Sodium Hydroxide

What it is

Sodium hydroxide is a strong inorganic base, familiar as lye or caustic soda, supplied to factories as a concentrated solution that is genuinely corrosive to handle. In a face mask it is used at a fraction of a per cent to raise pH, and above all to neutralise acidic gelling polymers such as carbomer so they swell into a clear gel. In that reaction the hydroxide is consumed: what remains in the finished product is the neutral sodium salt of the polymer or acid, plus water. This is why a finished cream at pH 5 is not a caustic exposure, even though sodium hydroxide is listed on the pack.

What it does well

• Brings the finished product to a skin-compatible pH

  Many raw materials are strongly acidic on their own. Adding a measured amount of sodium hydroxide is the standard way to land the finished mask near skin's own pH of roughly 4.5-5.5, which supports barrier function and preservative performance.

  Strong evidence

• Turns acidic thickeners into stable, clear gels

  Carbomer and similar polyacrylic acid polymers only build viscosity once neutralised. Sodium hydroxide is the most common neutraliser, and the gel texture of a great many masks depends on it.

  Strong evidence

Worth knowing

• The popular fear that 'lye in your cream' burns skin is misplaced

  Concentrated sodium hydroxide is corrosive, but in a finished cosmetic it has already reacted and only the resulting neutral salts remain; EU rules cap general pH-adjusting use at pH 11 and legally require every finished product to be safe as sold. A well-made mask sits at mildly acidic to neutral pH.

  Matters most toNobody, for normal face masks. Reading it as a warning sign on an ingredient list is a misunderstanding.

• Deliberately alkaline products are a different matter

  Where sodium or potassium hydroxide is used at high concentration for its alkalinity, such as hair straighteners (up to 4.5% professional) or depilatories at up to pH 12.7, chemical irritation and burns are real risks and the EU restricts those uses specifically. Face masks do not fall in this category.

  Matters most toPeople using hair relaxers, cuticle removers or depilatory creams, not mask users.

Where the EU stands

Sources (2)

Every link goes to the original: a journal, a PubMed record or an EU document.

1. [1]
   Skin pH: from basic science to basic skin care

   Acta Dermato-Venereologica · 2013 · doi:10.2340/00015555-1531

   Maintaining skin's acidic surface pH matters for barrier repair and antimicrobial defence, which is precisely why formulators adjust pH rather than leaving a product alkaline.

2. [2]
   The pH of commercially available rinse-off products in Sri Lanka and their effect on skin pH

   Ceylon Medical Journal · 2007

   Alkaline soaps raised skin surface pH and recovery back to baseline was slower than with pH-balanced products, supporting the practice of adjusting finished cosmetics to a mildly acidic pH.