Is Potassium Benzoate Dangerous?

Is Potassium Benzoate Dangerous?

What is Potassium Benzoate?

Potassium Benzoate, is a preservative that is used to keep beverages fresh and safe. It protects against yeasts, moulds, and certain types of bacteria. It is commonly found in soft drinks, salted margarine, olives, sauces and relishes, jams and jellies, pastry and pie fillings, and low fat salad dressings.

What are the Possible Health Issues?

When exposed to heat and light, some products that contain both potassium benzoate and ascorbic acid (vitamin C) may produce benzene. This is a concern because benzene is a known carcinogen. It causes cancer in humans.

Do the Claims Against Potassium Benzoate Make Sense?

To answer this question, we need to look at the chemical compositions of potassium benzoate, ascorbic acid, and benzene:

  • Potassium Benzoate = C7H5KO2
  • Ascorbic Acid = C6H8O6
  • Benzene = C6H6

Now, if you’re like me and your chemistry knowledge is fuzzy at best, what this means is that potassium benzoate is composed of 7 carbon atoms (C), 5 hydrogen atoms (H), 1 potassium atom (K), and 2 oxygen atoms (O).
So, if the claims are accurate, we would expect that:
C7H5KO2 + C6H8O6 + (heat and light) -> C6H6 + some other stuff
In other words, do the potassium benzoate and ascorbic acid contain the right kinds of atoms to produce benzene? Obviously, the answer is yes, but there is a bit more to it than that.

Most of the time, chemicals are happy being just what they are. The bonds between the atoms are strong, and something needs to happen to break these bonds and force the atoms to recombine in new structures.

In this case, we have the possibility of heat and/or light affecting the molecules. And, as it turns out, we can also add trace amounts copper or iron found in the water (or from cans) to our equations.

What we find is that:

  1. The ascorbic acid reacts with the copper in the water to produce copper ions.
  2. A copper ion + benzoate ion, react to give a new copper ion + CO2 + benzene. (This reaction is heat sensitive, and so proceeds more rapidly at higher temperatures.)
  3. The process continues until either the ascorbic acid, copper, or benzoate has been used up.

Since there are usually only trace ammounts of free copper ions in solution, it’s going to take a long time to make even ppm amounts of Benzene.

Also note that strongly acidic conditions promote the formation of benzoic acid, in solution, instead of benzoate ions. Therefore, this reaction will probably not occur because the benzoic acid is not susceptible to being reduced by this method.


My chemistry knowledge is definitely rusty, and a lot of this almost seems like magic to me. However, in my opinion, the formation of benzene is definitely possible. It may be produced is very tiny amounts, but any amount is probably too much. Who knows what the cumulative effect might be?

Limiting the amount of canned soft drinks containing potassium benzoate (or sodium benzoate since the reactions are the same) would probably be a really wise decision.

What’s your opinion? Does anyone have a better understanding of the chemistry involved>


  1. FDA Questions and Answers Regarding Benzene in Soft Drinks
  2. US National Library of Medicine
  3. UK Food Guide


If you want to read more, try the following links…

  1. Fireworks ingredients
  2. Potassium Benzoate Supplier – FBC Industries Inc.

Canadian Food Additive Dictionary
FDA Food Additive Status List
UK Foods Standards Agency, Approved Food Additives
Food Standards – Australia and New Zealand

Posted in Food Additives, Ingredients, Preservative
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  1. […] Potassium Benzoate.When you combine heat and light to potassium benzoate and vitamin C it could produce benzene. Benzne is known to cause cancer. […]

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