Sodium Hydroxide
Reviewed by Daisy · Last updated 18 Aug 2026
Also known as: lye
Highly alkaline ingredient | Used in small amounts in cosmetics (such as in exfoliants and cleansers) to adjust pH
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EWG Safety Score
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What Is Sodium Hydroxide?
Sodium hydroxide, also known as lye, is a highly alkaline (also known as “basic”) ingredient used in small amounts in cosmetics to adjust the pH of a product in a formula. This is seen particularly in products such as cleansers and in leave-on exfoliants, where the product’s pH needs to be held within a very specific range for maximum efficacy (between 3-4 is ideal for acid-based exfoliants, while cleansers are generally pH 4.5-6). Pure sodium hydroxide’s pH level is 13, but in cosmetics, it is only used up to pH 11.
Sodium hydroxide is seen in many applications in beauty products, such as nail cuticle solvents and hair straighteners, where it’s used in greater amounts (between 2% and 5% concentrations by weight) than in leave-on skin care products or makeup (for example, some lipsticks contain 0.25% sodium hydroxide). It’s also used as a cleansing and denaturing agent. It’s a significant skin sensitizer in concentrations of 10% or greater.
Clinical Evidence & References
Published Research
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International Journal of Trichology, January-March 2015, pages 2-15 [URL not available]
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Journal of Cosmetic Dermatology, September 2010, Volume 9, Issue 3, pages 174-184 [URL not available]
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Acta dermato-venereologica, March 1995, pages 97-101 [URL not available]
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http://www.cosmeticsinfo.org/ingredient/sodium-hydroxide [http://www.cosmeticsinfo.org/ingredient/sodium-hydroxide]
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https://www.cir-safety.org/sites/default/files/inorganic%20hydroxides.pdf [https://www.cir-safety.org/sites/default/files/inorganic%20hydroxides.pdf]
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Sodium Citrate
Is a salt of citric acid, which can be derived from citrus | Is primarily used to control the pH level of a product
Sodium Gluceptate
A chelating agent that helps stabilise formulations and reduce the impact of mineral impurities
Sodium Gluconate
The synthetic salt form of gluconic acid | Helps improve the stability of skin care formulas
Sodium Lactate
The sodium salt of lactic acid | Works as a hydration-enhancing ingredient due to its hygroscopic nature
Sodium Metaphosphate
A buffering agent that stabilises formulations and supports oral care products
Sodium Phytate
Synthetic salt form of the antioxidant phytic acid | Works as a chelating agent, keeping metals from binding to water in cosmetics
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