Hello. Thank you for your inquiry. The purpose of products are similar. Not only is Cell Cycle Catalyst a daily exfoliant it also targets concerns with aging, discoloration. The Retexturing Activator is simply an exfoliant, so it's not necessarily a corrector like Cell Cycle Catalyst. Additionally, Retexturing Activator doesn't have any active ingredients which makes it most suitable for sensitive skin types. Cell Cycle Catalyst does have a 7.7% Multi Acid blend for more resilient skin. You sound like you have a good regimen, however I would only use either the Cell Cycle Catalyst (if you have discoloration) OR the Retexturizing Activator if you have sensitive skin. But, not both in the same regimen.

Hello. Thank you for your inquiry. Apply once a day, morning, or evening after cleansing and before serums. Apply 1/3 dropper with hands to a dry face. If using in the morning, apply before a SkinCeuticals vitamin C antioxidant serum and SkinCeuticals broad-spectrum sunscreen. In the evening, apply before serums and moisturizers. Depending on the content of your usual regimen (retinoids, other acids), should you feel any discomfort, space out the application of Cell Cycle Catalyst or switch usage of Cell Cycle Catalyst from the morning to the night (or vice versa) to avoid overapplication of active ingredients.