Ipad 2 year old screen light is brighter at centre area

The middle of the screen area has bright froth like lighting. Back light only has this problemz No other issues. The spread is increasing. Now it has covered 80 % of area. I stay in humid area. Since I travel a lot , I place it on table or shelf sometimes covered in leather bag and use it sparingly. Not fallen down or accidents. Will the screen absorb moisture from environment? No screen protector used. Photo attached. Pl help.