Yes, PSILOSIS is a Scrabble word!

Letter values in Scrabble US: P 3, S 1, I 1, L 1, O 1, S 1, I 1, S 1.

Is it a valid word?

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

a chronic disorder that occurs in tropical and non-tropical forms and in both children and adults; nutrients are not absorbed; symptoms include foul-smelling diarrhea and emaciation
falling out of hair

Also: tropical sprue.