Surfactants are compounds that reduce surface tension between substances, consisting of a hydrophilic head and a hydrophobic tail, enabling them to form micelles. They are classified into four categories: anionic, cationic, non-ionic, and amphoteric, each serving different functions in cosmetics such as emulsifying, solubilizing, and cleansing. While effective, some surfactants can be harsh on skin and hair, necessitating careful selection based on their properties.