Many drugs can be applied to the skin without entering the blood how is this fact explained by the structure of the skin?

The skin acts as a barrier due to its outermost layer, the stratum corneum, which is composed of densely packed dead skin cells and lipids. This layer is designed to prevent the entry of substances, including drugs, into the bloodstream, allowing only certain small, lipophilic molecules to penetrate. Additionally, the presence of tight junctions between skin cells further restricts permeability. Therefore, many topical drugs can exert their effects locally without systemic absorption.