get under one's skin vs get at

get under one's skin and get at both are verbs.

Word	Noun	Adjective	Verb	Adverb
get under one's skin	No	No	Yes	No
get at	No	No	Yes	No

As verbs, get at is a hypernym of get under one's skin; that is, get at is a word with a broader meaning than get under one's skin:

Other hypernyms of get under one's skin include annoy, bother, chafe, devil, get to, gravel, irritate, nark, nettle, rag, rile, vex.

get under one's skin (verb)	get at (verb)
irritate	cause annoyance in; disturb, especially by minor irritations
	reach or gain access to
	influence by corruption