I have normal/dry skin, so foundation never oxidizes on me. But in this thread a few people said they did have that issue with this foundation. I will say that this foundation runs at least a shade, if not two shades, light so definitely test it before buying. I normally wear NW13 and the NW 15 in this foundation is a little bit light on me (but I am pretty sure NW20 would be too dark). It is totally 100% sweat proof. I sweat a lot because of my medication, and the heat here, and I've never had a problem with this foundation. It just does not budge.