Most Vitamin C serums will inevitably turn into a coppery brown colour when it’s exposed to sunlight, heat, and air due to oxidization. However, this change of colour is also a way to prove the pureness of your Vitamin C serum. By Wishtrend’s Pure Vitamin C21.5 Advanced Serum contains 21.5% of Vitamin C, which is highly concentrated, thus it’s suggested to keep the serum refrigerated once opened. This also makes it perfect to combat hyperpigmentation, discolouration, acne scars and dull skin! By Wishtrend has even improvised this formula to be non-sticky and more effective with it’s newly down-sized list of ingredients.