What is pain?
Pain is an unpleasant sensory and emotional experience, which we associate to actual or potential bodily damage. That is, pain is always a subjective experience. People learn and understand “what pain is” according to their experiences in early life.
It is possible to experience pain without any bodily damage or even underlying known cause. If someone reports a painful experience, we should consider the report as true. This definition is adapted from that proposed by the International Association for the Study of Pain (IASP), an international society founded in 1973 and leader in research, education and policies for the understanding and treatment of pain.
Good pain: A protection mechanism
Every vertebrate, from a fish to a gorilla, will react to injury or potential damage by withdrawing or moving away from the harm. Protective reactions to damage are among the oldest survival tricks in nature. Us humans, have also developed pain perception as part of our protective arsenal.
We have nerve cells capable of sensing tissue damage, which are connected to a network of cells in our spinal cord, brainstem and brain, which in turn can activate pain reducing mechanisms like muscle twitches (to move our body away from the source of pain), or can even produce our own internal pain medicine (these are special substances to reduce the transmission and experience of pain). An unpleasant sensation of pain is also tied into a brain learning mechanism for us to learn that certain scenarios are dangerous and to be avoided.
This is the good pain, a normal part of our sensory system, and as useful as vision or hearing, something that we are all born with and that we cannot live without. Good pain is protective. It makes sure we do not grab a hot dish, bite our tongues, or touch a needle (this type of pain is called nociceptive and is caused by the activation of our pain receptors or nociceptors).
The bad pain and chronic pain
Sometimes, individuals have abnormally elevated and persistent pain, in absence of injury. This is called “maladaptive” pain because it is no longer protective and leads to sensory irregularities and suffering. This is the bad pain. Pain is felt in the absence of injury or is triggered by processes that do not normally cause it. In addition, this pain is long lasting— and is considered to be chronic when it lasts beyond the expected time needed for healing or beyond a period of three months. This pain is associated to malfunction of the protective mechanisms that we mentioned above, leading to an over exaggerated response to incoming stimuli or perceived stimuli, and to a reduced protective response (eg. the body produces less internal pain medicine).