Bad Skin Pure Vitamin C Powder

This is the Bad Skin Pure Vitamin C Powder, a failed beauty item. I heard that cosmetics containing Vitamin C darken in color and oxidize with use, causing the Vitamin C's effectiveness to diminish. I heard that using a powder type stabilizes the Vitamin C from oxidation and allows for more effective application to the skin, so I mixed it in and applied it during the toner or essence step. However, perhaps because the vitamin ingredients don't agree with me, my skin felt stinging and irritated.