What does it mean when powder foundation oxidizes?

I've been wanting to get MACs Studio Fix Powder foundation for a little while now and have been watching a lot of reviews for it on youtube, but in many of the reviews they say it ';oxidizes'; (if im spelling that right) on your skin after awhile





Im not really sure what that means, can someone please explain that to me?





also, if you've used mac studio fix powder WITHOUT FLUID! (I dont like liquid foundation) do you like it?





Thanks!What does it mean when powder foundation oxidizes?
When the oils in your skin mix with the foundation and turns it darker and orangey.





A primer can help with this dilemma.What does it mean when powder foundation oxidizes?
it means it either gets darker after 30 mins or so or get orangey...