A Brief and Simple Chemistry Lesson in Soap Composition

All these years, I have been using and recommending soap, but I’ve only had a vague notion of its chemical composition and how it works. I decided to do some research into the topic of soap composition so that I could better explain to patients what it does.

I found out that soap is made by adding sodium hydroxide (lye dissolved in water) to animal or vegetable fats. As a result, there is a chemical reaction called saponification. Fatty acids release from the oily and fatty structure, binding with the sodium. The resulting fatty acid salt is soap as we know it.

Soap composition is just the first part; the second and equally important aspect is how it cleans. When soap cleans, a complex chemical process ensues. When water and soap “mix”, the sodium component is water soluble, but its fatty acid component is hydrophobic and will not dissolve in water. This property of soaps creates a structure called a micelle, which is essentially a cell-like structure with a soap membrane. You can see this phenomenon at work when you add soap to a greasy pan with water in it. These micelles bind dirt, oil and grease which we can then wash off with warm water. This is the essence of the cleaning process.