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 oxidise [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 colour or smell. These are common indicators of chemical changes due to heat.

If you're slathering on retinol at all hours of the day in hopes of clear, youthful skin, dermatologist Mona Gohara, MD, advises you stop. "Retinol degrades in sunlight," Gohara said. "Ultraviolet light destabilises it so it isn't as effective." Because of the negative effect sunlight has on retinol, she recommends that you only use the powerhouse ingredient at night. Not only will it work its magic while you sleep, but it'll also be most effective and safe after it's been stored in a dark, cool environment.