The Collaborative International Dictionary of English v.0.48:

Itchiness \Itch"i*ness\, n.
   The state of being itchy.
   [1913 Webster]

WordNet (r) 3.0 (2006):

itchiness
    n 1: an irritating cutaneous sensation that produces a desire to
         scratch [syn: itch, itchiness, itching]