Sodium Hydroxide
Production
Sodium hydroxide is made by electrolysis of brine, which also yields chlorine and hydrogen, or by reacting lime with soda ash.[1]
Why it is in cosmetics
As a pH adjuster, sodium hydroxide raises the pH of a formula that would otherwise be acidic. Most of its alkalinity is neutralised by the other ingredients, so little free hydroxide remains. Its caustic nature is therefore unlikely to show in typical finished products.[1] The EU cosmetic ingredient database (CosIng) lists its functions as buffering and denaturant.[2]
Depilatories and hair straighteners are the exception. In them it raises the pH to very high values, which enables or enhances their action. In 2015, sodium hydroxide was reported to the US Food and Drug Administration as used in 5,147 cosmetic formulations, about half of them leave-on skin care. It is also used in bath soaps and detergents, at up to 12.9%.[1]
Safety
Concentrated sodium hydroxide can cause severe burns. It can destroy skin tissue at once, and the higher the pH, the greater the damage. After contact, it must be removed quickly and completely. In skin irritation tests it was corrosive at concentrations as low as 1%. It can also rapidly penetrate the tissues of the eye.[1]
In 2016 the Cosmetic Ingredient Review (CIR) expert panel found sodium hydroxide safe in hair straighteners and depilatories used as recommended. Users of these products should minimise skin contact. In all other assessed uses it is safe when the product is formulated to be non-irritating.[1]
EU rules
The amount of sodium hydroxide in cosmetics is limited: in the EU, nail cuticle solvents may contain up to 5%, and hair straighteners up to 2%, or 4.5% for professional use. As a pH adjuster it is allowed up to pH 12.7 in depilatories and up to pH 11 in other products. Labels of cuticle solvents and hair straighteners must warn "Contains alkali", "Avoid contact with eyes", "Can cause blindness" and "Keep out of reach of children".[3]
Products containing it
- Energizing Face Cream, Eucalyptus Nun's Valley Madeira (I 140)
- Eye Contour Cream, Secret Of Serenity (I 406)
Sources
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 C. L. Burnett and B. Heldreth; Cosmetic Ingredient Review, Safety Assessment of Inorganic Hydroxides as Used in Cosmetics. Final report, 25 January 2016.
- ↑ European Commission, CosIng: SODIUM HYDROXIDE. Retrieved 9 November 2026.
- ↑ European Commission, CosIng, Annex III: list of substances which cosmetic products must not contain except subject to the restrictions laid down. Retrieved 9 November 2026.