Getting active ingredients into the skin is the difference between cosmetic fluff and efficacy. Technically, cosmeceuticals are cosmetics and do not enter the skin; if they entered the skin, they would be classified as drugs, which would limit the tremendous ingenuity possible in cosmeceutical development. Not all cosmeceutical ingredients should penetrate the skin because some are intended to function on the skin’s surface while others theoretically must reach the dermis to actually achieve the optimal effect. For example, sunscreens should remain on the stratum corneum to either absorb UV radiation and convert it to heat or reflect UV radiation. A penetrating sunscreen formulation would be suboptimal, as UV entry into the skin could create reactive oxygen species before the sunscreen could act. In contrast, other ingredients such as antioxidants do not function optimally on the stratum corneum and should reside in the viable compartments of the skin where oxidative damage affects DNA.