Yes, CHLOASMAS is a Scrabble word!

Letter values in Scrabble US: C 3, H 4, L 1, O 1, A 1, S 1, M 3, A 1, S 1.

Is it a valid word?

CHLOASMAS is a valid word in the official Scrabble dictionary (US) and the UK Scrabble Dictionary, but not in Words with Friends (ENABLE).

a tan discoloration of a woman's face that is associated with pregnancy or with the use of oral contraceptives

Also: mask of pregnancy.

Not playable in Scrabble US: MELASMA.