Technically, all true soaps are lye soaps produced by the saponification of some form of fatty acids with either sodium and/or potassium hydroxide, either of which can be called lye. A variety of fatty acids can be used from either animal or vegetable sources.

In the early days of soapmaking, there were no good ways of measuring the exact quantities of fatty acids and lye being used, so in many cases, excess lye was added and the soap produced was highly alkaline. When used, the excess lye will saponify any fats with which it comes in contact. If you are trying to remove grease from clothing, the excess lye is ideal. If you are using the soap for shaving, the lye will gladly saponify the fats in your skin...ouch.


The first soaps were likely produced by someone roasting their meat over an open fire. Any fats dripping from the meat onto the ashes of the fire would produce soap. Somewhere along the way, someone realized that the soap had utility as a cleansing agent.

One of the earliest recorded instances of soap being produced commercially was jabón de Castilla. Although named after the Castile region of Spain, the origin of the soap appears to have been Aleppo, Syria where soap was made from laurel oil and soda ash, a crude form of sodium carbonate formed from the ashes of burned plants. Sodium carbonate is a weak form of lye. It is also called washing soda (in contrast to baking soda sodium bicarbonate) because it is good at removing grease from clothing.

In Spain, olive oil was more available than laurel oil, so today Castile soap is produced primarily from olive oil and lye. However, in some formulations, other vegetable oils are also used: laurel oil, coconut oil, etc. Since it does not contain tallow or other animal fats, Castile soap is classified as a vegan soap.

Unfortunately, as you probably know, olive oil does not produce the most stable shaving lather. However, in the interest of science, I have shaved with Castile soap. Compared to most shaving soaps, both traditional and modern, the lather is fairly slick, but cushion is lacking, so I would not want to shave regularly with Castile soap. However, I have also tried shaving with some tallow based bath soaps such as Yardley of London Cocoa Butter soap and find it to be as good or better than some inexpensive, traditional shaving soaps like Williams and Arko. Again. The cushion is not great, but the cocoa butter leaves a nice post shave feel. If I could not afford to purchase better quality shaving soaps, I would use Yardley.