Dr. Beth Goldstein prefers to apply her antioxidants as a base prior to the thicker Caire serum and it works well for her skin type. We at Caire recommend that you apply our serum (day and night) before any other serums or retinols (we suggest retinols at night).  Allow to the Caire serum to fully dry and then apply anything else afterwards.  We suggest it this way to help eliminate any potential skin reactions, however feel free to switch it up just like Dr. Beth depending on how your skin adapts to Caire.