intensify vs flare up

intensify and flare up both are verbs.

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

As verbs, flare up is a hyponym of intensify; that is, flare up is a word with a more specific, narrower meaning than intensify:

intensify (verb)	flare up (verb)
become more intense	erupt or intensify suddenly
make more intense, stronger, or more marked	ignite quickly and suddenly, especially after having died down
increase in extent or intensity
make the chemically affected part of (a negative) denser or more opaque in order produce a stronger contrast between light and dark