Yes, LESIONS is a Scrabble word!

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

Is it a valid word?

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

any localized abnormal structural change in a bodily part
an injury to living tissue (especially an injury involving a cut or break in the skin)