Happy to help. We recommend the conjunction of both vitamin C and hyaluronic acid to be used in your skincare routine. Vitamin C should be applied in the daytime as they help fight environmental aggressors and protect your skin from damage caused by free radicals that can contribute to atmospheric aging. Follow with the hyaluronic acid, which can be used in the AM and PM. If you are looking for product recommendations, we recommend SkinCeuticals C E Ferulic. This vitamin C serum is our award-winning antioxidant proven to deliver advanced protection against atmospheric aging and brighten skin complexion. It has also been formulated to meet the Duke Antioxidant patent parameters necessary for optimal vitamin C absorption and effectiveness. For hyaluronic acid, consider SkinCeuticals H.A. Intensifier. This serum is a multi-functional serum proven to amplify and maintain the skin’s hyaluronic acid levels to help restore the natural appearance of plumpness, smoothness, and firmness. Hope this is helpful.