Surface-active agents, commonly known as surfactants, are compounds that reduce the surface tension between two substances, such as liquids or solids. They are often used in cleaning products, detergents, and emulsifiers to help mix oil and water, allowing for better cleaning and stability of mixtures. Surfactants have a unique molecular structure with a hydrophilic (water-attracting) head and a hydrophobic (water-repelling) tail. This dual nature enables them to interact with both water and oils, making them essential in various applications, including cosmetics, pharmaceuticals, and food processing.