Amongst the many scientific names of chemicals on commercial soap labels it's hard to notice sodium hydroxide as an ingredient. When reading the few ingredients on handmade soap, it's easy to spot. Handmade soap usually advertises their use of natural ingredients, but there is always the question of what is sodium hydroxide and is it necessary in soap? So let's dig deeper into the use of sodium hydroxide in soap.
Sodium hydroxide is a caustic soda that when combined with animal fat or vegetable oil, processes into soap. This process is called saponification. Lye is necessary to make bar soap, just as potassium hydroxide is needed for liquid soap. Essentially, soap is a mixture of base oils, a diluted lye solution, and herbal additives.
During the soap making process the lye is heavily diluted with water, and added to the oils to create a thick mixture. The mixture is then added to a mold for 24 hours to harden, and set to cure for 4-6 weeks. During the curing process, the soap bars lose water weight, in which the sodium hydroxide is dissolved. Therefore lye is needed for the chemical process that soap goes through, but it's not present in the final product.
Many of our parents & grandparents are very familiar with lye soap. It's what they remember as a harsh soap often mixed with animal fat. Back then the soap was harsh, but today we don't experience that due to advances in the curing process. Lye has been recorded and depicted in the transcripts of many ancient societies such as the Mesopotamia and Egypt. In modern times, soap makers generally use a synthetic sodium hydroxide discovered by Humphrey Day. The discovery of this alkali, made it easier and feasible for soap makers to enhance the traditional practice of making lye.
When dealing with lye it is very important to take the proper precautions, as it is very caustic and can irritate the skin directly. When making soap, I have to use goggles and gloves. I've gotten lye on my skin and in my eyes and it's not a good feeling whatsoever. If if comes in contact with the skin use an acid like vinegar to neutralize, and water for the eyes.