Pain is an unpleasant sensory and emotional experience that signals actual or possible injury.
Understanding of pain has evolved over time to include several key concepts:
The concept of pain is learned through experiences.
A person's experience of pain is influenced by biomedical realities, psychological issues, and the social context in which that pain is experienced.
The experience of pain is always influenced by the personal feelings, perceptions, and/or opinions of the person affected.
Pain is the most common reason people seek medical care, and chronic pain, which is pain that lasts more than 3 months, impacts a large portion of the population. In 2023, the Centers for Disease Control and Prevention estimated that over 25% of adults in the United States had chronic pain and nearly 7% had high-impact chronic pain, meaning their chronic pain significantly restricted their ability to engage in daily activities. There are higher incidences of chronic pain in females and older adults. The most common locations for that pain are in the legs and feet, followed by the back, the arms and hands, and the head.
Pain may be sharp or dull, intermittent or constant, or throbbing or steady. Sometimes pain is very difficult to describe. Pain may be felt at a single site or over a large area. The intensity of pain can vary from mild to intolerable.
People differ remarkably in their ability to tolerate pain. One person has difficulty tolerating the pain of a small cut or bruise, but another person can tolerate pain caused by a major accident or knife wound. The ability to withstand pain varies according to mood, personality, and circumstance. In a moment of excitement during an athletic match, an athlete may not notice a severe bruise but is likely to be very aware of the pain after the match, particularly if the team lost.
A doctor should always respect a person's reported pain but keep in mind that not everyone can adequately communicate pain-related feelings and concerns. This inability does not indicate a lack of pain. Doctors will, therefore, watch for and follow up on nonverbal signs of pain during the evaluation (for example, sensitivity to touch or favoring one limb over another).
Spotlight on Aging: Pain
Conditions that cause pain are common among older adults. However, as people age, they complain less of pain. The reason may be a decrease in the body’s sensitivity to pain or a more stoical attitude toward pain. Some older adults mistakenly think that pain is an unavoidable part of aging and thus minimize it or do not report it. The most common cause of pain is a musculoskeletal disorder. However, many older adults have chronic pain, which may have many causes. Effects of pain may be more serious for older adults:
Older Adults and Pain Relievers Older adults are more likely than younger people to have side effects from pain relievers (analgesics), and some side effects are more likely to be severe. Analgesics may stay in the body longer, and older people may be more sensitive to them. Many older adults take several medications, increasing the chances that a medication will interact with the analgesic. Such interactions may reduce the effectiveness of one of the medications or increase the risk of side effects. Older adults are more likely to have health problems that increase the risk of side effects from analgesics. Nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen or naproxen, can have side effects. Risk of several side effects is higher in older adults, particularly if they have several other disorders or are taking NSAIDs in high doses. For example, older adults are more likely to have a heart or blood vessel (cardiovascular) disorder or risk factors for cardiovascular disorders. For people with these disorders or risk factors for them, taking NSAIDs increases their risk of having a heart attack or stroke and of developing blood clots in the legs or heart failure., such as ibuprofen or naproxen, can have side effects. Risk of several side effects is higher in older adults, particularly if they have several other disorders or are taking NSAIDs in high doses. For example, older adults are more likely to have a heart or blood vessel (cardiovascular) disorder or risk factors for cardiovascular disorders. For people with these disorders or risk factors for them, taking NSAIDs increases their risk of having a heart attack or stroke and of developing blood clots in the legs or heart failure. NSAIDs can damage the kidneys. This risk is higher for older people because the kidneys tend to function less well as people age. This risk of kidney damage is also higher in people with a kidney disorder, heart failure, or a liver disorder, which are more common among older adults. Older people are more likely to develop ulcers or bleeding in the digestive tract when they take NSAIDs. Doctors may prescribe a medication that helps protect the digestive tract from such damage. These medications include proton pump inhibitors (such as omeprazole) and misoprostol.(such as omeprazole) and misoprostol. When older adults take NSAIDs, they should tell their doctor, who then evaluates them periodically for side effects. Doctors also recommend the following for older adults if possible:
Opioids are more likely to cause problems in older adults, who appear to be more sensitive to these medications than younger people. When some older adults take an opioid for a short time, it reduces pain and enables them to function better physically, but it may impair mental functioning, sometimes causing confusion. Opioids also increase the risk of falls, and taking opioids for a long time can increase the risk of osteoporosis and fractures. Opioids cause constipation and urinary retention, which tend to cause more problems in older adults. Older adults are more likely to have conditions or take medications that can make them more likely to have side effects from opioids, such as the following:
Opioids may also cause dependence and addiction. Doctors usually treat pain with analgesics less likely to have side effects in older adults. For example, acetaminophenacetaminophen is usually preferred to NSAIDs for treating chronic mild to moderate pain without inflammation. Certain NSAIDs (indomethacin and ketorolac) and certain opioids (such as pentazocine) are usually not given to older adults because of the risk of side effects. If opioids are necessary, doctors give older adults a low dose at first. The dose is increased slowly as needed, and its effects are monitored. Buprenorphine may be a good choice, especially for older adults with a kidney disorder, because it may have a lower risk of side effects than other opioids.is usually preferred to NSAIDs for treating chronic mild to moderate pain without inflammation. Certain NSAIDs (indomethacin and ketorolac) and certain opioids (such as pentazocine) are usually not given to older adults because of the risk of side effects. If opioids are necessary, doctors give older adults a low dose at first. The dose is increased slowly as needed, and its effects are monitored. Buprenorphine may be a good choice, especially for older adults with a kidney disorder, because it may have a lower risk of side effects than other opioids. Nonmedication-related treatments and support from caregivers and family members can sometimes help older adults manage pain and reduce the need for analgesics. |
Pain pathways
Pain due to injury begins at special pain receptors scattered throughout the body. These pain receptors transmit signals as electrical impulses along nerves to the spinal cord and then upward to the brain. Sometimes the signal evokes a reflex response (see figure Reflex Arc: A No-Brainer). When the signal reaches the spinal cord, a signal is immediately sent back along motor nerves to the original site of the pain, triggering the muscles to contract without involving the brain. For example, when people inadvertently touch something very hot, they immediately pull away. This reflex reaction helps prevent permanent damage. The pain signal is also sent to the brain. Only when the brain processes the signal and interprets it as pain do people become aware of the pain.
