p>Preservatives are a necessary ingredient in cosmetics and personal care products to maintain a products integrity and stability. They work by inhibiting or reducing the growth of microorganisms such as bacteria and fungus. The reality is that most products sold sit for extended periods of time prior to them being sold. A cosmetic manufacturer needs to give adequate preservation to account for this so that the consumer uses it prior to it becoming unfit for use. This is particularly true for products that contain water, such as many conditioners and moisturizers, and other active ingredients (antioxidants and emulsifiers) that would otherwise lose their effectiveness and stability over time.
Potassium sorbate has been used for a long time in the industry but has recently gained more attention in green beauty products. Often these products have some kind of natural story or toxin free philosophy to them and so they look for what they perceive to be “natural” for their preservation of choice.
How natural is the potassium sorbate used in cosmetics?
Potassium sorbate is the potassium salt of sorbic acid. Sorbic acid was originally found in the Rowan berries from the Rowan Tree. The name for Sorbic acid comes from the latin name for the rowan tree. Sorbic acid is an unsaturated fatty acid and as such is subject to oxidation , therefore the use of an antioxidant like Vitamin E is recommended when you are using it in formulas. It is also sensitive to UV light and may turn yellow in solution.
The potassium sorbate in your cosmetic products however is synthetic and is a “nature identical” synthetic molecule. The potassium sorbate used in cosmetics is synthetically produced and any company selling your Potassium Sorbate who declares it is natural I would be asking for “proof”. I have yet to find a natural potassium sorbate supplier. Whether a chemical is synthetic or natural in origin makes no difference to the way it functions or performs. There are many who would like to believe that the natural source is better metabolized and recognized by the skin. This is not true by any means. Many mistake that the fact that organic cosmetics contain potassium sorbate, therefore it is a natural source. This is incorrect. Organic cosmetics are allowed synthetic preservatives in them. The synthetic preservatives are approved by the organic certification body, so you can’t just put any preservative in and get it approved. It needs to be from their list of approved synthetic preservatives.
Potassium sorbate is predominantly used for killing fungi and mould. It is created by using potassium hydroxide (KOH) to neutralize sorbic acid (C6H8O2). It readily dissolves in water where it converts to sorbic acid, its active form, at a low pH. Sorbic acid is very pH dependent. While it shows some activity up to pH 6 (about 6%), it is most active at pH 4.4 (70%). At pH 5.0 it is 37% active.
Potassium sorbate is not a broad spectrum preservative for cosmetic use and needs to be combined with other preservatives. If potassium sorbate is used as a preservative, the pH of the finished product may need to be reduced for potassium sorbate to be effective. This is because potassium sorbate is the inactive salt form of sorbic acid. To be useful, the pH of the formulation must be low enough to release the free acid for useful activity.
The cart below shows the relative activity of Sorbic Acid at various pH’s.
pH Percentage of Activity
As you can see the activity decreases as the pH increases which means it generally needs to be combined with other preservatives to enhance its efficacy. Potassium Sorbate is used in some of our products combined with other preservatives. It is just one of many preservatives that we use for safe preservation.