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Sodium Benzoate and Ascorbic Acid and How They Mix

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The combination of sodium benzoate and ascorbic acid has been an ongoing topic in the food, personal care, and pharmaceutical industry for years. While both of them alone are determined as safe ingredients by the FDA, the interaction between them can produce the devil – benzene. In order to prevent the formation of this toxic compound, here are a few things that we need to know.

So, what is sodium benzoate?

Sodium benzoate is a preservative with a long history. On its own, it’s not to be feared. It is the first preservative that the FDA determined was safe to use in food and personal care. One advantage of sodium benzoate is that it can be easily derived from nature, which makes it compatible with a natural certificate (No wonder it became so popular with the all-natural/organic ingredients skin care trend!). Sodium benzoate can be commonly found in food, beverages, medicines, and plenty of personal care products.

Sodium benzoate effectively inhibits the growth of bacteria, mold, and microbes. Among all the categories, sodium benzoate is proven to work remarkably well with acidic goods. In skincare, it helps prevent corrosion and sometimes even save the metallic-material packages from rusting.

Ascorbic Acid

Ascorbic acid is a type of vitamin C. Among all types of vitamin C, ascorbic acid is scientifically proven to have the most outstanding skincare benefit in peer-reviewed studies. It is the most biologically active form of vitamin C and has a remarkable performance on topical use. Its benefits include fighting free radicals, reducing signs of aging, and brightening the skin.

The flaw of ascorbic acid is its instability, particularly under exposure to air and light. Continuous exposure under light and air can wear off all of its potency. As a result, all skincare products that contain ascorbic acid are supposed to be packaged in opaque and airless containers such as a needlehead tube.

How Does Vitamin C React with Sodium Benzoate?

When ascorbic acid mixes with sodium benzoate, a reaction called decarboxylation takes place. This reduces the amount of benzoic acid and forms benzene. Benzene is a frightening compound since it’s medically proven to be a carcinogen. Although the amounts of benzene likely to form from a 15% vitamin C product and a 0.25% sodium benzoate product are likely to be very small, and likely not to be harmful in such small doses, it’s something I know readers are concerned about, so we’re addressing it here.

Can the Reaction Between Sodium Benzoate and Ascorbic Acid Be Prevented?

Yes, theoretically. But no, in practice.

Let me explain.

In theory, during the chemical reaction between sodium benzoate and ascorbic acid, certain procedures and formulation adjustments can be made to prevent these two compounds from reacting. For example, in beauty products, if we pair a very high concentration level of ascorbic acid (above 25%) with a very low concentration level of sodium benzoate, we can prevent the two from reacting at all. Under this condition, vitamin C serves as a powerful free radical scavenger instead of contributing to the chemical reactions with sodium benzoate.

However, in terms of skincare, according to the research done by dermatologists at Duke University Medical Center, ascorbic acid’s “maximal concentration for optimal percutaneous absorption was 20%.” In other words, as long as we want ascorbic acid to work in our skin care products, it can’t exceed the level of 20%.

So, in theory, you can prevent sodium benzoate and ascorbic acid from reacting by using really high concentrations of ascorbic acid. But ascorbic acid only is absorbed up to 20% in the skin. So you’re not really likely to ever see a preventable reaction on the basis of vitamin C concentration.

pH and Benzene Formation

Another important factor is the pH value. Skincare products with a pH of 3 or above are less likely to form benzene than products with a pH of 2 or less. At a pH level above 7, it can prevent any benzene from forming at all. However, this means nothing to ascorbic acid users, because ascorbic acid must be formulated at pH levels less than 4.5 to enter the skin. In fact, most ascorbic acid skin care products on the market today only have a pH range of 2.6 to 3.2 — far below the pH value of 7 that we expect to stop the formation of benzene.

Why I Prefer Acidic Forms of Vitamin C

It’s the same reason why I never recommend using vitamin C in non-acidic form, because once the Vitamin C gets a pH of 3.5 and above, it can’t be absorbed but only sits on the surface on our skin. This also applies to the DIY mask with acidic fruits such as oranges. For example, oranges are rich in vitamin C, but in general they have a pH value between 3 and just above 4 (to 4.5 or so).

If you apply an orange to your face that has a pH value above 3.5, it pretty much will not give you any significant vitamin C benefits like skincare products do. Therefore, sometimes it’s a good idea to stick with the chemically formulated skin care products rather than DIY with natural ingredients.

I Also Avoid Benzoic Acid, Benzene, and Benzoate with Ascorbic Acid

In addition to the important factors like pH value and concentrations, we can simply avoid the benzene by paying attention to the ingredients of our skincare products. For me, I will not give up ascorbic acid because of its extraordinary benefits on skin. Instead, I just avoid any form of sodium benzoate in other products, so they don’t mix together while I’m using my skincare routine. But you need to be careful: If you want to avoid sodium benzoate, look for the words ‘benzoic acid,’ ‘benzene,’ ‘sodium benzoate,’ or ‘benzoate.’

Watch Out for Heat and Light

Last but not least, the FDA states that exposure to heat and light can stimulate the formation of benzene. So just like any beauty product, skincare that contains ascorbic acid should be stored in a cool, dark place in order to prevent the benzene from forming.

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