Yes, SENSITISATION is a Scrabble word!

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

Is it a valid word?

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

the state of being sensitive (as to an antigen)
(psychology) the process of becoming highly sensitive to specific events or situations (especially emotional events or situations)
rendering an organism sensitive to a serum by a series of injections