The appearance and health of the skin, the body's largest organ, significantly influence an individual's perceived attractiveness. It appears healthy when it glows and seems aged when it turns rough and becomes susceptible to diseases. For this reason, comprehension of the science behind human skin is the way to create cosmeceuticals that bridge the gap between cosmetics and pharmaceuticals. This chapter aims to provide all the details of the skin's anatomy, its cellular composition by layers, its important processes, and the main external stimuli with which the skin, as a barrier, interacts. The chapter also discusses recent dermatology findings and innovative technologies that have aided in the advancement of cosmeceuticals. To summarize, the above are the key elements of this chapter on the anatomy, physiology, and biological function of the skin.