The ability to bestow glow on demand has earned esthetician Shani Darden a cult following among celebrity devotees like Jessica Alba and Rosie Huntington-Whitely. At her state-of-the-art spa in Los Angeles, her signature method — a melding of ingredient-focused products and high-tech add-ons like LED therapy, microcurrent, and oxygen rejuvenation — has served as an incubation lab for her eponymous results-driven skin care collection. A staple in every client’s vanity? Her do-it-all hero serum Retinol Reform.