Lye soap is an old fashioned type of hand made soap.
In the past, people couldn’t just go to the corner convenience store to get provisions. In fact, it wasn't until the last century or two that that it would be common for a town to have a general store. Until then, people had to make their own supplies, and that include soap.
They usually made soap out of lard and lye. The lard was collected around autumn, when they would kill the hogs. The lye, on the other hand, was processed from ashes, stored in a wooden bin kept next to the stove. During soap making season, they would pour water into this bin, then siphon off the resulting mixture.
They would then mix the lard and lye. The proportions had to be correct, because too much lye would burn the skin, while too little would lead to a gooey mess and the soap would simply fall apart. While there was no one “formula” but people believed that if an egg was placed in the mixture, it should sink just enough for the tip to float above the surface.
The next ingredient to lye soap was hours of hard work. People had to stir lard and lye in a pot propped on an open fire. They would do this until the soap hardened enough for the soap paddle to “stand straight” when left in the middle of the pot. They would then pour the mixture into pans, where it would be left to stand for two to four weeks. Lye soap was used for bathing, laundry, and general cleaning.
Today, despite the proliferation of different kinds of commercial cleansers, many people still prefer lye soap (especially since they don’t have to make it themselves). They believe that since it has no chemicals, it is gentler on the skin. It is also thought to heal insect bites. Modern lye soap use natural oils made from aloe, coconut or jojoba instead of lard.