What it is
Potassium hydroxide (KOH) is a white, highly alkaline inorganic solid classified as a strong base. In cosmetic formulas it is used at low levels to set the pH of the finished product and to neutralize acidic ingredients, a role similar to that of sodium hydroxide. When it reacts with fatty acids it drives saponification, the reaction that forms soap, producing softer potassium soaps compared with the harder soaps made using sodium hydroxide.
Safety & warnings
In its raw, concentrated form potassium hydroxide is strongly corrosive and can cause serious burns to skin and eyes, and irritation of the respiratory tract from dust or mist. In finished cosmetics it functions only as a pH adjuster and is present in very small amounts; once the formula's pH is balanced, the remaining material exists as neutralized potassium salts rather than free caustic alkali, so the irritation risk of the final product is governed by its overall pH rather than the starting strength of the base.
Origin & sourcing
Potassium hydroxide is a synthetic, manufactured chemical. Historically it was produced by treating potassium carbonate (potash) with calcium hydroxide. It is now made primarily by the chloralkali process, the electrolysis of potassium chloride solutions, which also generates hydrogen and chlorine gases as byproducts.
History
Potassium hydroxide has long been associated with potash, the alkaline material obtained from plant ashes. The element potassium itself was first isolated by Humphry Davy in 1807 through the electrolysis of molten potassium hydroxide. Modern industrial production shifted to electrolysis of potassium chloride solutions.
Questions everyone asks
Is potassium hydroxide dangerous in my sunscreen?
In concentrated form it is corrosive, but in a finished sunscreen it is used in tiny amounts only to balance the formula's pH, so the remaining material is largely neutralized salts.
What does potassium hydroxide do in a formula?
It acts as a pH adjuster and neutralizing agent, helping bring the product to the intended acidity or alkalinity and neutralizing acidic ingredients.
How is it different from sodium hydroxide?
Both are strong bases used to adjust pH. Potassium hydroxide forms softer soaps in saponification, while sodium hydroxide forms harder ones.