What exactly is soap?
Soap is the product of a chemical reaction that occurs between lye water and some sort of fat. That chemical reaction that subsequently takes place is called saponification. This is the same as the lye soap that all of our ancestors used. Lye is nasty stuff, it can eat right through your skin. The key to making good soap is to balance the chemical reaction properly so that all of the lye molecules have reacted with the oil and there is no more lye left in the finished product. Our ancestors may have had trouble balancing this equation because the lye would vary from batch to batch. If the ratio was off the soap might be soft and goopy, or it could be harsh and irritating to your skin.