You may have probably noticed that lye (known as sodium hydroxide or potassium hydroxide) is one of the essential ingredients of soap. On its own, lye is a dangerous alkali which can burn your skin and cause damage to your lungs if inhaled. But once it's mixed safely and properly with oils at a certain temperature, a chemical reaction occurs that saponifies the fats in those oils, thus creating natural soap!
Once the soap has cured, there is NO lye left at all and the soap is gentle and moisturizing.
Conventional lye was obtained by leaching ashes, containing largely potassium carbonate or "potash". It was the traditional way for soap makers to get the alkali in old days.
Any “beauty bars or bath bars” you may find without lye is not soap at all, but a detergent that strips the skin of moisture.
You cannot make real soap without lye!