A paper cut is usually short and shallow, yet it can produce a remarkably sharp pain. Paper contains no special painful toxin. The effect comes from the cut’s location, depth and repeated disturbance working together.
A paper edge is thin but microscopically uneven, so it can make a narrow, irregular split in the skin. The cut often reaches living tissue containing sensory nerve endings without going deep enough to destroy those pain-signalling structures over a large area. Fingers also support fine touch. Research shows that fingertips have high spatial acuity for both touch and pain, so a tiny injury can be located very precisely. This is more accurate than simply claiming that fingertips must contain more pain fibres than every other body site.
The finger then keeps moving. Typing, turning a page, washing or bending a joint can pull at the cut and separate edges that have begun to close. Pressure, air and water may stimulate the exposed area again. The injury therefore sends renewed signals rather than hurting only at the instant it occurs.
Pain intensity is not a direct scale of tissue damage. A shallow injury in a sensitive, frequently disturbed site can hurt greatly, while deeper damage does not necessarily increase pain in proportion and may disrupt sensation itself. This is an explanation of a general physiological mechanism, not a way to diagnose an injury from pain alone.
https://pmc.ncbi.nlm.nih.gov/articles/PMC3778751/
https://www.mcgill.ca/oss/article/did-you-know/paper-cuts-hurt-so-much-because-our-fingers-are-really-sensitive
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