Can a moisturizer replace a serum for dry skin?

They serve different functions and work best together. Serums deliver concentrated active ingredients like hyaluronic acid or niacinamide in lightweight formulas that penetrate deeper into the skin. Moisturizers sit on top to seal those actives in and prevent transepidermal water loss. Skipping serum means your moisturizer has to do double duty, and skipping moisturizer means your serum evaporates before it can fully work.