Sometimes I have enquiries about why I use sodium hydroxide (or caustic soda) in my soaps. It is indeed a troubling thought for many due to the fact that it is such a corrosive substance! Often associated with its cleaning and stripping properties (think of greasy ovens, bbqs, paint strippers to name a few), it is difficult to fathom how this chemical has to wind up in soaps, especially handmade artisanal ones.
So, to allay any concerns, here is a simple (I hope) chemistry and history lesson.
“Soap” comes from the word saponification. It is essentially what you get when you mix alkali (NaOh or sodium hydroxide or caustic soda) with acid (oil). (When I use the word “acid”, think of the chemistry term and not “sour”.) Simply put, there can be no bar of natural soap without the caustic soda or sodium hydroxide.
The process of the caustic soda and oil mixing together in the right quantities gives you a neutral product which is the soap that we can safely use on our bodies without any damage to ourselves or the environment. So, we need to remember that the wonderful chemical reaction of the two main ingredients (caustic soda & oil) nullifies the corrosive nature of the caustic soda. In fact, during this process you even end up with a valuable substance called “glycerine” which adds to the moisturising properties of a natural handmade soap. (This glycerine is often extracted in commercial soap-making for other cosmetic uses and in its place, cheaper chemicals added.)
In days of old, some people would have discovered that when ash (an alkaline caustic substance) was mixed with animal fats (acid) – dirt and oil could be removed a lot easily from clothes and cooking utensils (still practiced amongst poor village communities around the world).
Taking a cue from this, some people made a solution of water and ash (lye – this term is still used by some soap-makers today to mean a caustic soda and water solution) to produce an alkaline solution and mixed it with lard or other fats and oils to make soap.
I tried this method in my early days of soap-making and quest for self-sufficiency. That was nearly 17 years ago, when I was also happy to save up any cooking oil remnants for my soap projects. The inexact science of it all did not suit me. In the end, I was grateful to access the resources available to me in the form of pure caustic soda crystals (99.8%) instead of concentrated ash water which I couldn’t efficiently use. I also allowed myself the luxury of using other local and exotic oils – a practice that I am happy to continue to this day.
To conclude, let me say that a good soap-maker always uses recipes for soap that have good cleansing properties without causing dryness of the skin (something that commercial soaps often do). A natural soap has to have the two basic ingredients – caustic soda & oils. This is often combined with other natural ingredients in the form of essential oils, botanicals and mineral clays to give you a product that is gentle and caring on the skin.