The Real Reason A Paper Cut Hurts So Much
Over the millennia, human beings have evolved to be rather hearty creatures. We can survive a wide range of climates and temperature extremes; we have digestive systems that can deal with a wide range of plant, animal, and fungal matter; and our intricate immune systems can handle a lot of what nature throws at us. Yet, even a minor infection of the inner ear can cause an earache that's borderline torturous, and a common cold can cause us to miss work for a week.
But, one of the most unpleasant injuries a human being can experience, relative to its severity, is the humble paper cut. For an exceedingly minor superficial skin injury, a paper cut can produce a terrible sting that endures. As it turns out, evolution — the very force that caused Homo sapiens to be such resilient creatures –- is the reason paper cuts are so ridiculously painful.
Paper cuts usually happen on a busy part of the body
Think about the part of your body where you're most likely to get a paper cut. You're not going to get one on your abdomen or the back of your neck unless you're trying. As Mental Floss notes, you're most likely to get a paper cut on your hands or fingers, considering that you use those parts of the body when handling paper. Plus, the hands and fingers are busy parts of the body — being used to push, pull and grab all day long. In other words, you'll be continually re-opening the wound, prolonging the healing process and the agony.
According to Discover Magazine, the evolution of our hands and fingers was vital to our survival, and so it shouldn't come as a surprise that they developed more nerve endings and, thus, more pain receptors. All told, the hands and fingers are a terrible place to get an injury, even a minor one such as a paper cut.
Paper shreds the epidermis
In addition to the hands being just about the worst place on the body to get a paper cut, there's another factor that makes this injury so painful: the paper itself. As Wonderopolis explains, imagine you're using a kitchen knife to cut a piece of meat. A sharp knife will cleanly slice through the meat, while a dull knife will ultimately shred the meat. Humans are basically sentient meat and, as anyone who has worked in food service will tell you, knives do the same thing to human skin as they do to meat. A sharp one will produce a comparatively clean and painless wound, while a dull one will cause pure agony.
Paper is not designed for its sharp edges, and as such, when the edge of a piece of paper is pulled against the skin, it does not slice cleanly — it shreds. The damage may be microscopic, but your nerve endings don't care and will send plenty of pain signals to your brain.