Pain is an unpleasant sensation and emotional experience linked to tissue damage. Its purpose is to allow the body to react and prevent further tissue damage.
We feel pain when a signal is sent through nerve fibers to the brain for interpretation.
The experience of pain is different for everyone, and there are different ways of feeling and describing pain. This can makes it difficult to define and treat.
Pain can be short-term or long-term, it can stay in one place, or it can spread around the body.
Fast facts on pain:
Here are some key points about pain. More detail is in the main article.
Pain results from tissue damage.
It is a part of the body’s defense mechanism. It warns us to take action to prevent further tissue damage.
People experience and describe pain differently, and this makes it hard to diagnose.
A range of medications and other treatments can help relieve pain, depending on the cause.
Pain can be chronic or acute and take a variety of forms and severities.
Pain is felt when special nerves that detect tissue damage send signals to transmit information about the damage along the spinal cord to the brain. These nerves are known as nociceptors.
The brain then decides what to do about the pain.
For example, if you touch a hot surface, a message will travel through a reflex arc in the spinal cord and cause an immediate contraction of the muscles. This contraction will pull your hand away from the hot surface.
This happens so fast that the message doesn’t even reach the brain. However, the pain message will continue to the brain. Once there, it will cause an unpleasant sensation of pain to be felt.
How an individual’s brain interprets these signals and the efficiency of the communication channel between the nociceptors and the brain dictate how people feel pain.
The brain may also release feel-good chemicals such as dopamine to counter the unpleasant effects of the pain.
Researchers estimate that pain costs the United States (U.S.) between $560 billion and $635 billion each year in treatment costs, lost wages, and missed days of work.
Pain can be acute or chronic.
Acute pain is generally intense and short-lived. It is the body’s way of alerting a person to an injury or localized tissue damage. Treating the underlying injury normally resolves this type of pain.
The body’s “fight-or-flight” mechanism is triggered by acute pain, often resulting in faster heartbeats and breathing rates.
There are different types of acute pain:
Somatic pain is superficial pain that is felt on the skin or soft tissues just below the skin.
Visceral pain originates in the internal organs and the linings of cavities in the body.
Referred pain is felt at a location different to the source of tissue damage, such the shoulder pain felt during a heart attack.
Chronic pain lasts far longer than acute pain. It often cannot be resolved. It can be mild or severe, it can be continuous, as in arthritis, or it can be intermittent, as in migraines. Intermittent pain occurs on repeated occasions but stops in between.
The “fight-or-flight” reactions eventually stop in cases of chronic pain, as the sympathetic nervous system that triggers these reactions adapts to the pain stimulus.
If enough cases of acute pain occur, they can create a buildup of electrical signals in the central nervous system (CNS) that can overstimulate the nerve fibers.
This is known as “windup,” a term that compares the accumulation of these electrical signals to a windup toy. Winding a toy with more intensity leads the toy to run faster for longer. Chronic pain works in the same way. This is why pain may be felt long after the pain-causing event.
There are other, more specialized ways of describing pain.
Neuropathic pain: This follows injury to the peripheral nerves that connect the brain and spinal cord to the rest of the body. It can take the form of electric shock-like pain, tenderness, numbness, tingling, and discomfort.
Phantom pain: occurs after the amputation of a limb and refers to painful sensations given out by the missing limb. It affects some 70 percent of amputees.