adverse physiological and psychological consequences of unrelieved pain.
The physiological consequences of untreated pain of any localization can include everything from deterioration of the gastrointestinal tract and respiratory system to increased metabolic processes, increased tumor growth and metastases, decreased immunity and prolonged healing times, insomnia, increased blood clotting, loss of appetite, and decreased ability to work.
Psychological consequences of pain may manifest as anger, irritability, fear and anxiety, resentment, loss of spirit, despondency, depression, isolation, loss of interest in life, decreased ability to perform family duties, decreased sexual activity, which leads to family conflicts and even a request for euthanasia. Psychological and emotional effects often influence the patient's subjective reaction, exaggeration or underestimation of the significance of pain. In addition, a certain role in the severity of the psychological consequences of pain can be played by the degree of self-control of pain and illness by the patient, the degree of psychosocial isolation, the quality of social support and, finally, the patient's knowledge of the causes of pain and its consequences. The doctor almost always has to deal with developed manifestations of pain - emotions and pain behavior. This means that the effectiveness of diagnosis and treatment is determined not only by the ability to identify the etiopathogenetic mechanisms of the somatic condition manifested or accompanied by pain, but also by the ability to see behind these manifestations the problems of limiting the patient's usual life.
Causes of pain
A significant number of works, including monographs, are devoted to the study of the causes and pathogenesis of pain and pain syndromes. As a scientific phenomenon, pain has been studied for over a hundred years.
A distinction is made between physiological and pathological pain.
Physiological pain occurs at the moment of perception of sensations by pain receptors, it is characterized by a short duration and is directly dependent on the strength and duration of the damaging factor. The behavioral reaction in this case interrupts the connection with the source of damage.
Pathological pain can arise both in receptors and in nerve fibers; it is associated with long-term healing and is more destructive due to the potential threat of disruption of the normal psychological and social existence of the individual; the behavioral reaction in this case is the appearance of anxiety, depression, oppression, which aggravates somatic pathology. Examples of pathological pain: pain in the focus of inflammation, neuropathic pain, deafferentation pain, central pain. Each type of pathological pain has clinical features that allow us to recognize its causes, mechanisms and localization.
Types of pain
There are two types of pain.
The first type is acute pain caused by tissue damage that decreases as it heals. Acute pain has a sudden onset, is short-lived, clearly localized, and occurs when exposed to intense mechanical, thermal, or chemical factors. It can be caused by infection, injury, or surgery, lasts for hours or days, and is often accompanied by symptoms such as increased heart rate, sweating, pallor, and insomnia.
The second type - chronic pain develops as a result of damage or inflammation of tissue or nerve fiber, it persists or reoccurs for months or even years after healing, does not have a protective function and becomes the cause of suffering for the patient, it is not accompanied by symptoms characteristic of acute pain. Unbearable chronic pain has a negative impact on the psychological, social and spiritual life of a person.
Somatic pain occurs when the skin of the body is damaged or stimulated, as well as when deeper structures such as muscles, joints, and bones are damaged. Bone metastases and surgical interventions are common causes of somatic pain in patients suffering from tumors. Somatic pain is usually constant and fairly well-defined; it is described as throbbing, gnawing, etc.
Visceral pain is caused by stretching, compression, inflammation or other irritation of the internal organs. It is described as deep, squeezing, generalized and may radiate to the skin. Visceral pain is usually constant and difficult for the patient to localize.
Neuropathic (or deafferentation) pain occurs when nerves are damaged or irritated. It may be constant or intermittent, sometimes shooting, and is usually described as sharp, stabbing, cutting, burning, or unpleasant. Neuropathic pain is generally more severe than other types of pain and is more difficult to treat.
Clinically, pain can be classified as follows: nocigenic, neurogenic, psychogenic. This classification may be useful for initial therapy, but further such division is impossible due to the close combination of these pains.
Nocigenic pain occurs when skin nociceptors, deep tissue nociceptors, or internal organs are irritated. The resulting impulses follow classic anatomical pathways, reaching the higher parts of the nervous system, are reflected by consciousness, and form the sensation of pain. Pain from damage to internal organs is a consequence of rapid contraction, spasm, or stretching of smooth muscles, since smooth muscles themselves are insensitive to heat, cold, or dissection. Pain from internal organs with sympathetic innervation can be felt in certain areas on the body surface (Zakharyin-Ged zones) - this is referred pain. The most well-known examples of such pain are pain in the right shoulder and right side of the neck with gallbladder damage, pain in the lower back with bladder disease, and, finally, pain in the left arm and left half of the chest with heart disease. The neuroanatomical basis of this phenomenon is not entirely clear. A possible explanation is that the segmental innervation of the internal organs is the same as that of distant areas of the body surface, but this does not explain the reason for the reflection of pain from the organ to the body surface. The nocigenic type of pain is therapeutically sensitive to morphine and other narcotic analgesics.
Neurogenic pain. This type of pain can be defined as pain due to damage to the peripheral or central nervous system and is not explained by stimulation of nociceptors. Neurogenic pain has many clinical forms. These include some lesions of the peripheral nervous system, such as postherpetic neuralgia, diabetic neuropathy, incomplete damage to the peripheral nerve, especially the median and ulnar (reflex sympathetic dystrophy), and avulsion of the branches of the brachial plexus. Neurogenic pain due to damage to the central nervous system is usually due to cerebrovascular accident - this is known under the classical name of "thalamic syndrome", although studies (Bowsher et al., 1984) show that in most cases the lesions are located in areas other than the thalamus.
Psychogenic pain. The assertion that pain can be exclusively of psychogenic origin is debatable. It is widely known that the patient's personality shapes the sensation of pain. It is enhanced in hysterical personalities and more accurately reflects reality in patients of the non-hysterical type. It is known that people of different ethnic groups differ in their perception of postoperative pain. Patients of European descent report less intense pain than American blacks or Hispanics. They also report lower pain intensity compared to Asians, although these differences are not very significant (Faucett et al., 1994). Some people are more resistant to the development of neurogenic pain. Since this tendency has the above-mentioned ethnic and cultural features, it seems to be innate. Therefore, the prospects of research aimed at finding the localization and isolation of the "pain gene" are so tempting (Rappaport, 1996).
Neuropathic pain. Neuropathic (neurogenic) pain as a type of chronic pain is caused by damage to the peripheral or central nervous system, or by a disease affecting any sensory nerves or central ganglia. Examples: low back pain, diabetic neuropathy, postherpetic neuralgia, posttraumatic central or thalamic pain, and postamputation phantom pain.
Neuropathic pain is usually classified based on the etiologic factor causing damage to the nervous system or based on the anatomical localization of pain (trigeminal, glossopharyngeal, intercostal neuralgia). Neuropathic pain is characterized by a complex of negative and positive syndromes. Loss syndromes are manifested by sensory deficit in the form of complete or partial loss of sensitivity in the innervation zone of the affected nerves. Positive symptoms are characterized by the presence of spontaneous pain in combination with dysesthesia and paresthesia.
[