Yes, IRRITATES is a Scrabble word!

Letter values in Scrabble US: I 1, R 1, R 1, I 1, T 1, A 1, T 1, E 1, S 1.

Is it a valid word?

IRRITATES is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

cause annoyance in; disturb, especially by minor irritations
excite to an abnormal condition, or chafe or inflame
excite to some characteristic action or condition, such as motion, contraction, or nervous impulse, by the application of a stimulus

Also: get to, get at.