New and unopened! Crystal retinal serum in formula 3 (beginner strength). Full-sized - 1 oz. From Medik8: Discover youthful skin with Medik8 Crystal Retinal, the one-of-a-kind, ground-breaking serum that reinvented vitamin A skincare. Available in a series of progressive strengths to accompany you on your journey to Beautiful Skin For Life. KEY BENEFITS Retinaldehyde is the star of Crystal Retinal; a next-generation form of vitamin A that is proven to deliver results up to 11x faster than retinol[1]. Yes, this is retinAL, faster-acting than retinOL, the classic form of vitamin A.