Pain serves to signal a dysfunction in the body. It plays a useful role as an alarm signal, alerting the individual to take action against an abnormal situation.¹
Pain can be considered a sense, just like sight, hearing, or touch. When an internal or external aggression occurs, the body needs to be informed in order to react quickly. This is where pain comes in: it informs the body of any impact or injury it has sustained.
The pain message originates from specialized receptors scattered across the skin and most internal organs: nociceptors. Their function is to send a nerve signal to the brain to indicate potential damage. For example, when we place a hand on a hot surface, the nociceptors are activated and send a signal via specialized nerves up the spinal cord to the brain. At this point, it is not yet pain but an informative nerve signal called nociception.
Once the message reaches the brain, it is interpreted (location, severity, sensation) and modulated depending on emotional state, memories, past experiences of pain, and health condition. After this processing, the brain determines whether the damage is serious and whether a response (flight, defense, cry, tears…) is needed. Returning to the example of the hand on a hot plate: the brain interprets the signal as pain, but the hand would already have withdrawn due to a reflex arc in the spinal cord.
Within the nervous system, various mechanisms regulate pain intensity. As the pain message travels through the body, its intensity can be increased, reduced, or even blocked by regulatory systems. The Gate Control Theory, developed in 1965 by R. Melzack and P.D. Wall, explains how pain signals pass through a gate in the spinal cord, which can open or close depending on the activation of different nerve fibers—facilitating or blocking the signal.
For example, applying cool water to a burn or rubbing the skin after a bump stimulates certain fibers that block the signal and soothe the pain.
Acute pain acts as a useful alarm signal. However, when prolonged, it can alter the functioning of the nerves that transmit the signal to the brain, making the passage easier. This pain may then become persistent or recurring, potentially turning into chronic pain—defined as pain lasting more than 3 months. At this point, it loses its warning role and becomes a condition in itself: “pain as disease.”