I found an answer to that question here:
Papercuts are more painful because, due to all the stuff in paper,
some of it is left behind, in the wound when you get cut. Then, the
wound quickly closes in on itself, sealing the foreign matter inside.
The foreign matter stimulates pain receptors in your finger, causing
the stinging sensation.
There are also two additional components to this:
1) Paper isn't quite as sharp on the edge as, say, a razor blade,
(the comparison in the above web link). A dull blade will do more
damage to the tissue on a microscopic level than a sharp one; the dull
blade makes tiny rips and tears which hurt quite a lot and take longer
2) It may have a large psychological component. We don't expect
paper to hurt us, and we get angry and upset when it does. If we cut
ourselves with a kitchen knife, we fully expect it to hurt a lot and
take a long time to heal, and are more prepared to deal with the pain.
Paper cuts come unexpectedly, when we are engaged in what we think is a
low-risk activity, and we can get impatient with them when they heal
slowly. They may not even be worse than a cut with a kitchen knife. And
a serrated steak knife almost certainly will leave a worse cut.
Jason and Tom
(republished on 07/17/06)