Pain is defined as an unpleasant sensory and emotional experience associated with damage to body tissues, including organs, bones, and muscles.
Pain is the most common reason individuals seek medical care. Pain is often classified as acute (immediate, short-term) or chronic (long-term).
Approximately 30-40 million Americans annually do not experience symptom relief with use of over-the-counter (OTC) analgesics, such as acetaminophen (Tylenol®), aspirin, and ibuprofen (Advil®). Some researchers estimate that 35% of Americans experience chronic pain.
According to the National Institutes of Health (NIH), the annual cost of chronic pain in the United States, including healthcare expenses, lost income, and lost productivity, is estimated to be about $100 billion.
The four most common types of pain are lower back pain, severe headache or migraine pain, neck pain, and facial ache or pain. Back pain is the leading cause of disability in Americans under 45 years old.
There is no objective measurement of pain for individuals. Pain can only be reported by the individual experiencing it.

Related Terms

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types of pain

Pain can either be acute (immediate and short-term) or chronic (long-term, lasting more then three months). Various pains are treated differently, based on severity and type. Pain can also be divided into categories that help explain its origin in the body and its effects on the body. The types of pain include nerve or neuropathic, nociceptive, or psychogenic.
Acute pain: Acute pain is a normal sensation in the nervous system to alert the individual to possible injury. Acute pain is triggered by a stimulus, such as getting cut by a knife, getting burned, or falling on a rock. Acute pain is frequently associated with anxiety, tachycardia (fast heart rate), increased respiratory rate, increased blood pressure, diaphoresis (sweating), and dilated pupils. Acute pain, for the most part, results from injury to tissues and/or inflammation. Acute pain generally has a sudden onset. For example, after trauma or surgery, acute pain may be accompanied by anxiety or emotional distress.
Chronic pain: Chronic pain is resistant to most medical treatments. Chronic pain can, and often does, cause severe problems for the individual. Pain signals keep firing in the nervous system for weeks, months, even years. Initial injuries, such as an infection, sprained back, or sprained muscle, may cause acute pain that may lead to chronic pain. There may be an ongoing cause of pain, such as in back pain, arthritis, diabetes (diabetic neuropathy), or cancer. Some individuals suffer chronic pain in the absence of any past injury or evidence of body damage. Many chronic pain conditions affect older adults.
Common chronic pain complaints include headache, lower back pain, cancer pain, arthritis pain, neuropathic pain (pain resulting from damage to the peripheral nerves or to the central nervous system itself), and psychogenic pain (pain not due to past disease or injury or any visible sign of damage inside or outside the nervous system).
Chronic pain may be associated with vegetative signs, such as fatigue (extreme tiredness), loss of libido (sexual drive), loss of appetite, and depressed mood. Individuals vary considerably in their tolerance for pain. Chronic pain is widely believed to represent disease itself. It can be made much worse by environmental and psychological factors.
Nerve pain: Nerve pain, or neuropathic pain, is caused by pressure or damage to nerves or the spinal cord. Nerve pain can be caused by: tumors; injury, such as during surgery or falls; chemical damage, such as with mercury, lead, chemotherapy, and radiation; or viruses, such as herpes zoster (shingles or chicken pox).
Nerve pain is severe and usually described as burning or tingling. Nerve pain usually occurs in one particular place on the body or along the path of a nerve. Nerve pain can occur in entire limbs, such as the legs or arms. Nerve pain has very different medication treatment options from other types of pain. For example, opioids (such as morphine) and non-steroidal anti-inflammatory drugs, or NSAIDs (such as ibuprofen, COX-2 inhibitors), are usually ineffective in relieving nerve pain.
Phantom pain is a type of nerve pain felt where an amputated limb used to be. The individual feels the presence of a missing limb through pain and sensation. Some secondary sources report that 60-70% of people who have had an arm or leg removed feel phantom limb pain. The pain may resemble squeezing, burning, or crushing sensations, but it often differs from any sensation previously experienced. For some people, phantom limb pain occurs less frequently as time passes, but for others, it persists. Massage can sometimes help, but drug therapy is sometimes necessary.
Nociceptive pain: Most pain is nociceptive pain. This type of pain is typically aching, sharp, or throbbing. Pain receptors for tissue injury (nocioreceptors) are located mostly in the skin or in the internal organs. These nocioreceptors are nerve fibers in the body that only send signals to the brain when they receive strong stimulation, such as with pain. Damage to these nocioreceptor neurons alters the way that they can respond to neurochemicals and makes them more sensitive after injury, which may be the cause of some types of chronic pain. Damage also causes the cells to release chemical mediators of pain and inflammation, including potassium ions, bradykinin, prostaglandins, serotonin, histamine, and substance P. Nociceptive pain is caused by an injury to body tissues. The injury may be a cut, bruise, bone fracture, crush injury, tumor invasion, burn, or anything that damages tissues. The pain experienced after surgery is almost always nociceptive pain. The pain may be constant or intermittent, often worsening when an individual moves, coughs, laughs, or breathes deeply or when the dressings over the surgical wound are changed. Nociceptive pain can be further divided into somatic pain and visceral pain.
Somatic pain is pain caused by activation of pain receptors in cutaneous (body surface) or deep tissues, such as muscle and bone. Common causes of somatic pain include minor problems such as paper cuts, burns, or scrapes. Severe somatic pain can occur with metastasis (spreading) of cancer into the bone, and post-surgical pain from a surgical incision, such as after cardiopulmonary bypass. Somatic pain is generally localized in one area of the body and is intense, sharp, and easily identifiable as compared to throbbing visceral pain.
The viscera refers to the internal areas of the body that are enclosed within a cavity. Visceral pain is caused by activation of pain receptors in the thoracic (chest), abdominal, or pelvic viscera. Common causes of visceral pain include pancreatic cancer, kidney disease, and metastases in the abdomen. Visceral pain is not well localized and is usually described as pressure-like, deep squeezing.
Psychogenic pain: Psychogenic pain is pain of psychological origin. Psychogenic pain is entirely or mostly related to a psychological disorder, such as hypochondria (health anxiety phobia). Psychogenic pain does cause physical pain. When individuals have persistent pain with evidence of psychological disturbances and without evidence of a disorder that could cause the pain, the pain may be described as psychogenic. Pain that is purely psychogenic is rare. Pain complicated by psychological factors still requires treatment, often by a team that includes a psychologist or psychiatrist. For most individuals who have chronic psychogenic pain, the goals of treatment are to improve comfort and physical and psychological function. Medications, including antidepressants, and psychological counseling are often used.