There are several ways to make soap, but traditional, made-from-scratch soap is made by mixing animal or vegetable oil, water and lye, a process known as saponification.
Many soaps include added fragrance, colors, essential oils and other ingredients, although they are not necessary components in a typical bar of soap.
Lye is an extremely caustic, alkaline, chemical solution used in many cleaning products. The amount of lye used to make soap depends on the type of oil that is being used.
When mixed with water, solid lye dissolves and the water heats up. Lye is an extremely dangerous material to work with because it's so abrasive. It can cause severe burns, even if it only comes in contact with skin for a couple of seconds.
There are two types of oils used to make soap: vegetable and non-vegetable (animal).