Sodium Hydroxide

What it is

Although pure sodium hydroxide (commonly called lye or caustic soda) is an aggressive alkaline substance, in cosmetics it is added in minute amounts to neutralize acids and adjust product pH. As it reacts in the water phase, the alkali converts into neutral salts and water. The finished product contains these reacted components rather than free, unreacted lye.

What it does

• Adjusts pH. A formulator can use it to move a product toward its intended acidity or alkalinity.
• Neutralizes acids. When it reacts with an acid, the reaction helps form a salt and water rather than leaving all of the added alkali unchanged.
• Helps a formula work as designed. pH can affect texture, stability, preservation, and how certain ingredients behave. It is a supporting ingredient, not the reason to buy a product.

Who it suits

For shoppers, the important distinction is between concentrated raw sodium hydroxide and the finished product made with it. Seeing sodium hydroxide on an ingredient list does not mean the formula is caustic or that it will burn your skin. The ingredient list alone does not tell you the amount or finished pH. A well-formulated product is designed around its final properties, not just the starting materials.

If a product stings or feels uncomfortable, stop using it and consider the whole formula rather than assuming this pH adjuster is automatically the cause. People with persistent irritation or a skin condition should ask a dermatologist for guidance. There is no need to avoid an otherwise suitable product just because this technical name appears near the end of its ingredient list.

What to pair it with, and what not to

There is nothing to pair with sodium hydroxide: it is part of the product’s pH adjustment. Use the finished product as directed and do not try to change its pH at home. If you are using a separate acidic product, follow that product’s directions instead of attempting to neutralize it yourself.

Skin Realist check: A chemical name can sound dramatic without telling you much about the finished product. The formula is the thing you use, not a jar of raw ingredients.