Why Do We Get Chronic Pain? How Pain Works

The question I'm asked most often as a pain specialist is the simplest one: why do we get chronic pain? The answer starts with understanding how the pain system works when it's working properly — because chronic pain is what happens when that remarkable system malfunctions.

Your built-in alarm network

Pain begins at specialized nerve endings called nociceptors — you have millions of them in your skin, bones, joints, muscles, and internal organs, with perhaps 1,300 in a single square inch of skin. Different nociceptors sense different threats: sharp blows, heat, pressure, chemical changes, inflammation. It's as though nature sprinkled you with a variety of pain sensors, not only to report what kind of damage you're experiencing, but to make sure the message gets through on at least one channel.

Those signals travel along peripheral nerves to the spinal cord and up to the brain, relayed cell-to-cell by chemical messengers called neurotransmitters in less than a thousandth of a second. And the pathways differ: a fast express route reports the facts — where it hurts, how bad, sharp or burning — while slower, meandering pathways branch widely and fill out the pain picture, contributing to the emotional side of pain: fear, anxiety, anger. Specialists call that the "suffering" component, and it is every bit as much a part of pain as the sensation itself.

Touch a hot stove and you can watch the system's layers in action. A reflex circuit yanks your hand back before the brain has even received the message. The express route then delivers the facts to the thalamus, the brain's sorting and switching station, which routes them to the cerebral cortex — the thinking brain that assesses location and severity — and to the limbic system, which generates the emotion. Meanwhile the autonomic nervous system sounds a general alarm: pulse and blood pressure climb, pupils dilate, adrenaline flows.

The gate theory: why rubbing helps

Everyone has noticed that excruciating pain can sometimes be ignored — the quarterback who finishes the game on a torn ligament, the angler who lands his salmon and only then notices the bleeding gash on his leg. Observations like these led two researchers in the mid-1960s to propose the gate control theory of pain: specialized nerve cells in the spinal cord act as gates that open to let pain messages through or close to block them.

The gate can be closed from below — nerve cells that sense ordinary touch and pressure suppress the pain-carrying cells, which is why rubbing a sprained ankle or scratching near an itch genuinely helps (and why TENS units work). And it can be closed from above, by pathways descending from the brain itself — the mechanism behind the quarterback and the fisherman.

The brain's own opiates

The gate theory gained powerful support when scientists in Scotland and at Johns Hopkins asked a deceptively simple question: why does the human brain, the product of millions of years of evolution, come equipped with receptors that fit morphine — a plant-derived drug? The answer: because the brain manufactures its own morphine-like chemicals. Researchers found a whole family of them, now known collectively as endorphins — "the morphine within."

Endorphins are the currency of the brain's pain-control system. They're released by painful stimulation, they flow in the cerebrospinal fluid bathing the spinal cord, and they power the descending pathways that close the pain gate. Other chemicals push the other way: prostaglandins, released at injury sites, sensitize nerve endings (this is what aspirin and ibuprofen block), and a protein called substance P keeps stimulating pain nerves at the injury and in the spinal cord. Serotonin and norepinephrine help close the gate — which is exactly why certain antidepressants relieve pain independent of any effect on mood.

So why does pain become chronic?

Because every part of this system can malfunction. The thalamus normally sends a "message received — stop transmitting" signal back toward the injury; sometimes that mechanism fails and the alarm keeps ringing. Damaged nerves can fire spontaneously, without any injury signal at all. The spinal cord's gate cells can become sensitized — stuck open — so that ordinary touch signals get read as pain. Endorphin systems can become depleted, especially by poor sleep and chronic stress. And the limbic system's emotional circuitry can amplify everything.

In chronic pain, in other words, the alarm system itself has become the disease. That single insight drives everything we do at Newport Pain Management: the modern treatments that work — nerve-calming medications, targeted blocks, spinal cord stimulation, exercise, sleep restoration, and psychological therapies — work because each one targets a specific malfunction in this system. Understanding your pain is the first step to treating it.

Adapted and updated from patient education material originally based in part on National Institutes of Health publications. This article is for general education and is not a substitute for individual medical advice.