Let me start off with saying: No Lye - No Soap.
It really is that simple.
I'm sure you've noticed by now, that soap doesn't exactly occur naturally. It doesn't grow on trees, and you can't dig it up. Soap first starts with a liquid and lye. Historically, Sodium Hydroxide - Lye, was created by treating Sodium Carbonate with Calcium Hydroxide in a metathesis reaction. Essentially, the sodium would bond to the hydroxide molecule resulting in a simple switch - creating Calcium Carbonate and Sodium Hydroxide, however modern methods utilize a chloralkali process. But here's the kick, per the FDA, without lye, you don't have a true soap. In fact, there's a name for that kind of "soap"... It's called a detergent.
Now, lye itself is dangerous, its an extremely caustic alkali that is used in tissue digestion, melting down metals, but also in food preparation (including softening the olives that we love to put on our salads and pizza). It's also used as an industrial cleaning agent - often simply called caustic soda. Interestingly enough, it has also been used for the blood detection of carbon monoxide poisoning - with blood samples turning a brilliant red (vermillion) color upon the addition of sodium hydroxide solution.
So why would you want it in your soap?
Well to understand that, we need to look a bit at history. The earliest known recipe for soap was from around 2800 B.C., written on ancient Babylonian pottery. It detailed a product made from the fats of animals, combined with wood ash and water which was used as a cleaning solvent for almost everything except the body. 500 or so years later, the Egyptians (and Syrians with their Aleppo Soap) would perfect it, and years later, the Romans would use it in their bath houses and to clean laundry in the rivers.
We as a species have been producing some form of soap for 5000 years.
Cut to the point.
Alright! Sorry, I like history... Once lye is added to a liquid (water, beer, milks, tea, coffee), it creates something called a lye solution. Hard stuff right? Well, once that lye solution is blended with oils, it begins a process called Saponification. This is where the actual chemical process of soap creation happens. Oils are composed of fat molecules called triglycerides. When tryglycerides meet the lye, they are both chemically transformed, creating soap and natural glycerin. Neither of the original ingredients exists anymore. All of the lye (sodium hydroxide for bar soap, potassium hydroxide for liquid soap) is converted in the process!
So while soap is made with lye, it doesn't actually contain any. Modern methods of measuring and calculating allow modern soap-makers to use proper oil to lye mixtures, ensuring that all of the lye is converted. Many soap-makers including Special Flower Oil Co take that a step further, using more oil than is necessary for the conversion lye in a process known as superfatting. Superfatting is literally extra fats left in the soap that don't become part of the soap. These become wonderful emollients that help to nourish the skin with additional benefits that only an oil can provide.
So what about my normal store bought bar of soap, it doesn't have Sodium Hydroxide or Lye listed in the ingredients.
Actually it does! If your normal bar of soap contains things like:
Sodium Palm Kernelate
Then you've just discovered lye in your soap! Those "sodium -ates" indicate an oil that has been mixed with sodium hydroxide, and "saponified oils" indicates that a certain group of oils and butters have been mixed with lye and a liquid.
This isn't necessarily made to deceive a customer. Natural soap-makers know that people are afraid of the word lye. We aren't going to treat you all like children. We feel that if you're looking at our hand-crafted small-batch soap, then you've probably got a good handle on what soap is.
But don't be fooled by "Lye Alternatives."
Some soap-makers try to make a posturing point, claiming to use lye alternatives - for example making a soap out of glycerin (melt and pour soap-makers, I'm looking at you), claiming that their soap doesn't have any lye involvement. Glycerin is a natural product of the saponification process.
Understanding some of the basic chemical processes can really go a long way to changing the public perception of lye. Lye isn't a bad thing. Sodium Hydroxide isn't scary (unless you messed up a beer/lye solution and it turns into a volcano, believe me... it's scary for that 2.3 seconds of "oh sh..."). In the hands of a good soap-maker, lye crafted with soap is superior in quality to those commercial detergents masquerading as soap. Frankly we love and respect lye. you should too.