What Is Sodium Hydroxide Doing in Cosmetics?
Arin Editorial · how this is made
Seeing 'sodium hydroxide' on a label might make you think of drain cleaner. The same chemical really is in creams, shampoos, and soaps. But that doesn't mean it acts like a drain cleaner on your skin. A few sentences are enough to understand what it does.
What is this substance?
Sodium hydroxide is also known as caustic soda or lye. In its pure form it is a white solid that forms a strong alkaline solution in water. For this reason, industry uses it in everything from drain cleaners to paper production. It's used in cosmetics too, but the amount and purpose are very different.
What does it do in cosmetics?
Its main job is pH adjustment. Skin's natural pH is between 4.5 and 5.5, and formulas should stay close to that range; sodium hydroxide brings acidic mixes to the desired level. Its second key role is saponification: it reacts with fats to make soap. It also works as a denaturant in some alcohol-based products.
Is it harmful?
Pure sodium hydroxide is corrosive. It is classified as a burn and damage hazard for skin and eyes. Those classifications describe the danger of the concentrated chemical. The amount used in cosmetics is tiny, just enough to balance pH. In the EU, after an SCCS assessment, this substance is listed in Annex III of the Cosmetics Regulation with approved restricted use. Genetic damage tests give conflicting results: some found an effect, some didn't. So no firm conclusion emerges. For skin sensitization, it is recorded as 'not classified'.
What about the drain cleaner comparison?
Most people get uneasy when they see it in cosmetics because of the drain cleaner comparison. That comparison isn't wrong, but it's incomplete. A substance's hazard depends on its concentration and route of exposure. Concentrated lye burns skin; a low-concentration solution mostly just adjusts pH. The final concentration in a product is what determines safety.
Are there alternatives?
Formulators can also use amino acids like arginine and lysine for pH adjustment. These ingredients balance pH while providing care benefits. Still, sodium hydroxide remains a cheap and effective option.
Under EU cosmetics regulation, it is approved with restrictions and listed in Annex III after SCCS assessment.
If you see sodium hydroxide on a label, don't panic. It means the product's pH has been moved to a skin-friendly range. You'll find it more often in exfoliating masks or soaps. If your skin is sensitive, test the product on a small area first.