The Beauty of Sodium Benzoate

Dear Valerie: I’ve been getting a bit of pushback from our product development team about using sodium benzoate as a preservative. Sometimes I’m not even intentionally adding it—it’s a sub-preservative of a raw material I added to the formula. I don’t understand why sodium benzoate is getting all the hate lately, can you please shed some light?

— Notta Hater

Dear Notta:

I’ve heard some of the same feedback as of late, and truth be told, I’m unsure. Usually when an ingredient jumps on the hate train, it’s because the EWG or an ingredient-checker app have deemed it to be unsafe. After begrudgingly reviewing the EWG score (not for accuracy, for this column!), I see sodium benzoate is rated a 1-2* (*depending on usage), which is considered low risk. EWG does rate the risk higher (which presumably would increase the 1-2 rating) if sodium benzoate is used in powder formulations, due to the increased risk of inhalation.

While there seems to be anti-preservation sentiment, or at least, anti-synthetic preservation, I don’t think sodium benzoate has fallen victim to this trend. Even natural or “clean” brands are OK with sodium benzoate, although there is often an air of contention when agreeing this preservative meets their approved lists—they ask, “It’s at least an organic acid, right?” To which, I smile and nod.

Sodium benzoate has recognized GRAS status, meaning it’s generally recognized as safe, even for consumption. We can thank Dr. Harvey Wiley, a government chemist, for his work in the early 20th Century to establish this, which also led to the creation of the US Food and Drug Administration. (If you haven’t read The Poison Squad by Deborah Blum, I highly recommend it!) Sodium benzoate also has low dermal toxicity, and when ingested, is rapidly metabolized. It’s approved for use in cosmetics in nearly every regulatory geography. What gives?

The only thing I can think of is benzene.

Thanks to Valisure and their unsure methodologies (according to the FDA), consumers are more concerned than ever about benzene lurking in their products. Benzene is not intentionally added, but rather is an impurity found in raw materials that have origins in benzene chemistry, such as carbomers polymerized in benzene and aerosol propellants. Benzene is an established carcinogen, and has strict limits set forth by the FDA and other global regulatory bodies. In the US (and now, China), for example, the limit is two parts per million and has to be unintentionally added and unavoidable.

How is this related to sodium benzoate? Aside from sounding similar, which may trigger chemophobia in the chemical illiterate, benzoic acid, the free acid form of sodium benzoate, can undergo a decarboxylation to form benzene under specific conditions, such as when used in combination with ascorbic acid and erythorbic acid, exposure to elevated temperatures, light and metals.¹

It’s important to note this reaction doesn’t happen with ease—specific conditions must be present. Ascorbic acid must first generate hydrogen peroxide in the presence of a transition metal such as copper or iron. Hydrogen peroxide will generate free radicals using the transition metal. These free radicals can then decarboxylate sodium benzoate, generating benzene. Using a chelating agent reduces the propensity of any residual transition metals in your other raw materials to generate this reaction cascade with ascorbic acid. (In soft drinks, the presence of sugar mitigates this cascade.)

Bottom line, there is no need to formulate your products without sodium benzoate just yet. You can, out of an extreme abundance of caution, avoid scenarios in which sodium benzoate can react, test your finished products for benzene or have a toxicologist review any formulas of concern.

References:

1. Gardner, Lalita K., Glen D. Lawrence. “Benzene production from decarboxylation of benzoic acid in the presence of ascorbic acid and a transition-metal catalyst.” Journal of Agricultural and Food Chemistry 41.5 (1993): 693-695.

Valerie George is a cosmetic chemist, science communicator, educator, leader, and avid proponent of transparency in the beauty industry. She works on the latest research in hair color and hair care at her company, Simply Formulas, and is the co-host of The Beauty Brains podcast. You can find her on Instagram at @cosmetic_chemist or showcasing her favorite ingredients to small brands and home formulators at simply-ingredients.com. Her email is: askvalerie@icloud.com