If you are confused about the safety of the sodium benzoate preservative when in contact with ascorbic acid (aka vitamin C) or citric acid, you are not alone. There is a tremendous amount of inaccurate information circulating on the Internet and among ingredient-conscious consumers. There is good news! I was able to get to the bottom of this concern and filter out myth from real science.
Hint: Benzene may form only when sodium benzoate and ascorbic acid are present in the same product. It must be ascorbic acid for this to occur, NOT citric acid, and here is why…
Let me start by telling you the reason it is important to look into this. The International Agency for Research on Cancer (IARC) classifies benzene as a Group 1 human carcinogen (source). A lot of cosmetic products contain both sodium benzoate and citric acid. Is this a problem backed by scientific research, or is this simply an internet scare gone viral? This is what I set out to find out.
The backstory of sodium benzoate used as a preservative
Soft drink survey
To begin, the sodium benzoate preservative controversy started in 2005 when some soft drinks tested positive for carcinogenic benzene.
According to the FDA website, the FDA first became aware that benzene could form in some drinks in the early 1990s.
In November 2005, the FDA examined the results of a survey of benzene levels in soft drinks. According to the FDA, the vast majority of the drinks sampled (including those with both benzoate salts and ascorbic acid) contained either no detectable benzene or levels well below 5 ppb. This is the EPA’s level for benzene in drinking water.
To put things in perspective, California’s public health goal for benzene is 0.15 ppb. This number is based on scientific research as to the long-term health effects of benzene exposure. It does not take into consideration what industry lobbyists might want (source).
The result of the soft drink survey
This survey generated a lot of publicity. People started thinking that the same chemical reaction could occur in cosmetic products. Because of the fact that citric acid and ascorbic acid are very similar, people voiced their concerns on the Internet. The cause of the worry was the presence of citric acid in the products that contained sodium benzoate.
By the way, as a result of the publicity, soft drink manufacturers either discontinued the use of sodium benzoate or reformulated those products that had higher benzene levels. The FDA continued testing soft drinks after the initial survey. They found that benzene levels were less than 1.5 ppb (source).
What stimulates the formation of benzene?
Starting in 1993, there have been a lot of studies to determine specific benzene formation mechanisms. Most studies indicate the best candidates for benzene formation. They are conditions with elevated temperature and light where ascorbic acid and benzoic acid or potassium or calcium or sodium benzoate preservative are present. In addition, traces of copper and iron may catalyze reactions between ascorbic and benzoic acid or benzoate salts (source).
Furthermore, it is important to note that while there is a detailed account of the chemical reaction that forms benzene, there is no mention of citric acid. Ascorbic acid is the culprit.
In 2006, the American Beverage Association published guidelines for beverage manufacturers. These guidelines were to help them to reduce or inhibit the formation of benzene in their products. One of the most important guidelines involved replacing ascorbic acid with another antioxidant. Another one was about adding EDTA or sodium polyphosphates to chelate the metallic ions that catalyze hydroxyl radical formation. The third guideline was to review the storage conditions and shelf life to minimize product exposure to high temperatures and ultraviolet (UV) light.
Sodium benzoate preservative in skincare products
Should we be concerned about ascorbic acid and sodium benzoate preservative reaction in skincare products?
I must say that when I determine whether a product is safe enough to recommend for you to use, I look at every ingredient. Although the Skin Deep database is a good starting point, it has certain shortcomings for which we consumers should account. (You can read more about how to use the Skin Deep database to get accurate information here.)
Sometimes the best way to get accurate information is to go directly to the source, namely, scientific studies. The Cosmetic Ingredient Review (CIR) Expert Panel publishes their reviews of scientific studies in CIR reports. You can find them on the CIR website.
The CIR report on sodium benzoate preservative describes a test to examine benzene formation in the beverage samples. The beverages were in the UV stabilized and non-UV stabilized packaging. Some of the samples had 0.04% benzoate and 0.025% ascorbic acid in water. As a result, under intense UV light benzene levels increased by as much as 53%, whereas the use of UV stabilized polyethylene terephthalate bottles reduced benzene formation by approximately 13%.
Since the CIR mentions this in the report, it would be a good idea to avoid skin products with both ascorbic acid and sodium benzoate preservative in them. The CIR report does not mention that a reaction between citric acid and the preservative in question can produce benzene.
Citric acid in personal care products
I must tell you, it is such a relief to know this! In my 7 years of researching personal care and skincare products, I have discovered that most personal care and skincare products contain citric acid. For example, my survey of popular baby wipes brands showed that every baby wipe formulation had citric acid in it. And sodium benzoate preservative is a common choice for baby wipes manufacturers. It protects their products from bacteria contamination. Citric acid is important to regulate the pH of a product, and its quantity is usually very small.
Conclusion about citric acid and sodium benzoate preservative
In conclusion, we do not have to worry about citric acid and sodium benzoate preservative. The concern about carcinogenic benzene development arises only when ascorbic acid and benzoic acid or benzoate salts interact with one another.
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