Sodium Benzoate

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CAS No.: 532-32-1

Sodium Benzoate is the inactive salt of benzoic acid. It is soluble in water where it converts to benzoic acid, its active form, at a low pH. Benzoic acid is very pH dependent. While it shows some activity up to pH 6 (about 1.55%), it is most active at pH 3 (94%).

As benzoic acid, it is considered to be primarily an anti-fungal, but it shows some activity against bacteria.  It is poor against pseudomonads.  Benzoic acid is inactivated by non-ionics and by raising the pH.

Sodium Benzoate is not a broad spectrum preservative for cosmetic use and should be combined with other preservatives. If Sodium Benzoate is used as a preservative, the pH of the finished product may need to be lowered enough to release the free acid for useful activity. 

Sodium Benzoate is often combined with Potassium Sorbate in low pH products to provide a synergistic preservative effect against yeast and mold.

Following is a chart of the relative activity at various pH:

Activity of Benzoic Acid
pH % Active Benzoic Acid
3 94
4 61
5 13.7
6 1.55
7 0


There is some concern that Sodium Benzoate in combination with L-Ascorbic Acid in products can form Benzene, a known human carcinogen. The presence of ascorbic acid and benzoates alone does not lead to the formation of benzene.  Certain additional conditions are required for trace levels of benzene to form, including heat, ultraviolet light and metallic ions in the mixture. Therefore, a product containing ascorbic acid and benzoates will not necessarily contain any detectable levels of benzene.  The use of EDTA, which chelates metallic ions can therefore be of assistance in the inhibition of benzene formation.    Citric Acid is not thought to induce significant benzene production in combination with Benzoic Acid, but some evidence suggests that in the presence of ascorbic acid and benzoic acid, citric acid may accelerate the production of benzene.  Therefore, the use of Sodium Benzoate and L-Ascorbic Acid and Citric Acid in the same cosmetic formulations should be avoided. 

All cosmetic products should undergo microbial testing to ensure the efficacy of any preservative system.

INCI: Sodium Benzoate

California Prop 65 Statement: The following statement is made in order to comply with the California Safe Drinking Water and Toxic Enforcement Act of 1986. This product is not known to the State of California to cause cancer, birth defects or other reproductive harm.

Recommended Use Levels: Up to 1%
Solubility: Soluble in water up to 55%

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