A Complete Guide to Every Skincare Product You Should Keep Out of the Sun

Vitamin C is rich in antioxidants and works wonders on fading hyperpigmentation or dark spots. However, the ingredient is super sensitive to sunlight and heat, so if you have your pricey serums near a window or strong sunlight, consider moving them to a cool, dark space.

Dermatologist Michelle Henry, MD, told POPSUGAR that vitamin C can be easily changed and altered, especially by heat. "Heat and oxygen will oxidize [the formula] and break it down so that it's no longer as effective," she said. When it gets really hot, Dr. Henry said, many vitamin C products can even change chemical structure — and change in color or smell. These are common indicators of chemical changes due to heat.