If you’ve never heard of retinol, let me give you a quick rundown: it is a topical treatment that can help stimulate cell turnover, pushing healthier looking, smoother, and more radiant skin to the surface. Retinoids (the umbrella term for any cream derived from vitamin A) are some of the most well-researched and revered ingredients in the cosmetic industry, due to the fact that (when applied properly) they can combat a wide range of hard-to-treat issues, from dark spots, to wrinkles, to texture, to acne. If you’re wondering what the common thread in Chrissy Tiegen, January Jones, J.Lo, and Reese Witherspoon’s skin-care routine is, I can tell you right now: a good retinol.