It brightens! It kills zits! It smooths scars! It totally resurfaces your face to give you the skin of a baby! IT'S DIFFERIN! This over-the-counter retinoid (an umbrella term for all vitamin-A derivatives, including retinol) is the only active ingredient that's proven to speed up your collagen production to increase cell turnover, and, in turn, give you the skin of your dreams. It can be irritating at first, so start slow: Apply a thin layer to clean, dry skin one night a week for a week, two nights a week for two weeks, three nights a week for three weeks, and then every other night indefinitely.
Source : https://www.cosmopolitan.com/style-beauty/beauty/advice/g3017/how-to-get-rid-of-acne-scars/