Pain receptors and their nerve pathways differ in different parts of the body. For this reason, pain sensation varies with the type and location of injury. For example, pain receptors in the skin are plentiful and capable of transmitting precise information, including where an injury is located and whether the source was sharp, such as a knife wound, or dull, such as pressure, heat, cold, or itching. In contrast, pain receptors in internal organs, such as the intestine are limited and imprecise. The intestine can be pinched, cut, or burned without generating a pain signal. However, stretching and pressure can cause severe intestinal pain, even from something as relatively harmless as a trapped gas bubble. The brain cannot identify the precise source of intestinal pain, which is difficult to locate and is likely to be felt over a large area.
Reflex Arc: A No-Brainer
A reflex arc is the pathway that a nerve reflex, such as the knee jerk reflex, follows.
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Sometimes pain felt in one area of the body does not accurately represent where the problem is because the pain is referred there from another area. Pain can be referred because signals from several areas of the body often travel through the same nerve pathways in the spinal cord and brain. For example, pain from a heart attack may be felt in the neck, jaws, arms, or abdomen. Pain from a gallbladder attack may be felt in the back of the shoulder.
What Is Referred Pain?
Pain felt in one area of the body does not always represent where the problem is because the pain may be referred there from another area. For example, pain produced by a heart attack may feel as if it is coming from the arm because sensory information from the heart and the arm converge on the same nerve pathways in the spinal cord. |
Acute versus chronic pain
Pain may be acute or chronic. Acute pain means pain that begins suddenly and does not last long (days or weeks). Chronic pain lasts for many months or years.
When severe, acute pain may cause anxiety, a rapid heart rate, an increased breathing rate, elevated blood pressure, sweating, and dilated pupils. Usually, chronic pain does not have these effects, but it may result in other problems, such as depression, disturbed sleep, decreased energy, a poor appetite, weight loss, decreased sex drive, and loss of interest in activities.
Causes of Pain
Different types of pain have different causes.
Nociceptive pain results from stimulation of pain receptors. It is caused by an injury to body tissues. Most pain, particularly acute pain, is nociceptive pain.
Neuropathic pain results from damage to or dysfunction of the brain or spinal cord (central nervous system) or the nerves outside the brain and spinal cord (peripheral nervous system). It may occur when
Pressure is put on a specific nerve—for example, by a tumor or a ruptured disk in the spine, causing low back pain and/or pain radiating down the leg. Pressure on a nerve in the wrist can cause carpal tunnel syndrome.
Nerves are damaged, as occurs in diabetes mellitus or postherpetic neuralgia (pain after shingles).
The brain and spinal cord do not process pain signals normally or something disrupts this processing, as occurs in phantom limb pain and complex regional pain syndrome.
In diabetes, nerves outside the brain and spinal cord (peripheral nerves) are damaged. Symptoms include numbness, tingling, and pain in the toes, feet, and sometimes hands.
In postherpetic neuralgia, the area where the rash first occurred becomes painful and tender to the touch.
Nociceptive or neuropathic pain or both may be involved in acute or chronic pain. For example, chronic low back pain and most cancer pain are caused mainly by ongoing stimulation of pain receptors (nociceptive pain). But in these disorders, pain can also result from nerve damage (neuropathic pain).
Nociplastic pain, a more recently described third category of pain, is still poorly understood. It is thought to be caused by changes in the way pain signals are processed. Nociplastic pain tends to be more widespread throughout the body, that is to say, it is not as confined to specific areas as neuropathic and nociceptive pain. Nociplastic pain may also be associated with fatigue, gastrointestinal symptoms, sleep disturbances, and cognitive dysfunction. Fibromyalgia is an example of nociplastic pain, as are temporomandibular disorder and long COVID syndrome.
Psychological factors, such as depression, can also contribute to pain. Psychological factors often affect how people feel pain and how intense it seems, but these factors are rarely the only cause of pain.
