- 2x more effective than retinol: The Silk Serum provides the smoothing benefits of retinol and beyond, adding moisture back into the skin and even soothing irritation. To find the hero ingredient, the R&D team at the Tatcha Institute searched high and low, testing efficacy against retinols and known alternatives like bakuchiol. They found the best results with a highly effective duo of plant-based retinol alternatives: upcycled cranberry extract and sea fennel, which act on the same factors as retinol to support natural skin turnover and give the look of collagen-rich skin.