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Potassium Hydroxide

Well toleratedpH adjusterph-adjusterneutraliser

No meaningful concern for most people; irritation is possible but rare.

Also written as: KOH · Caustic Potash

What it is

Potassium hydroxide is the potassium counterpart of sodium hydroxide and does the same job: it is added in fractions of a per cent to lift pH or to neutralise acidic thickeners such as carbomer into a gel. Like sodium hydroxide it reacts and is used up, so the finished mask contains neutral potassium salts rather than free alkali.

What it does well

  • Brings a formula to skin-compatible pH and activates gelling polymers

    It is chosen over sodium hydroxide mainly for solubility and feel reasons; the finished pH, not the neutraliser used, is what matters for skin.

    Strong evidence

Worth knowing

  • Corrosive as a raw material, but not as used in a finished mask

    EU rules cap general pH-adjusting use at pH 11 and set specific limits for hair straighteners, cuticle solvents and depilatories, where high concentrations really can burn. A face mask at mildly acidic pH is not a caustic exposure.

    Matters most toUsers of hair relaxers and depilatory creams rather than mask users.

Where the EU stands

Concentration-restricted

Annex III entry 15a covers potassium and sodium hydroxide: 5% max in nail cuticle solvents, 2% general-use and 4.5% professional hair straighteners, up to pH 12.7 as a pH adjuster in depilatories, and up to pH 11 for all other pH-adjusting uses.

Regulation (EC) No 1223/2009, Annex III entry 15a · source ↗

Masks that contain Potassium Hydroxide