What is Pain?

An overview of its causes and types

Doctor examining patient in pain
Everyone experiences it, but what exactly is pain?. Photo © Hero Images/Getty Images

What is Pain?

According to the National Institute of Neurological Disorders and Stroke, more than 100 million Americans experience some form of pain that lasts from a few weeks to even years. Moreover, everyone suffers from pain temporarily at various times throughout their lives, whether due to a headache, an infected tooth, a cut or broken bone, etc. While it's easy to just think "pain is pain," the reality is far more complex.

The International Association for the Study of Pain defines pain as "an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage." In other words, while each of us can easily tell when some part of our body physically hurts, our pain cannot be objectively assessed or measured by others because only we know how it feels. A doctor cannot look at a patient, for instance, and know precisely what hurts, how badly, and what that pain feels like. Pain, therefore, is whatever the person experiencing it says it is.

Categories of Pain

Even though pain cannot be objectively measured, pain is divided into two categories:

Acute Pain: An acute pain generally comes on suddenly due to an injury, disease, illness, infection or inflammation. This pain often warns the person that some sort of bodily trauma has occurred—such as a broken bone, a cut, surgery, a burn, etc.—and the cause can therefore usually be determined and treated.

While an acute pain sometimes creates feelings of fear, anxiety and/or restlessness in the patient, the pain and any physical and/or emotional symptoms usually subside within a few hours, days, weeks or (at the extreme) within six months, depending upon the cause. If the underlying cause cannot be diagnosed or treated, however, an acute pain can develop into a chronic pain.

Chronic Pain: Ranging from mild to severe, chronic pain lasts for a long time—for six or more months up to many years—and is often associated with a life-limiting or -threatening illness. The persistence of chronic pain can prove debilitating for the patient in some cases and can cause other issues, such as feelings of depression, withdrawal and/or exhaustion, as well as the loss of mobility or independence.

While there are various methods to treat and manage chronic pain, sometimes the cause of the chronic pain cannot be diagnosed or treated.

How the Body Signals Pain

The central nervous system in the human body consists of the brain and spinal cord. A vast network of nerves (the peripheral nervous system) extends from the spinal cord into other parts of the body, such as our skin, muscles and organs. When some sort of bodily trauma occurs, such as cutting your finger while slicing an apple, microscopic pain receptors called nociceptors send signals along the periphery nerves in your finger to the spinal cord, which transmits this message to the brain.

There, the brain processes the information and rapidly triggers your physical, emotional and intellectual responses.

The nociceptors in our body detect injuries to our tissues, which can fall into two types. Somatic pain results from injury to our bones, joints or soft tissues, such as our muscles and skin. Somatic pain is usually localized and often described as sharp, dull, aching, throbbing or gnawing. Examples of somatic pain include bone fractures, metastatic cancer of the bone, tumors and arthritis.

Nociceptors also detect inflammation, distension or stretching of our internal organs, which results in visceral pain. This type of pain is generally not localized and is often described as aching, cramping, a "deep" pain or pressure. Examples include pain in the abdomen from a bowel obstruction, and pain in the left arm and/or jaw from an acute myocardial infarction (heart attack).

If the nerves themselves become damaged or cease to function in either the central or peripheral nervous systems, patients can experience neuropathic pain. This pain is often described as burning, tingling, shooting, stabbing or shocking. Injury to the brain, brain tumors, diabetic neuropathy, and herpes zoster are all examples of things that can cause neuropathic pain, which can prove more difficult to treat than nociceptive pain.

Pain and Palliative Care

A patient receiving palliative care and/or hospice services might experience different types of pain related to the underlying disease or the hospice diagnosis. This type of pain is usually defined as chronic pain and can either be nociceptive or neuropathic, but he or she might also experience acute pain. Some examples include pain from pressure ulcers (bed sores), injury from falls, or side effects from the underlying illness, such as internal bleeding secondary to liver disease.

Regardless of the type of pain, its severity or cause, palliative care and hospice are well equipped to treat it. Pain management is a primary goal of comfort care.


The International Association for the Study of Pain, www.iasp-pain.org

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