A face serum is a lightweight, fast-absorbing skincare product with a high concentration of active ingredients designed to penetrate deeply into the skin to target specific concerns like fine lines, dark spots, or dullness. Unlike thicker creams that form a barrier on the skin’s surface, serums are formulated with smaller molecules that deliver nutrients and hydration more effectively to deeper layers. They are applied after cleansing and before moisturizing, which locks in the serum’s benefits.