In practical terms, retinol requires two conversion steps before becoming active; retinal (also called retinaldehyde) requires one; and prescription tretinoin is already retinoic acid. That generally makes tretinoin faster acting and more potent, but also more likely to cause irritation. Once converted into its active form, retinol gets to work on several signs of skin aging at once. As Dr. Ruth explains, it “increases cellular turnover, stimulates collagen production, improves skin texture, reduces fine lines, fades discoloration, and helps keep pores clear.” How to Choose the Right Retinol One of the biggest misconceptions is that a higher percentage automatically means a better product. The type of retinoid, the overall formulation, and how consistently you’ll actually use it matter far more. A high-strength retinol that irritates your skin so much you stop using it after two weeks won’t do ya much good, while a lower-strength formula you can use consistently almost always will. The format largely depends on your skin type. Dr. Ruth says serums are typically lighter and may appeal to those with oily or …