You are opening your mail. Your heart rate picks up as you grab letters that will undoubtedly have bills in them. You throw away all those annoying fliers that keep congesting your mailbox to no end. The familiar smell of envelope glue wafts through the air.
And to top it all off, you get a paper cut. Your favorite. And as you make it through the rest of your day, wincing and cursing at that momentarily forgotten paper cut you ask yourself - How can something so small hurt so much?
Hello I am Luc Boutin and we are the Alien Among You. Welcome to episode 4 and in this episode we are doing another Alien Dinner Conversation . Today we will answer that question exactly - what is about a paper cut that hurts so much?
Well before getting to that answer, we have to go over some much needed background. First, we have to understand how touch sensation is concentrated around the body.
As it turns out, not every part of your skin is equally as sensitive to touch as the next. As animals and humans evolved, we evolved to develop a greater sensitivity to touch in certain areas that give us a survival advantage.
For humans for example, we developed a higher concentration or sensitivity to touch on our hands, face, lips and tongue. Being social creatures, we may postulate that we likely developed this to help us communicate through spoken language and facial expressions. It probably also helped us with chewing and lip dexterity for eating a wider range of foods. As for our hands, the increased innervation allowed for finer sensory feedback to do detailed work with our hands. This probably helped us create complex tools and eventually led to modern technology as we know it today.
The relative organization and concentration of innervation is termed the sensory homunculus. You can look it up. It’s a strange illustration of a human where the body parts are shrunk or enlarged based on the relative concentration of innervation.
The hands, face, lips and tongue are huge on this illustration, while other body parts have been shrunk. It’s kind of cool but also super creepy to look at.
But anyhow, how does this relate to the paper cut thing? Well the same rich innervation that gives us great tactile feedback in the hands and fingers also works again us when it comes to pain.
It means you can literally feel more pain in the face, tongue, lips and hands than other areas. And since we handle paper mostly with our hands (unless you live some interesting alternative lifestyle, which if you did, no judgement) but since we handle most paper with our hands, most paper cuts happen on our fingers and hands.
That's part of the reason paper cuts are so painful – they mostly happen on our hands and our hands just happen to be one of the most sensitive areas on our body. We also use our hands every day so small cuts get pushed and scrapped against constantly, giving us daily jolts of pain.
The second part of the puzzle lies in the microscopic shape of paper. Paper seems to have a straight edge. But if you were to zoom in to see the edge of a piece of paper more clearly, you would see it’s more like a bunch of teeth sticking out in a surprisingly disorganized way. It’s like a tiny paper shark mouth. When a shape like this cuts your skin, it leaves more damage behind than if it were perfectly straight. More damage equals more pain.
And lastly, the final reason lies in in how pain is perceived and alleviated when our skin is cut. Our skin has many receptors that give all sorts of information. Some respond to pressure, cold, heat or pain – the ones were interested in today are obviously the pain ones.
They are called nociceptors. They turn stimuli that is damaging to our tissues into electrical signs that are interpreted by our nervous system and brain as pain. From an evolutionary perspective, this is paramount to survival. An animal that is incapable of feeling pain would have no way of knowing that they are doing things that are harming their own tissues. It’s hard to imagine such an animal surviving.
Our nociceptors will give us pain signals when pressure is too great, cold is too cold and when hot is too hot. But they can also react to chemical signals from surrounding tissues that are damaged.
When you get a typical cut, you bleed. That seems inconvenient, annoying, and for some unlucky people may even make them faint but the bleeding actually has an important function when it comes to these nociceptors.
Usually, when blood clots, it essentially covers these nerves ending with a cushion of clotted blood. This eventually leads to the formation of a scab. This cushion shields the free nerve endings from additional exposure to the outside environment and thus reduces pain.
A paper cut on the other hand is special. It’s special because it happens at the perfect depth. When you get a papercut that hurts you, it’s cuts you deep enough to reach past the very outside layer of the skin that has no nerve endings and reaches the layer where nociceptors are present.
This hurts. But it doesn’t cut you deep enough to trigger any substantial bleeding. Well without bleeding, you don’t get that oh-so-sweet-clotted-blood cushion that would shield these free nerve endings from the outside world.
So they remain uncovered. And an uncovered nociceptor is much easier to trigger. That’s why even the slightest scrape or pressure will cause a disproportionate amount of pain.
To summarize, a paper cut hurts so much because we evolved to have an increased concentration of innervation, and thus pain receptors, in our hands, because paper is apparently a formidable microscopic weapon and because paper cuts you deep enough to hurt, but not deep enough to bleed, clot and stop the pain.
So there you have it my fellow aliens, you now know why paper cuts hurt so much! The next time someone close to you get’s one, make sure to let them know why its hurting so much. I am sure in that moment that they will care greatly and really appreciate the lesson for why they are in agony.
I am Luc Boutin, We are the alien among you, have a great day and see you on the next episode.
Bibliography
https://www.britannica.com/science/homunculus-biology
Britannica entry on the motor and sensory humunculus
https://www.york.ac.uk/news-and-events/features/2019/social-skills-shape-modern-human-face/
Article on how human faces changed shape, muscles and innervation to communicate as social creatures
https://pmc.ncbi.nlm.nih.gov/articles/PMC8257305/
A paper on the history of the hand in humans
https://www.bbc.com/future/article/20160902-why-paper-cuts-hurt-so-much
A BBC article on way papercuts hurt so much
https://www.jci.org/articles/view/42843
Paper on how pain receptors work
