Sodium Hydroxide is used as a pH adjuster in cosmetics. It is a strong base, meaning its pH is well above neutral pH 7. It may sound intimidating, but in truth it’s functioning to make products safer.
Overly acidic formulas with a very low pH can be extremely harsh on the skin. For example, alpha hydroxy acid formulations without proper pH adjustment can be dangerous and even cause chemical burns. Sodium Hydroxide efficiently corrects pH to the optimal level balancing intensity and efficacy for optimal results.
The chemistry of pH adjustment
Did you know, there isn’t actually sodium hydroxide in the finished formula we put on our skin? When we add sodium hydroxide to an acidic formula to adjust pH “it breaks up (dissociates) into sodium ions (Na+) and hydroxide ions (OH–).”1 We know sodium as plain old salt, which isn’t scary at all. The hydroxide ions are the things doing the actual pH adjusting—”they neutralize the hydrogen ions and turn them into water, raising the pH of the product.”1
So, when we pH adjust an acidic product with sodium hydroxide, we end up with a bit of salt, a bit of extra water, and perfectly optimized product pH.1 This is why sodium hydroxide is a safe and incredibly useful ingredient for cosmetic formulation.
 Wong, M. Is Sodium Hydroxide Safe in Beauty Products? | Lab Muffin Beauty Science. Retrieved 17 September 2022, from https://labmuffin.com/is-sodium-hydroxide-safe-in-beauty-products/