Ingredient
Sodium Hydroxide
Caustic Soda
Lye
What it is
A strong alkali used in tiny amounts as a pH adjuster to neutralize acidic formulas like this azelaic acid serum, not as a standalone active.
How it works
It donates hydroxide ions that neutralize free carboxylic acid groups (e.g. from azelaic acid), raising the formula's pH into a comfortable, skin-compatible range.
What it does
Buffering
Concerns to know
-
Well tolerated
No significant safety concern is reported for this ingredient as used in cosmetics.