retouch vs touch up

retouch and touch up both are verbs.

Word	Noun	Adjective	Verb	Adverb
retouch	No	No	Yes	No
touch up	No	No	Yes	No

As verbs, retouch and touch up are synonyms defined as:

retouch and touch up: alter so as to produce a more desirable appearance

retouch (verb)	touch up (verb)
alter so as to produce a more desirable appearance	alter so as to produce a more desirable appearance
give retouches to (hair)