The causes of itch are varied and a probabily best thought of by considering causes both:
I was told a mnemonic for the non-dermatological caues of itch sometime ago and had wrote it on a peice of paper and forgot about it. I tried to recall it last week for a case but couldn't and neither could I find the piece of paper.
So in the interest of memory and helpfulness I though I would share it online.
There you have it! I hope you find a use for it sometime and if you cannot rememeber it you know where to come to find it.