Lye Worst Irritante No known benefits Lye description Also known as potassium hydroxide, this highly alkaline ingredient is used in small amounts in cosmetics to modulate the pH of a product. It’s also used as a cleansing agent, most often in pure soaps or soap hybrid products. In higher concentrations, lye can aggravate skin, even if used in rinse-off products. Related ingredients: Potassium Hydroxide Sodium Hydroxide