Sodium Benzoate
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The sodium salt of benzoic acid, a compound found naturally in low levels in cranberries, plums, and some other fruits, but produced synthetically for commercial use.
Why it’s used
It is a preservative, added to stop mold, yeast, and some bacteria from growing in water-based products, protecting both the formula and the person using it. It works best in slightly acidic formulas, which is why it is often paired with citric acid or another mild acid.
What the evidence says
Sodium benzoate has a long history of use in both food and cosmetics and is reviewed as safe by the Cosmetic Ingredient Review and permitted as a food additive by the FDA at regulated levels. A known chemical interaction is that it can react with ascorbic acid (vitamin C) in the presence of heat or light to form small amounts of benzene, a concern addressed by reformulating products to avoid combining the two, or by adding chelating agents to limit the reaction.
Context
Used at low percentages, generally under 1 percent, in both rinse-off and leave-on products. The benzene-formation concern is specific to formulas combining it with ascorbic acid under heat or UV exposure, not a general property of the ingredient on its own.
Educational information, not medical or safety advice. Consult a professional for allergies or medical concerns.