The Itch is an article from The New Yorker on the neurology behind that annoying sensation we’ve all had.
I warn you, the article is quite icky in places, with a particularly stomach churning case study in one place, but I was quite fascinated to find out that the sensation of the itch seems to rely on itch dedicated nerve cells, distinct from the nerves that transmit pain.
One of the most interesting things is that itch seems to be one of the sensations most sensitive to psychological state. For example, I guarantee you’ll feel more itchy just reading the article (and probably already reading this).
via Mind Hacks
Edit: Kottke has written a good review of the article that is worth your time.