Sodium hydroxide

Sodium hydroxide, also known as lye or caustic soda, is an inorganic chemical compound produced synthetically through the electrolysis of sodium chloride. Today, it is manufactured using modern brine electrolysis, in which it is formed as a by-product of chlorine production. This strongly alkaline compound has the formula NaOH and consists of sodium ions and hydroxide anions, which are responsible for its pronounced alkaline properties.

In cosmetics, sodium hydroxide acts primarily as a pH regulator and buffering agent. Its main role is to neutralise excess acidity in products, ensuring that the finished product is balanced and safe for the skin. In chemical peels and exfoliating products, it helps break down the outer layers of the skin, allowing dead skin cells to be removed. Sodium hydroxide is also used in soap-making, where it combines with vegetable oils and fats to form the basis of bar soaps through a process called saponification. In cosmetics, it is used at very low concentrations – approximately 2 % in hair relaxers, 4,5 % in professional hair relaxers and up to pH 12,7 in hair removal products.

Sodium hydroxide is particularly recommended in products designed to care for sensitive and mature skin, where precise pH adjustment is important. It is found in shampoos, shower gels, creams, soaps and even hair removal products. People with very sensitive skin, eczema or a compromised skin barrier are advised to consult a dermatologist before use, as sodium hydroxide in its pure form is a highly corrosive substance that causes severe burns.

Most high-quality cosmetic products containing sodium hydroxide are formulated within a safe pH range of 4,5 to 5,5, which corresponds to the natural pH of human skin. These products are usually well tolerated by the skin, provided the concentration is appropriate and they are used correctly according to the instructions. In the event of a chemical burn, the affected area should be rinsed immediately with cold water and neutralised with diluted vinegar or citric acid.