“Rub it better.”
We all know what pain feels like: a stubbed toe, an aching back, that sharp jolt when we touch something hot. We’d rather avoid it, yet without it life would be dangerous. Pain is one of the body’s most important protective systems.
But what exactly is it? Where does it come from? And why does it sometimes carry on long after an injury should have healed?
It’s not just about the injury
You might assume pain comes directly from an injured muscle, tendon, joint or bone. Not quite. Pain is an experience produced by the nervous system.
Throughout the body are specialised nerve endings called nociceptors. They respond to excessive pressure, extreme temperatures and chemicals released during inflammation, and send signals towards the spinal cord. Nociceptors don’t detect pain. They detect potential danger.
The spinal cord and brain then process those signals, together with past experience, expectations, emotions and everything else you’re sensing. The result may be the experience we call pain.
In 2020, the International Association for the Study of Pain updated its definition for the first time since 1979. It now describes pain as an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage. It also notes that pain and the nerve signals of danger are different things.
That’s why you can have considerable pain with little ongoing damage, or substantial damage with surprisingly little pain. Pain is a protective experience, not a measurement of injury.
Pain gateways: can we cheat the system?
Think back to childhood. You fall over, bang your knee and immediately rub it. Strangely enough, it often works. Why?
In 1965, Ronald Melzack and Patrick Wall proposed the Gate Control Theory of Pain: signals travelling towards the brain can be regulated within the spinal cord, as if they must pass through a gateway.
When you rub your knee, you activate touch and pressure nerves, which carry signals along larger, faster nerve fibres. These can switch on circuits in the spinal cord that reduce some of the pain-related traffic. It’s like turning down the volume. The injury hasn’t healed, but it hurts less.
The same principle helps explain why massage, pressure, vibration and TENS (electrical stimulation through the skin) can ease pain for a while. But the system is more sophisticated than a single gate: the brain also sends signals down to the spinal cord, turning pain up or down. Pain isn’t a one-way message. It’s a conversation between body, spinal cord and brain.
Inflammation: turning up the volume
Pain isn’t always from a sudden injury. Sometimes it builds gradually: an overworked tendon, an irritated joint, a shoulder that gets steadily worse.
Inflammation is often part of the story, and it isn’t the enemy. It’s an essential response that protects tissue and coordinates repair. Injured cells release chemical messengers, including:
TNF-alpha: involved in inflammatory signalling.
Interleukin-1 beta (IL-1β): another key regulator of inflammation.
Prostaglandin E2 (PGE2): makes pain-detecting nerve endings more sensitive.
When this signalling becomes excessive or prolonged, nerve endings start reacting more strongly to things that wouldn’t normally bother them. A movement that was comfortable becomes painful, so we move less. Over time that brings stiffness, weakness and lost confidence. Movement is often key to recovery, yet pain discourages the very activity that could help.
When the alarm stays on
Sometimes the system stays sensitive long after the original problem has settled. That’s more common than most people realise: a major review found that between a third and half of UK adults, roughly 28 million people, live with chronic pain, meaning pain lasting three months or more.
When to get checked
See your GP promptly if pain follows a fall or injury, wakes you at night, or comes with fever, unexplained weight loss, numbness, weakness, or changes in bladder or bowel control.
Turning the volume down
So pain can be turned up, and it can be turned down. In the next post, we look at whether light might be one of the ways to turn it down, and what the research actually says.
Sources
Melzack R, Wall PD. Pain mechanisms: a new theory. Science, 1965; 150(3699):971–979.
International Association for the Study of Pain, revised definition of pain, 2020: iasp-pain.org
Fayaz A et al. Prevalence of chronic pain in the UK. BMJ Open, 2016: doi.org/10.1136/bmjopen-2015-010364