While vitamin C is an unrivaled skin-lightening antioxidant, there is one (sometimes good) downside, which is that it’s notoriously unstable. If it is damaged (or oxidized) before it comes into contact with your skin, it will lose its effectiveness. Furthermore, oxidized vitamin C has the potential to cause irritation and blackheads.
“That’s the downside of vitamin C,” says Fernandez. “It can be unstable, which means it can be rendered ineffective by environmental factors (like too much light or temperature). At most formulations, the color will darken and it will have an incorrect balance between active ingredients and alcohol.”
So, how do you make sure your vitamin C levels stay steady? All you need to do is check the color and smell of the product, says Fernandez. If the color is darker than when you bought it (for example, if it turns dark brown) or has a slightly burnt smell, throw it away. It is no longer worth using. The reality is that it’s already oxidized and you simply won’t get the same benefits as before. To prevent this from happening, Fernandez recommends “make sure to store it in a cool place, away from direct sunlight or heat fluctuations.”
