Now that layering skin-care products has become the norm and new holy-grail serums and facial treatments are dropping daily, it can be tempting to pair them together in the hopes that they simultaneously work on your skin. Although this can sometimes be true (hyaluronic acid pairs well with a laundry list of things), in some instances you’re better off using them individually. Such is the case with retinol and vitamin C. As a refresher, retinol increases cell turnover and vitamin C is an antioxidant that helps protect skin’s barrier from environmental stressors. When both are used in a routine (albeit separately), they become what skincare.com consultant and California-based dermatologist Anne Chiu, MD, refers to as the “gold standard in combating anti-aging.” Ahead, she outlines how to effectively incorporate vitamin C and retinol into your skin-care routine. Use One in the Morning and the Other at Night“Apply vitamin C right after you wash your face in the morning,” says Chiu. She recommends it for daytime use because it’s when the skin is most exposed to the sun and pollution. Retinols, however, should be used in the evening because they can contribute to sun sensitivity and may degrade with sun exposure. Chiu also advises slowly incorporating retinol into your routine and applying them every other day to start. But Don’t Mix Them You should stay away from layering the two, though. According to Dr. Chiu, using retinol and vitamin C separately ensures the efficacy of the products and that your skin is receiving the most benefit. They work best in different ph environments, says Chiu, who adds that some formulations of vitamin C could even make the skin too acidic to stabilize some retinol formulations. In other words, layering the two can lessen the effect of both, which is the exact opposite of what you want these two powerhouse ingredients to do.And Always Wear SPF! Daily SPF is a non-negotiable, especially if you’re using skin-care actives like retinol and vitamin C. Chiu recommends daily sunscreen application even if you’re using a retinol at night because of the potential for increased sun sensitivity all around. Look for a formula like CeraVe Hydrating Sunscreen for Face Lotion, which contains ceramides that help to restore the skin’s natural barrier while also locking in hydration — a must to combat retinol’s potentially drying effects.Read MoreHow to Combine Vitamin C, Retinol and Hyaluronic Acid in Your Skin-Care RoutineSkin Sleuth: What is Vitamin C and How Does it Work? Starting Retinol Can Be Tricky — Here’s How to Survive the Adjustment Period