Topical treatments work by delivering active ingredients directly to the affected area. The skin is composed of multiple layers, primarily the epidermis and dermis, which serve as barriers to protect internal tissues. For a topical treatment to be effective, it must penetrate these layers. Histologically, the epidermis is made up of keratinocytes, melanocytes, and Langerhans cells, among others. The penetration of active ingredients depends on their ability to traverse the stratum corneum, the outermost layer of the epidermis.
