flare up vs flare-up

flare up is not a noun while flare-up is a noun.

Word	Noun	Adjective	Verb	Adverb
flare up	No	No	Yes	No
flare-up	Yes	No	No	No

flare up (noun)	flare-up (noun)
	a sudden intense happening

flare up (verb)	flare-up (verb)
erupt or intensify suddenly
ignite quickly and suddenly, especially after having died down