Please Note That Hot Whether Causes Oxidization Or Slight Leakage Of Pure Vitamin C21.5% Advanced Serum. You May Be Faced With Following Phenomena ; &Ldquo;Slight Leak, Hissing Sound, Gassy Bubbles" Since It Is Natural Phenomenon That Can Only Appear To Pure Vitamin. It Is Totally Safe To Use As Long As The Color Of Contents Is Not Dark Yellow Or Orange Which Means It Has Been Oxidized Already. So We Recommend Keeping The Serum In Cool Places/Fridge To Avoid Oxidation And Using It Within 6 Months Once You Got The Product. The By Wishtrend .Pure Vitamin C21.5% Advanced Serum Is A Vitamin Serum To Improve Overall Skin Tone And Texture. Containing Pure Vitamin C, It Is Free Of Parabens And Other Harmful Ingredients In Order To Decrease Irritation To The Skin. It Is Formulated With 10 Essential Ingredients For A Fast And Effective Result. 30Ml / All Skin Types / Made In Korea Cruelty free, Vegan Friendly, Ethanol free, Paraben free, Silicon free, Steroid free, Artificial Coloring free, Artificial Fragrance free.