Why Soap Cleans

Man's Conquest of Substances:
The natural oil of the skin catches and retains dust and dirt, and makes a greasy film over the body. This cannot be removed by water alone, but if soap is used and a generous lather is applied to the skin, the dirt is "cut" and passes from the body into the water. Soap affects a grease film and water very much as the white of an egg affects oil and water. These two liquids alone do not mix, the oil remaining separate on the surface of the water; but if a small quantity of white of egg is added, an emulsion is formed, the oil separating into minute droplets which spread through the water. In the same way, soap acts on a grease film, separating it into minute droplets which leave the skin and spread through the water, carrying with them the dust and dirt particles. The warmer the water, the better will be the emulsion, and hence the more effective the removal of dirt and grease. This explanation holds true for the removal of grease from any surface, whether of the body, clothing, furniture, or dishes.