What's in an itch?

November 2, 2005 6:28 PM

What is an itch, dermatalogically speaking? What's going on on your skin to cause it? Does it serve an evolutionary purpose?

I've always wondered what an itch actually _was_.

posted by toastchee to Health & Fitness (8 answers total)

Gooooooooogle to the rescue.
posted by kcm at 6:32 PM on November 2, 2005

Weird. Well, I'll try again.
posted by kcm at 6:43 PM on November 2, 2005

(I think that if you hit the link from Google, it gives you the full-text silently. At least, that worked for me - search "webmd itch", 10th result.)
posted by kcm at 6:45 PM on November 2, 2005

A doctor friend told me that most people have a greater tolerance for pain than itches. You scratch insect bites until they hurt because it feels better than the alternative.
posted by weapons-grade pandemonium at 11:14 PM on November 2, 2005

wikipedia to the rescuuuuueeee
posted by slater at 11:43 PM on November 2, 2005

I think an itch is often a great warning that something is wrong. Maybe you have a bug on you, (which could be deadly, especialy depending on where you live) or some other reason. Thats a good question though.
posted by JokingClown at 11:44 PM on November 2, 2005

More medical detail but perhaps more than what you're looking for.
posted by storybored at 7:48 AM on November 3, 2005

Evolutionarily, I think an itch signals something that won't kill you instantly, but might be harmful over long periods of time or repeated interactions. Your skin is usually your first line of defense in these situations, so a skin reaction would tell you that something bad is attacking you. The response is slow and low-level, so it doesn't trigger a flight-or-fight response, but rather requires some thinking. It helps you know what to stay away from. For example, you brush up against a 3-leaved plant in the woods, and a couple hours later have a red, itchy rash in the same area. You remember that this has happened to you before, or to other members of your tribe or family. Perhaps, you think, you should stay away from that three-leaved plant. Also, a broken piece of that big pointy smooth plant makes the itching stop when you rub it on the affected area, so that plant must be a good one.

Biologically, itches are pretty interesting. As some of the links above show, certain types of itches are carried along nerve fibers in the human body that are specific to itch/slow pain. These fibers have slower conduction velocities than the fibers that carry acute pain or trauma. The slow fibers are also inhibited fairly easily through scratching (which causes the axons to stop firing, thus the itch stops for a while.).
posted by sarahnade at 11:10 AM on November 3, 2005