Does soap contain Sodium Hydroxide (caustic soda or lye)?
The truth about soap - No Lye!
As an artisan soap maker, I spend quite some time talking about soap. Secretly, I love it and will never get bored of talking about it. I get so much great feedback from people who use my soap and tell me how gentle it is and how it is the best thing they have ever used for their... (fill the blank with your most unwanted skin condition). But now and then I have someone tell me they have been told not to use soap because "it is made with caustic soda!"
Before we get started with the details, or for those with a short attention span for chemistry, here are the FACTS spelt out in plain English for you to commit to memory:
1. You need caustic soda to make soap.
2. No caustic soda remains in the soap once it is made.
For those who don't care for soap because they love their "non-soap" body wash, keep an eye out for my next article titled 'Why does my "natural" body wash contain petroleum derivatives'?
So what is Caustic soda?
Chemically known as Sodium Hydroxide (NaOH), Caustic soda is traditionally known by the common name Lye. It is a very simple molecule that is made by reacting salt water with electricity. It has the common name of caustic soda due to the fact it is alkaline/caustic (opposite of acidic) and it is part soda (sodium).
Turning oil into soap
In simple terms, making soap involves neutralising oil (in our case Coconut oil & Olive oil), which is acidic, with an alkali such as Sodium Hydroxide. It is often a surprise for people to learn that oil is acidic. Have you ever heard the term 'fatty acids'?
What happens to the lye?
At the end of the soap making process, all the lye has been consumed and only soap and glycerine remain. To guarantee that 100% of the lye is consumed, we put more oil into the soap than the lye can consume; we call this superfatting. Because there is an excess of oil, if made correctly, no lye can remain in super-fatted soap. It is the superfatting in UltraNaturals soap that helps make it so gentle.
The key message to take away: Caustic soda is used to make soap but does not remain in the soap.