While both exfoliate on a chemical level, they do so in slightly different ways. First off, enzymes are tiny molecules found in fruits (think pumpkins, cherries, and papaya) that break down keratin – also known as the protein in dead skin cells. They remove those dead skin cells on the skin's surface, but they don't exactly promote cell turnover for living cells underneath. Think of enzymes as if they were peeling off already dead skin and buffing it smooth instead of forcing cells to turn over.
Acids, on the other hand, go deeper into your skin and speed up sales for all of your skin cells, not just the dead skin that sits on top: "Acids physically turn skin cells over (which can actually cause the skin to peel off), which enables the creation of new skin cells ", says the prominent beautician Lisa Guidi, owner of Erase Spa. Acids are also found in natural herbal products (lemon, apple cider vinegar, etc.), but they give a slightly more intense peeling than the average fruit enzyme.
"Imagine there is glue between the skin cells holding them together," explains double board certified dermatologist Melynda Barnes, M.D., clinical director of Rory – an online health service that creates customizable skin care formulas. "Enzymes break down this glue (the keratin protein), which allows the dead skin cells to be removed or peeled off the skin." Acids, on the other hand, "trigger cell death in older skin cells and encourage the growth of new skin cells. This causes older cells to peel off and newer skin cells to take their place."