We have all felt pain before, whether it was when you touched a hot stove, a very cold surface, or slammed your hand on the table. But, why do we feel pain? Is pain always bad? Can pain serve a protective role?
First, let’s discuss what is pain. Pain is an experience with physiological, cognitive, and affective qualities. It is an uncomfortable experience that can be associated with physical symptoms such as nausea and dizziness, and emotional symptoms such as depression, anxiety, and irritability.
In order to understand why we feel pain, we must first discuss the different types of pain.
There are two ways to classify pain.
The first is by its duration. Here there are two types of pain: acute and chronic pain.
Acute pain is temporary. It is a response to a specific injury or stimulus. Acute pain is the most common type of pain. It is also adaptive and protective, as it alerts the body of potential tissue damage and motivates the person to refrain from using the injured area, allowing it time to heal. This is how young kids learn whether things in their environment are harmful. Imagine if you didn’t feel pain. You would likely burn your hand or bite off your lips.
Pain is essential for survival.
Here’s a story of two young women who can’t feel pain:
Chronic pain, on the other hand, is a disease. Chronic pain lasts for a long time often more than six months. It may or may not occur in conjunction with actual tissue damage. It is maladaptive and is often associated with disease states such as cancer, chemotherapy, and fibromyalgia. Chronic pain is very common, about 1 in 5 Americans suffer from chronic pain. In fact, chronic pain is one of the most common reasons adults seek medical care in the United States. Chronic pain can lead to fatigue, depression, and memory impairments. It can also have severe impacts on the quality of life of those who suffer from it, as it can be a barrier to participation in school, work, and recreational activities. There are many medications that doctors can prescribe to manage chronic pain. Interestingly, exercise has been shown to not only reduce pain sensitivity, but also mediate many of the affective components of chronic pain, such as depression.
The second way to classify pain is by how it arises. Here, there are three types of pain: nociceptive, neuropathic, and inflammatory pain.
Nociceptive pain develops in response to a specific stimulus that either causes or has the potential to cause tissue damage. This can be extreme cold, heat, or mechanical stimulation, such as a pinprick. It is the most common type of pain. Acute pain and nociceptive pain are synonymous.
Neuropathic pain results from nerve damage that arises from injury or infection of the nervous system. It presents as a shooting pain. There are two kinds of neuropathic pain, central and peripheral. Central neuropathic pain is associated with injury to the central nervous system, which includes both the brain or spinal cord. While peripheral neuropathic pain is due to damage of a peripheral nerve, for example, a nerve in your arm or leg. Neuropathic pain causes activation of the immune system, which often makes the pain more intense.
After the onset of inflammation, neuropathic pain is now classified as inflammatory pain. Other causes of inflammatory pain include tissue damage and muscle weakness. Inflammatory pain by definition results from immune activation and leads to two things. First, it activates sensory neurons that normally won’t be active. This makes normally nonpainful stimuli painful, otherwise known as allodynia. An example of allodynia is when a light touch causes pain when it normally wouldn’t. Inflammatory pain also increases the firing of neurons that respond to potentially painful stimuli. This increases sensitivity to normally painful stimuli, otherwise known as hyperalgesia. Something like a pinprick which causes mild pain in a healthy human might cause severe pain in someone experiencing hyperalgesia. Most chronic pain is inflammatory.
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