itching vs itchiness

itching and itchiness both are nouns.

Word	Noun	Adjective	Verb	Adverb
itching	Yes	No	No	No
itchiness	Yes	No	No	No

As nouns, itching and itchiness are synonyms defined as:

itching and itchiness: an irritating cutaneous sensation that produces a desire to scratch

Other synonyms of itching include itch.

itching (noun)	itchiness (noun)
an irritating cutaneous sensation that produces a desire to scratch	an irritating cutaneous sensation that produces a desire to scratch