Sodium benzoate is a preservative used in cosmetic and skin care products that also functions as a corrosion inhibitor.
Sodium benzoate is the sodium salt of benzoic acid. Benzoic acid was discovered in the sixteenth century. Both benzoic acid and sodium benzoate occur naturally in many foods. For example, fruits and vegetables can be rich sources, particularly cranberries, prunes, plums, cinnamon, ripe cloves, and apples. Other sources include seafood and dairy products like milk, cheese and yogurt.
Sodium benzoate is a white, crystalline solid and is a hygroscopic material. It will easily dissolve in water, forming a transparent, colorless solution. This ingredient is primarily used as a preservative in food and cosmetic products. In fact, sodium benzoate was the first preservative allowed by the FDA for use in food products.
Sodium benzoate functions as a preservative and a corrosion inhibitor in numerous types of cosmetics and personal care products.
As a preservative, sodium benzoate prevents bacteria and fungi from developing in products. The mechanism starts with the absorption of benzoic acid into the cell of a microorganism. If the pH inside the cell falls to 5 or lower, the anaerobic fermentation of glucose through an enzyme called phosphofructokinase decreases sharply. This inhibits the growth and survival of microorganisms that can cause products to spoil.
Sodium benzoate also functions as a corrosion inhibitor, which means it helps to prevent the corrosion (rust) of metallic materials used in cosmetic packaging.
The Food and Drug Administration (FDA) includes sodium benzoate on its list of direct food substances affirmed as Generally Recognized As Safe (GRAS).
The safety of sodium benzoate has been assessed by the Cosmetic Ingredient Review (CIR) Expert Panel. The CIR Expert Panel concluded that this ingredient is safe for use in cosmetic products.
One potential problem with sodium benzoate is if this ingredient is formulated with vitamin C. When sodium benzoate is combined with vitamin C, a chemical reaction occurs that forms benzene. Benzene has been identified as a carcinogen. According to a publication in the International Journal of Occupational and Environmental Health, benzene-induced cancer in humans was first reported in the late 1920s.
The reaction between sodium benzoate and vitamin C was first discovered in the early 1990s. The major concern about this reaction was mostly focused on the presence of these two ingredients in soft drinks. In fact, 2.5% of 200 soft drinks with vitamin C and sodium benzoate were found to have levels of benzene above allowable levels, according to the FDA.
So is the presence of sodium benzoate and vitamin C in a skin care product a major concern? The answer is unclear. This is because there are ways of formulating products that can prevent this reaction from occuring. For instance, according to FutureDerm, benzene does not form at all if you use beauty products with a very high concentration of vitamin C and a low concentration of sodium benzoate. This is because higher amounts of vitamin C cause it to act as a free radical scavenger instead of reacting with sodium benzoate. In addition, products formulated with a pH of 3 or above are safer than those with a pH of 2 or less. And above a pH of 7, no benzene forms at all. Lastly, protecting products from light or heat exposure can limit the chances of benzene formation. Manufacturers that follow safe practices can effectively prevent benzene in their products.
Aside from the problem with vitamin C, there is also some evidence that suggests sodium benzoate may damage cells on its own. A study conducted by Peter Piper, a professor at Sheffield University in the UK and an expert in molecular biology and biotechnology, found that sodium benzoate increases production of free radicals. Free radicals are highly unstable, reactive species that can damage important cellular components, such as DNA, cell membranes, proteins, etc. In this study, Piper discovered that sodium benzoate appeared to attack the mitochondria of cells, damaging their ability to prevent oxygen leaks that create free radicals. Yeast cells were used because of their similarity to human ones, but no research on humans has been done. Further studies will need to be completed in order to determine if sodium benzoate is a health hazard.
References: Wikipedia, “Benzoic Acid”, Biotechnology and Health Sciences, “An Overview on the Effects of Sodium Benzoate as a Preservative in Food Products”, Biochem J. 1983 Sep 15; 214(3): 657–663., Cosmetics Info, “Corrosion Inhibitor”, Livestrong, “The Truth About Sodium Benzoate & Benzene”, 2017, FutureDerm, “Do Vitamin C and Sodium Benzoate Together Form a Carcinogen?”, 2012, Truth In Aging, “Sodium Benzoate”.