Sodium Hydroxide

Sodium Hydroxide, also known as lye, is a very basic-whiter solid that is part of most cosmetic formulations. It principally works to adjust the pH of skincare products so that the latter is both effective and compatible with skin tissue. Examples include Sodium Hydroxide, which has an important role in maintaining the appropriate pH value of the products containing active ingredients such as AHA or BHA. All these kinds of exfoliants need a particular pH range to work effectively, and that can be provided by sodium hydroxide.
Sodium hydroxide has been in use for many centuries. Ancient Egyptians used lye to make soaps by the process of saponification, where fats and oils react with lye to form soap. The same basic process goes into the manufacture of modern-day soaps.
While pure sodium hydroxide is a seriously irritating compound to the skin, in cosmetic products its usage is very small in amount and quite controlled. Since it will react with other ingredients during formulation and get neutralized, the end product can be safely applied on the skin without causing irritation of any kind.
In all, sodium hydroxide is used to adjust the pH of products in skincare for ensuring the activity of ingredients. The fact that it has been used in soap-making for centuries just goes to show how ever-present it is in formulation even today.