The effectiveness of soaps as cleaning agents lies in their dual hydrophobic-polar structure. In the bulk of the liquid, soap molecules remove their hydrocarbon tails form the water by forming spherical droplets or micelles, with hydrocarbon chains pointing to the interior and negatively charged heads on the surface (see right). Particles of grease, oil, and other hydrocarbons can be picked up and incorporated into the interior of the soap micelles, where the particles are isolated from the water environment. The grease-laden soap micelles then can be flushed away with water, with their negative surface charges helping to keep them apart.

Natural soaps are sodium or potassium salts of fatty acids, which are combinations of hydrocarbon and carboxyl groups. Other molecules can be manufactured that are combinations of hydrocarbon and sulfate or some other negatively charged group. These artificial detergents have many of the same properties as soaps, and we will discuss them in the next section.