preservative
Sodium Benzoate
A widely used preservative in aqueous cosmetics and food. Effective against bacteria and yeast at acidic pH. Works synergistically with potassium sorbate for COSMOS-compatible broad-spectrum preservation.
Benefits
- Broad-spectrum antimicrobial at pH <5.5
- COSMOS-certified preservative option
- Food-grade safety record
- Synergistic with potassium sorbate
- Effective against gram-negative bacteria at low pH
Example uses
- Brightening serums (avoid with high-concentration L-ascorbic acid without metal chelation)
- Natural certified skin care
- K-beauty toners
- Aqueous serums
- Botanical mists
Mechanism of action
Undissociated benzoic acid (the active form below pKa 4.2) inhibits key microbial enzyme systems by reducing intracellular pH via proton ionophore mechanism, disrupting the proton gradient essential for microbial ATP synthesis. At higher pH, the dissociated sodium benzoate ion has substantially reduced antimicrobial efficacy.
Clinical evidence · High
Extensively characterised safety and efficacy profile. GRAS food status. Multiple SCCS cosmetic assessments.
Effective concentration range
0.1–0.5%
Formulation notes
Most effective below pH 5.5. Above pH 6, the benzoate anion (less active form) predominates. Requires potassium sorbate pairing for full spectrum in COSMOS-compliant formulations. Incompatible with formulations using iron or heavy metal co-ingredients (benzoate chelation).
Watchouts
Reacts with ascorbic acid (vitamin C) in the presence of transition metals to form benzene — a carcinogen. This reaction is concentration and condition-dependent and rarely clinically relevant in cosmetics at typical use levels, but formulations combining sodium benzoate and vitamin C should minimise transition metal co-contamination.
Conflicts with
Controversies & overclaims
The sodium benzoate + ascorbic acid + transition metal benzene formation reaction is a food safety concern that has been applied to cosmetics. At cosmetic use concentrations and without transition metal contamination, the reaction is de minimis in finished products.
Market positioning
Sold as natural-compatible preservative. Accurate within its pH range. The benzene formation with vitamin C is a formulation concern, not a typical safety risk in well-formulated products.
Comedogenicity
0 / 5
Sensitisation risk
Low
INCI & aliases
Sodium Benzoate
benzoic acid sodium salt · E211 · benzoate
Clean beauty perception
Accepted in natural and COSMOS-certified formulations. EWG rating 1. One of the most widely used natural-compatible preservatives.
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