The cleansing activity of soap is determined by emulsification and micelle production. The basic combination of soap contains sodium and potassium salts of long-chain fatty acids (R-COO-Na+). The sodium ion is connected to the polar end of the molecule, whereas the alkyl part is the non-polar end. A soap molecule has both polar and non-polar components, i.e. hydrophilic and hydrophobic, respectively.
When dirt-laden water is mixed with soap, the soap molecules surround the dirt particles in such a way that the dirt molecule and the hydrophobic part become linked, while the hydrophilic sections point away from the dirt molecule. As a result, the non-polar group dissolves in the dirt particle, whereas the polar group does not. Because these micelles are negatively charged and do not coalesce, a stable emulsion is created.