When trying to answer the question of "What is pain?", I think we can start with a general definition of pain. The International Association for the Study of Pain (IASP) is a world organization focused on supporting the study and practice of pain and pain relief. Using their most recent definition revised in 2020, pain is
“an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage.”(1)
This seems to be a generally accepted description of pain. Though, I don't feel as though tissue damage is the only pain signaling threat. It is only the physical portion of the human. I'm a believer that the mental and emotional portions can also be threatened for a person to experience pain. For completeness, I've updated the definition to replace the term "tissue" with "body" as in the physical form. I've also included the mind and spirit. The mind and spirit are inherently part of the human experience and can loosely correspond to the psychosoma and psyche in the Western medical paradigm.(2)
In any case, I would like to broaden the definition to say that pain is
" an unpleasant experience that is actually, or perceived to be, damaging to the experiencer in body, mind, and/or spirit."
Note that my definition is similar to the IASP version, but broadening the concept to include not just tissue damage, but emotional and spiritual damage as well.
The Purpose of Pain
Pain is a warning system. It is one of the body's main protection mechanisms for self-preservation. It signals the brain that there is something threatening the organism.
Your pain mechanism signals you when something is harmful or dangerous. Luckily, it has the capability to warn you before injury occurs. Pain will also intensify as the potential for greater harm increases. The unpleasant sensation and discomfort from pain tells us that we should move away from the experience or mitigate the discomfort before further damage or injury occurs.
The Sensation of Pain
Pain is described an unpleasant sensation. So, what does pain feel like? It's subjective, so pain feels slightly different to everyone. But we can generalize to an extent what some negative sensations feel like. Descriptions of pain have been associated with the following terms:
Though not exhaustive, the above list are a few of the more common ways to share one's experience of pain. These sensations will overlap and it is possible to feel alternating, or multiple sensations at once.
Types of Pain (Time Based)
The temporal types of pain, or types of pain with respect to time, are acute pain and chronic pain.
Acute pain can be described as a painful sensation of short duration, usually due to a specific injury or event. Acute pain can be caused from falling off a bicycle, having knee surgery, or breaking a bone. After the injury, or event, the pain diminishes and eventually goes away.
Chronic pain can be described as a painful sensation that recurs frequently, varies in intensity over time, and sometimes has no specific injury associated with it. Some of the examples of chronic pain are lumbago, arthritis, or migraines. The timeline for chronic pain is a few months to years, and even decades.
Types of Pain (Source Based)
The nontemporal, or non-time based, types of pain are: nociceptive, neuropathic, and radicular pain.
Nociceptive pain is caused by an injury to the body tissues. Examples of this type of pain would be: spraining an ankle, getting a paper cut, or breaking your toe on a coffee table leg. This would be considered pain from physical injury or trauma, but would also include something such as pain from arthritis, or cancer. This would be the most common type of pain.
Neuropathic pain is pain due to an issue with the nerve itself. Whereas nociceptive pain is a pain sensation from tissue damage, neuropathic pain is a pain sensation from nerve damage.
Radicular pain is pain where a spinal nerve gets inflamed, compressed, or irritated in some way. The resulting pain can traverse the length of the nerve fibers and be numbing, tingling, or present as muscular weakness. Though both are nerve pains, radicular pain is physical damage to spinal nerves, whereas neuropathic pain is an umbrella term that includes radicular pain as well as other forms of nerve pain, such as: diabetic nerve pain, alcohol-related, chemotherapy induced, etc.
Note that the above categories are general and capture the majority of pain types that exist. Of course, all pain conditions will be best represented by a combination of time and non-time based pain types and this is perfectly normal.
How Pain Works in the Body (Nociceptive)
The definition of pain includes an unpleasant feeling. Now, we all have slightly differing ideas about what unpleasant is, especially as we go from an extreme sensation toward the mild end.
As the experience varies, the mechanism of pain signaling is the same. That is, the mechanism is the same until the signal gets to the brain. I'll try to oversimplify here without losing the integrity of the discussion.
