Macbook Pro Screen Stains/Spots

Hello everyone,

My Macbook has been growing some weird stains/spots in the screen. I can't tell if it's dust, humidity or whatever... I am careful with my computer and I keep it safely stored from any dust...

I'd like to ask you if it's an usual thing and if there is any way to fix this and/or stop it from growing. Please see the attached picture. Thank you in advance.