Why Do You Rub Your Skin When You’re Injured? There’s Actually A Very Good Reason

The birth of a new theory

To understand what could be happening here, we need to journey back to 1965, and a seminal paper by Ronald Melzack and Patrick D. Wall. In it, the pair introduced the world to their new theory of pain, called the gate control theory. This was a major moment in neuroscience research. 

“[The] gate control theory of pain […] has since revolutionized our understanding of pain mechanisms and management,” wrote Joel Katz and Brittany N. Rosenbloom, marking the study’s 50th anniversary. 

“The gate control theory has had a major clinical impact on how pain is viewed by health care practitioners, how patients are treated, and, perhaps more importantly, it has provided patients with hope that pain relief is possible.”

Melzack and Wall’s paper came at a time of controversy in the field of pain research. There were two major competing theories at the time, widely held to be mutually exclusive. Melzack and Wall saw issues with both, but also points they agreed with; their new gate control theory was their attempt to synthesize all of their beliefs into one unifying theory. 

Like a lot of radical proposals, it’s fair to say it was not an instant hit with other scientists. It would be a number of years before it would gain broad acceptance. 

How does gate control work?

“Gate control theory posits that the sensation of a noxious stimuli can be blocked by a non-noxious stimuli carried by nerve fibers that reach the brain before the painful input because those nerve fibers are slower,” said pain specialist Dr Judith Scheman in an interview with Cleveland Clinic Health Essentials. 

In other words, a non-painful stimulus – like when you rub your shin after walking into a table – can overtake slower pain signals as they travel via the peripheral nerves and spinal cord to the brain. The result, according to the theory, is that you feel less pain.

Neuroscience students up and down the land will have encountered a diagram like this at some point in their studies. It’s a slightly more colorful version of the illustration in Melzack and Wall’s original paper.

The Aβ fibers at the top of the diagram are nerve fibers with a large diameter and an insulating myelin sheath along the outside. Because of this, they can transmit impulses more quickly than the narrower, unmyelinated C fibers at the bottom. And we’re talking way faster: about 386 kilometers per hour (240 miles per hour) for Aβ vs. a measly 3.2 kilometers per hour (2 miles per hour) for C fibers. 

There’s also a third type not shown in this particular diagram: Aδ, which sit somewhere in the middle but still on the slower side.

The Aβ fibers are the ones activated by non-painful stimuli, like normal touch and pressure. The Aδ and C fibers are the ones activated by pain and heat. 

In the version of the diagram above, the “gate” is closed. While the C fibers are firing, the Aβ fibers are too – and remember, they’re faster and more efficient. The Aβ fibers, in turn, stimulate the inhibitory interneurons in the center of the image, which have ultimate control over whether pain signals reach the brain. When they’re stimulated by the Aβ fibers, it produces an inhibitory response, blocking pain signals from getting through. 

This is all happening in the spinal cord, specifically the dorsal horn, a key waypoint on the journey of a pain stimulus to the brain. It’s here that the three different types of fibers link up with secondary neurons, and later – via a couple of complex neural pathways – to the central nervous system itself. 

Is the gate control theory all there is to it?

Most of us can attest from personal experience that there’s merit to the gate control theory – we’ve all done the “rub your bruised arm or leg” trick, and most would agree it really does help control the pain. Scheman explained that while this is partially down to simply distracting us from the injury, it is also at least partly because of gate control. 

But Melzack and Wall’s paper is now more than 60 years old, which is pretty ancient in biological terms. Recently, it’s been suggested that while the theory has its place, it may be time for an update to reflect all we’ve continued to learn since the 60s. 

“What progress have we made in our study of sensory processing and its modulation in the spinal cord since 1965?” asked Harvard Medical School professor Clifford J. Woolf in a 2022 paper.

“The reason we need to move on from the original gate control theory is that the model, while inspiring and of great historical importance, is we must now recognize, outdated and too simplistic.”

For example, Woolf explains, we now know that there are different subtypes of Aβ, Aδ, and C fibers, and we understand that the neuronal makeup of the dorsal horn itself is much more complex than was appreciated in Melzack and Wall’s time. 

Woolf does point out that the theory helped usher in new ideas about pain relief, which have been used successfully in thousands of patients. He also suggests that at least one of the original proponents of the theory would be thrilled at the prospect of updating it so that it can continue to help future generations of pain patients.

“I had the privilege of working with Pat Wall at the start of my career,” Woolf revealed, “and I know he would be as excited as I am at the prospect of a data-driven detailed understanding of the actual processing of sensory information in the spinal cord that drives pain, something that is, hopefully, at last imminent.”

But still, it’s fun to think that a simple action like rubbing or touching an injury – something most of us do subconsciously all the time – might be having a real impact on how pain is transmitted deep inside our nervous system.

All “explainer” articles are confirmed by fact checkers to be correct at time of publishing. Text, images, and links may be edited, removed, or added to at a later date to keep information current.