For those unfamiliar with making soap, seeing lye, aka sodium hydroxide or potassium hydroxide as an ingredient in handmade soap can be a little scary. Today I thought I'd share why it's in there and why it's nothing to scare you away from handmade soap.
From the Wikipedia page on Saponification:
Saponification is the hydrolysis of an ester under basic conditions to form an alcohol and the salt of a carboxylic acid (carboxylates). Saponification is commonly used to refer to the reaction of a metallic alkali (base) with a fat or oil to form soap. Saponifiable substances are those that can be converted into soap. http://en.wikipedia.org/wiki/Saponification
The basic soapmaking process involves adding a solution of lye and water or some other liquid to oils. The lye reacts with the oils to make soap (saponification). Lye is necessary for saponification to occur and is therefore used in making all soap.
This site has a cool animated diagram showing the chemical reaction: http://waltonfeed.com/old/old/soap/soapchem.html
Assuming the maker’s calculations are correct, all of the lye reacts with the oil, thus leaving no trace of the lye in the final product. Because of this, you will often see terms such as “Saponified Coconut Oil” or “Sodium Cocoate”. Both terms refer to coconut oil that has reacted with lye to saponify.
Many soap makers, including myself, also take a small discount in the amount of lye used. This adds a cushion to further ensure that there are no traces of lye in the final product. It also produces a milder bar without sacrificing the cleaning properties of the soap.