What it is
Sodium benzoate is the sodium salt of benzoic acid, a white crystalline powder used as a preservative. In cosmetics it helps products stay stable and resist spoilage and works mainly against fungi. Its activity is pH-dependent and is best at acidic pH levels of roughly 3 to 5, where it converts to benzoic acid and lowers microbial intracellular pH; because it is relatively weak on its own, it is commonly paired with other preservatives such as potassium sorbate.
Safety & warnings
Sodium benzoate is a widely used and generally well-tolerated preservative at the low levels typical of cosmetics. The benzene-formation concern is specific to beverages where it coexists with ascorbic acid and is accelerated by heat and light; it is a food-chemistry issue rather than a routine topical one. Because it is most effective in acidic formulas, it is usually combined with other preservatives to give adequate protection.
Origin & sourcing
Sodium benzoate is manufactured by neutralizing benzoic acid with sodium hydroxide. The benzoic acid used is itself produced commercially by oxidizing toluene with oxygen, making the finished ingredient a synthetic compound.
History
Sodium benzoate and benzoic acid have a long record as food and product preservatives. A notable safety episode arose in beverages: sodium benzoate combined with ascorbic acid (vitamin C) can form trace benzene, and 2006 FDA testing found a small number of drinks exceeding benzene limits, prompting reformulations.
Questions everyone asks
Is sodium benzoate safe in skincare?
It is a common, generally well-tolerated preservative at the small amounts used in cosmetics; the benzene concern relates to vitamin C beverages, not typical topical products.
What does sodium benzoate do?
It acts as a preservative, helping products last longer by working against microbes, mainly fungi, in acidic formulas.
Why is it combined with other preservatives?
On its own it is relatively weak and works best at acidic pH, so it is often paired with ingredients like potassium sorbate for broader protection.