One of the most astounding breakthroughs in skincare science has to do with exfoliation. Exfoliation is more than just removing old dead cells for smoother skin and clearer pores. Through the science of "hormesis" we have learned that by gently stressing old cells you send a message deep into the skin to make newer, healthier, younger looking cells.
AHAs (alpha hydroxy acids) are top down exfoliants. They dislodge dead cells on the skin's surface and clear the pores by dissolving bonds that stick these cells together. AHAs offer instant gratification by providing a smoother, softer, more even texture.
Retinols are bottom up exfoliants. They work by filtering through the skin and stimulating cell production both in the dermis and the epidermis. As new cells rise to the top older cells are pushed off. This leaves cell layers more organized and youthful looking. At the same time chemical messengers stimulate fibroblasts to produce more collagen and other skin supporting structures. That means more firmness and less wrinkles.