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What Is Pain? 

Written by Teo Buzas, PT, DPT

Our understanding of pain tends to be straightforward. For example, I drop something heavy on my foot and it hurts. Pain equals injury, and the more pain I have the more injury there is. Experiences such as this are easy to understand and support the belief that pain is an indicator of tissue health. Pain is considered an input, a sensation that we feel caused by tissue injury. In this outdated pain model, pain is caused by injury and increased pain means increased damage. However, we now know that pain is not as straightforward. This new pain model states that pain is not an input. Pain is a complex, multifaceted output of the brain. Tissue damage is just one input into the brain’s output of the pain experience.

It is now widely acknowledged that the experience of pain is not simply an incoming message regarding tissue “damage” from the periphery. The pain experience reflects the person’s assessment of how dangerous a particular input is, based on not just the intensity of the input, but also the person’s prior experiences, beliefs, and contextual factors (1).

Let me provide some examples that will help with the understanding of pain as an output. It is much like hearing or seeing. We do not have special receptors in our ears for hearing. We have receptors that sense vibration and pass that information to the brain. Our brain creates our sense of hearing. We do not have special receptors in our eyes for vision. We have receptors that sense light and pass that information to the brain. Our brain creates our sense of vision. Pain is also an output of the brain. We do not have special receptors in our tissues for pain. We have receptors that sense chemical, mechanical, and thermal changes. These receptors are called nociceptors. This information goes to the brain, and in combination with other factors, our brain creates the output of pain. Pain is a decision by the mind based on the perception of threat (actual or potential) (2).

Pain is produced when the mind concludes there is danger and action is required. Pain can occur in the presence of tissue damage. Pain can occur in the absence of tissue damage. You can have tissue damage in the absence of pain. This is in opposition to what a lot of people have come to believe about pain. It is not something that is always understood quickly and accepted. Please, re-read those last three statements. Now, consider some examples you have seen or heard of that may be true of those statements.

Consider this image:

How painful was this?

In this case, the patient complained to doctors about hearing loss. Not pain. With imaging, they soon found a nail lodged in his brain. The man forgot about when this accident happened on a construction site, years prior, because he was drunk when it happened. He claims to have felt no pain and just rubbed herbal ointment on the injury at the time.

There are more examples like this. Consider the case of a man who walked into the emergency room with a nail stuck in his boot. The medical team tried to remove the boot, however, it was too painful. He was given heavy pain medication, and eventually, they were able to remove the boot. They found the nail had gone in between his toes and did not damage any tissue. Pain is complex. It involves a combination of multiple physical and non-physical factors. Pain is complex. It involves a combination of multiple physical and non-physical factors.

Common Sense Model framework (3):

Many areas of the brain activate during the experience of pain. Ongoing pain is not necessarily due to damaged tissue but could be from a sensitized state of the nervous system (4).

When the nervous system is more sensitive, you get more pain with less stimulus. There are physical/chemicals reasons for this. It is called a complex process termed central sensitization. This is an increased sensitization of pain modulating systems in the central nervous system (6).

Think of pain like an alarm (5). Now consider a car alarm. It usually takes a good amount of movement to a car (like someone breaking into it) for the alarm to go off. Have you ever walked by a car and the alarm went off? Due to some movement, the alarm triggered. That is a sensitive alarm system. The car was not being broken into.

When we have tissue injury, multiple chemical/physical changes happen that increase the sensitivity to that area. We naturally avoid bumping against that sensitive area. This is a protective mechanism that we have, and it is good.

However, when the pain becomes chronic (read “Chronic vs Acute Pain”) it changes the way the body and nervous system works because the nervous system is on high alert for prolonged periods. This is a sensitive alarm.

This is an image of the pain experience depicted as an alarm, before and after surgery. You can also think in terms of before or after tissue injury. Consider though, that pain sensitivity can also be affected in the absence of injury. Besides tissue damage, what else are potential contributors to the experience of pain? When you are on high alert for pain, there is an increase in cortisol levels which can lead to:


  • Fatigue
  • Irritability
  • Increased blood pressure
  • Foggy thinking
  • Poor sleep
  • Suppressed immune system
  • Anxiety


There are other factors that can increase the sensitivity of the nervous system and your soft tissues, increasing the likelihood of experiencing pain:

  • Previous failed treatment
  • Family concerns
  • Fear and anxiety
  • Persistent pain
  • Job issues
  • Different medical explanations


I have found the water/cup analogy from Greg Lehman helpful to think of pain and recovery. Think of pain and recovery in terms of a cup and water. If the cup gets filled and overflows, you experience pain. Now imagine that the water getting added to the cup is made up of things such as: stress, injury, worry, anxiety, poor sleep, anxiety, and habits.

Much of the focus has been put on taking or eliminating water out of the cup. This is important. But what about trying to make the cup bigger? If the same amount of water gets added, the cup does not overflow, and pain is not triggered. Another important part of the recovery is building a bigger cup. What can you do to build your cup? Consider factors in multiple domains: cognitive, emotional, social, physical, lifestyle (1).


At Bridging the Gap Physical Therapy, we are here for you. We offer full body evaluations and discuss your treatment plan. This includes your diagnosis, your goals, and the plan for getting you there. Find out more by speaking to our team today at 239-676-0546.


  1. O’Sullivan PB, et al. Cognitive Functional Therapy: An integrated behavioral approach for the targeted management of disabling low back pain. Phys Ther. 2018;98:408-423.
  2. Merskey, H. & Bogduk, N. (Eds.) (1994). Classification of chronic pain (2nd edn). IASP Task Force on Taxonomy. Seattle: IASP Press.
  3. Caneiro J, Bunzli S, O’Sullivan P. Beliefs about the body and pain: the critical role in musculoskeletal pain and management. Brazilian Journal of Physical Therapy 2021;25:17-29.
  4. Louw A, Diener I, Butler DS, Puentedura EJ. The effect of neuroscience education on pain, disability, anxiety, and stress in chronic musculoskeletal pain. Arch Phys Med Rehabil. 2011 Dec;92(12):2041-56.
  5. Saab CY, Waxman SG, Hains BC. Alarm or curse? The pain of neuroinflammation. Brain Research Reviews. 2008;58(1):226-235.
  6. Van Wilgen CP, Keizer D. The Sensitization Model to Explain How Chronic Pain Exists Without Tissue Damage. Pain Management Nursing. 2012;13(1):60-65.