We have sensors in our skin called nociceptors. The prefix noci- is Latin for hurt. Essentially, nociceptors sense things that could hurt you. These nociceptors sit at the end of the nerve and wait around for something to stimulate them. Nociceptors are able to sense temperature, pressure, and chemical stimuli.
When the nociceptor is triggered by potentially harmful stimuli, the signal is sent towards the brain using the central nervous system.
Once the pain signal notifies the brain, it is up to the brain to decide how threatening and how painful the burn, in this case, should be. This the perception of pain and how you think about this determines how the pain feels. This is the normal function of a nociceptive pain response and the main discussion in this article.
In the case of an extremely threatening signal from the nociceptor, the central nervous system (CNS) responds instead of the brain. Although your brain may be as fast as Einstein's, when you bypass thinking about whether or not a hot stovetop will burn you, you will possibly save more skin. This reflexive action causes you to jerk your hand away, lick your wound (if any), and admire your cat-like reflexes.
This secondary warning system is a great feature and it's sole purpose is to save time in the hope of preventing serious damage. This is not quite part of the discussion here, but I noted it to make sure you, the reader, understands that this is a slightly different pain response.
How Pain Works in the Brain
Have you ever gone to the doctor for knee pain only for it to hurt much worse while you are in the waiting room? Or have you ever had elbow pain disappear while you're enjoying your favorite tennis players on TV? I'm sure you've heard war stories where limbs have been blown off and the soldier doesn't feel anything until after he or she has left the battlefield.
No one has an explanation for how this happens and I'm not going to profess to know exactly how pain works in the brain either. The brain does not have a specific location to process pain. Unlike other sensations associated with specific areas in the brain, such as vision, touch, and hearing, there is no one specific cortical area dedicated to pain.(3)
We understand some of the locations that assist in cognitively assessing pain, but we don't have all of the pieces nor do we know exactly what the puzzle is supposed to look like when complete. As we study more, we gain some relevant research data that keeps refining our picture of pain in the brain. I'll share what I find interesting and try to make it consumable without too much detail.
Let's look at the beginning of the path. When the brain receives the pain signal, it gets to choose whether the signal is pleasant or unpleasant. One study has shown that a group of neurons in the amydgala of mice, specifically the basolateral region, were responsible for slapping a pleasant or unpleasant sticker on the pain signal.(4)(5) What makes this research significant is that the pain signal by the body only gets assigned "unpleasant" after it reaches the brain. Until then, it's a stimulus response neither good or bad.
Once inside the brain, the pain signals seem to frequently light up a "pain matrix" consisting of the anterior cingulate cortex, thalamus, and insula.(6) Unfortunately, there is also evidence that these brain centers are active during non-pain related stimuli. The ability of the brain to process information in different ways has added to the complexity of fMRI scanning.
The perception of pain for individuals is different and can be influenced by a number of factors, including: genetic, developmental, familial, psychological, social and cultural variables(7).
Given the above examples, there is a definite influence of the mind on pain. This subjective influence can't be measured precisely, but we try our best to describe pain with words and pictures, sort of like we are doing in this article!
The brain ultimately gets to decide what pain "feels" like. Your thoughts can dictate the intensity of the experience. The power of the mind cannot be understated. Everyone has some ability to control their thoughts, and this can provide powerful pain relief when used to your advantage.
How to Measure Pain
Given the above examples, there is a definite influence of the mind on pain. This subjective influence can't be measured precisely, but we try our best to describe pain with words and pictures, like what we are doing in this article!
The pain scale(8) is one way we can get closer to quantitatively measuring someone's pain experience. If you've ever been to the doctor's office, you've probably been asked "What's your pain like on a scale of 1 to 10?" The problem is that your 5 could be someone else's 10, or vice versa. The scale is subjective and based upon what you believe a 1 and 10 are. Now, if your worst injury is a papercut, you'd probably assume that it would be a 10 on the scale. While there is nothing wrong with that, the scale doesn't make much sense from person to person, but it does have value for yourself when you compare your current pain against any other pain you've had previously.
