wow, googling itch was incredibly helpful.
the first line from wiki was also incredibly useful
"An itch (Latin: pruritus) is a sensation felt on an area of skin that makes a person or animal want to scratch it" no circular definitons there at all.
dictionary covered the same first line as wiki, at least that covers the linguistic portion of my question.
okay, i started off this response aiming to be really sarcastic, now I don't even know anymore.
but I found this link
http://science.howstuffworks.com/question600.htm
really helpful.
yeah it was a dumb question to begin with.