Dr. Courtney Rubin, our Chief Medical Officer, weighs in on your most pressing skincare questions.
Vitamin C can be used day or night, but I like to use vitamin C during the day because of its photoprotective properties (though, it is not a substitute for sunscreen). Many people use retinoids at night (because retinoids can break down in sunlight), and it reduces the risk of irritation to use retinoids alone at night rather than mixing them with other actives like vitamin C. This is why most people use vitamin C in the morning and retinoids at night, and this is the regimen I usually recommend.