Since we continue to evolve the measurement of pain, variations of pain assessment scales (PAS) have tried to be more thorough. Some of the more commonly used PAS are: numeric rating, Wong-Baker Faces, McGill Questionnaire, Mankoski, and Brief Pain Inventory. Just remember that no perfect tool currently exists and that the data from the pain scale should only be used as a rough measurement tool for your level of pain.
What if I Never Felt Pain?
You may think that being unable to feel pain would be amazing, but it's not. Pain alerts you of impending danger. Without any warning signal, you wouldn't pull your hand off a hot stove until you either saw damage or smelled it. Eating finger foods could actually include part of your own finger! Injuries would be more frequent and more significant, because the warning wouldn't come before the tissue damage occurred.
There is a rare condition called congenital insensitivity to pain (CIP), where a person does not feel pain(9). These people struggle with self-inflicted wounds and have trouble navigating the various threats in the world around them. Unfortunately, the lifespan of CIP sufferers is drastically reduced and the majority die from injury in childhood.
The ability to feel pain is incredibly important to survival and should be seen as a tool, rather than a nuisance. If the pain mechanism is not operating correctly, it can show up as chronic pain, increased sensitivity to pain, and more. Therefore, managing your pain mechanism properly is a key to being able to assess the potential for injury correctly.
What Happens When Pain Signals Go Haywire
You can imagine that the pain mechanism in the body is perfect. But, it isn't. Between the skin and the spine, you may have a chemical imbalance triggering an action potential for a pain signal unnecessarily. Or your brain may attach an "unpleasant" quality to almost every muscle contraction and toss you into the group of fibromyalgia sufferers. There are plenty of ways for the pain signaling system to malfunction.
Many times, a malfunctioning pain response will become chronic pain. In these instances, pain just doesn't go away. It turns into a chronic pain cycle, which means that you are in a recurring loop until you find a way out.
The chronic pain cycle tends to require a multi-pronged approach that addresses the mind, body, and spirit. Physical therapy tends to be the most sought after solution, but I believe that in chronic pain, there is almost always a significant mental barrier that needs to be broken down. Unfortunately, the power of psychotherapy in breaking the pain cycle is underutilized. This can cause the physical therapy to seem ineffective.
In every case, I believe that an early, thorough pain management plan will more easily break a pain cycle than a fragmented, single focus treatment modality. Get treatment as soon as possible.
Pain is complex. It is also universal. Everyone will interact with a painful stimulus at some point in their life, except for those rare individuals suffering from CIP. Even though the experience of pain is slightly different for everyone, pain is a guide to help you assess threats to your life and limb. It is an innate warning system designed for your safety.
Knowing the types of pain that you can have will help you determine whether your condition is acute or chronic, physical or psychological, or some combination thereof. Remember, pain doesn't usually fall squarely into one category.
Every pain condition is different and being able to describe your situation will go far in letting doctors and other medical professionals help you to find a solution. Arm yourself with commonly used pain terminology and try to classify the pain that you have according to the scales available for pain assessment. The better you can verbalize and quantify your pain, the more clearly everyone can understand what you are dealing with. Plus, it may even help you to solve your pain problem yourself!
The psychological component to pain along with your mindset will influence whether a stimulus is pleasant or unpleasant. Your mind can also determine the intensity and duration of pain. Learn to treat pain as a passing event. Nurture your body as it heals and own the lesson after the pain, not the pain itself.
When the pain mechanism goes haywire, there are physical and psychological tools available for you to break the pain cycle, reduce your pain levels, and heal. Do not be afraid to challenge yourself and get out of your comfort zone in dealing with pain. Resetting the nervous system is an important part of the pain management mechanism and will go a long way in preventing a vicious chronic pain cycle. I cannot stress enough how important it is to manage pain as soon as injury occurs. Good luck!
2. The mind and spirit are considered one and the same in some circles, but for the purpose of this article, I've defined the mind as the object carrying out rudimentary management of body systems and the spirit as the higher level thoughts independent of bodily functions. Note that spirit in this context is non-religious.
3. Ahmad AH, Abdul Aziz CB. The Brain in Pain.Malays J Med Sci. 2014;21(Spec Issue):46-54.