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Sodium Hydroxide

The pH adjuster.

What it does

Balances the product's pH. In soap, it reacts with oils to make the soap itself.

Good to know

Very strong on its own, but it reacts with other ingredients and only a little is used. The EU limits it, for example to a pH of 11 or lower in most products.

Often found in: Shampoos, Shower gels, Sunscreens

Around the world

• United States: No FDA limit. The FDA doesn't approve cosmetic ingredients before sale. Source
• EU and UK: Limited by use: up to 5% in cuticle removers, 2% in home hair straighteners, and below pH 11 as a pH adjuster. Source
• Canada: Not on Health Canada's Hotlist of restricted ingredients. Source
• Australia: Controlled above 5%, or above pH 11.5 (Schedules 5 and 6). Below both, no limit. Source

Sources

• PubChem: Sodium hydroxide (Independent)
• CIR: Safety Assessment of Inorganic Hydroxides as Used in Cosmetics (2021) (Industry-funded)