concern vs touch on

concern is a noun but touch on is not a noun.

Word	Noun	Adjective	Verb	Adverb
concern	Yes	No	Yes	No
touch on	No	No	Yes	No

As verbs, concern and touch on are synonyms defined as:

Other synonyms of concern include bear on, come to, have to do with, pertain, refer, relate, touch.

concern (noun)	touch on (noun)
something that interests you because it is important or affects you
something or someone that causes anxiety; a source of unhappiness
a feeling of sympathy for someone or something
an anxious feeling
a commercial or industrial enterprise and the people who constitute it

concern (verb)	touch on (verb)
be relevant to	restore by replacing a part or putting together what is torn or broken
be on the mind of	have an effect upon
	refer to or discuss briefly
	be relevant to