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An introduction to Preservatives and Product preservation
An introduction to Preservatives and Product preservation by Scott Grainger of Cosmetic Safety Consultants Ltd
Why preserve cosmetics?
Many cosmetic formulations can support microbiological growth by providing the two main conditions required – a source of food (fats, carbohydrates, proteins etc.) and a source of water. ‘Microbe’ is the general name given to microscopic organisms such as viruses, bacteria and moulds (which include fungi and yeasts). The presence of microbes in cosmetic products should be avoided for two important reasons
• Spoilage – the physical and chemical integrity of the product can be compromised. This can mean changes in viscosity, colour, odour, pH changes etc. resulting in a final product that is no longer suitable for the purpose it was created.
• Safety – in some cases, the microbes that contaminate cosmetics are pathogenic – in other words they are potentially harmful to human health. If used by vulnerable users, applied to broken or damaged skin or mucous membranes, there is a real risk of infection to the end user – in some cases very serious infection can result.
What sort of products need preservation?
Any cosmetic product that provides an environment which is capable of supporting microbial growth should be preserved. Specifically, all products that contain water (and do not possess other chemical or physical properties that prevent microbial growth) should be preserved appropriately.
Self-preserving formulations
These are products that by the nature of their ingredients / compositions do not support microbial growth. The simplest example of a formulation for which preservation is not required is one in which there is no water – zero water content (anhydrous) simply means no microbial growth – all microbes need water to survive, and without it, there can be no proliferation. One disadvantage of this method of formulation is if a product is to be used in an environment where there is the potential for water to enter the product – for example, an anhydrous, oil or butter based scrub used in the shower – if water does enter the product during use, then, depending on the formulation, there is subsequent potential for microbial growth.
Water activity
Some products that contain water can be self-preserving because they contain substances that reduce the ability of microbes to access / use the water that is present to proliferate. These substances include humectants such as glycerin, salts and sugars, some gums and alcohols.
pH
This is a measure of how acidic or alkaline a product is – Below pH 7 is acidic, above pH 7 is alkaline and pH 7 is described as being pH neutral. Most microbes prefer around neutral pH to grow, so it follows that it is possible to limit or eliminate growth potential by controlling the pH of a product. pH below 4 and pH above 9, generally produces an environment that limits microbial growth – there may still be requirement for additional preservation when using this method, depending on the product type / formulation.
Detergents (and soaps)
The presence of detergents can help to preserve a cosmetic formulation by reducing surface tension at and damaging the outer surface of the microbes – the outer surface protects and keeps the microbes intact and able to survive.
Alcohol (fragrances) and solvents (nail polishes)?
It should be noted, that the properties described above to create self-preserving products are generally used in combination for best results. For example, a liquid soap with pH above 9 and a high concentration of soap salts is effectively self-preserving – providing it isn’t neutralised or over-diluted.
Types of preservatives
Very generally, most preservatives work by affecting the outer surface of microbes – they may compromise the structure or inhibit reactions that are vital to cell metabolism. Preservative choice is limited to those detailed in Annex V of REGULATION (EC) No 1223/2009 OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 30 November 2009 on cosmetic products. The Annex lists the preservatives that are approved for use in product manufactured in the EU, and provides details of concentration limits and product categories, where appropriate. The preservative systems that are used most regularly in products produced on an artisanal scale are the following - Phenoxyethanol, Sorbates, Benzoates, Salicylates, Benzyl Alcohol and Dehydroacetic acid. These preservatives are universally approved and have a long established safety profile. When choosing a preservative system it is important to check the supplier information and make sure that it is suitable for your product. For example – does the preservative function properly at your product pH? Is the preservative water or oil soluble? Is the preservative affected by the presence of surfactants? Is it broad spectrum - i.e. does it control all categories of microbes or is it specific to bacteria? In this case you would need to include a second preservative that is effective against moulds, for example. All of this information is readily available from the preservative manufacturers, and suppliers generally take these factors into account when selling preservative mixtures to their customers.
Natural and alternative preservatives
There are many naturally occurring substances that have anti-microbial properties - Essential oils, fragrance compounds (synthetic and naturally derived), fatty acids and more recently, by-products of fermentation of natural plant and vegetable matter are a few examples. Most of these substances are not actually included in the Regulation Annex, so there can be some discussion about whether or not they are present in a formulation specifically as a preservative, or if they are present in the formulation as an anti-microbial agent and hence producing a product that is effectively “self-preserving”. As the only preservatives legally permitted are those detailed in Annex V of the regulation, the latter must be assumed in order for these products to be used legally. From a marketing point of view, term such as “naturally-preserved” or “free from x, y, z” can be useful – The labelling name of many fragrance derived “preservatives” is simply “Parfum” – this does have appeal of course but care should be taken not to mislead the consumer by using claims such as “chemical free” or “preservative free” as these are quite specific claims and could lead to further investigation by a competent authority.
Challenge Testing (CT) or Preservative Efficacy Testing (PET).
If a product is preserved, usually there is a requirement for this test. Contrary to popular belief, CT/PET is not primarily a test of the microbiological purity of your finished product – this can be done cheaply and quickly with basic microbiological testing such as TVC (Total Viable Counts) and SPT (Specific Pathogen Test). Instead, CT/PET is a measure of how well your chosen preservative can deal with the introduction of microbial contamination during use. When you place even the cleanest of fingers into a jar of face cream, for example, you transfer micro-organisms that occur naturally on the skin and in the environment to the product. The preservative system needs to be adequate to prevent any of these incidental microbes from growing and contaminating the product. This is why CT/PET is such an important test – it verifies that your product is microbiologically safe during continued use and the end user is protected. In some special cases, CT/PET might not need to be performed – if the product is packaged into sterile, single-use containers, then CT/PET is not required – the product is used entirely in one application and hence there is no need to study how the preservative system copes over time and subsequent use. The second feasible way in which CT/PET can be avoided is by the use of sterile, airless pump style containers – the design and use of these containers means that there is negligible potential for the introduction of microbial contamination during continued use.
Vitamin E
A final word on Vitamin E. As safety assessors, we see numerous formulations submitted that include Vitamin E as the sole “preservative”. Whilst it is true that tocopherols do show some anti-microbial activity, their primary function in cosmetic formulations is antioxidant. They are useful in preventing oils and fats becoming rancid due to oxidation from contact with air (oxygen) but they are not reliable preservatives with regard to controlling microbial growth.
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