Preservative Efficacy Testing
Recent EU legislation, the Cosmetics Directive, has driven the requirement for formulation of cosmetic products to protect them from microbiological contamination that can affect both the quality of the product and its potential to do harm to users of the product.
What are Preservatives?
Preservatives are antimicrobial agents used to prevent or decrease the ability of micro-organisms to grow in your product. There are many different types of preservatives commonly used to preserve food, household products and toiletries and cosmetics. There are synthetic and natural preservatives such as parabens, urea derivatives and vitamins and essential oils. Selection of an appropriate preservative is essential for the quality of the product.
Synthetic preservatives have been around for decades and have successfully preserved thousands of cosmetics. However, products now also include natural preservatives as a result of published toxicity results of some synthetic preservatives. The available selection of natural preservatives is limited, and their properties can vary in terms of effectiveness from manufacturer to manufacturer and batch to batch, and sometimes affect other aspects of the formulation in an undesirable way.
Why do you need preservatives in your product?
Microbes can cause your product to spoil, thus reducing its shelf-life, but more importantly the potential for contamination with potentially pathogenic strains, i.e. those that cause disease and are dangerous to end users, can greatly increase in the absence of preservatives. Cosmetics are well known for their ability to support microbial growth. Water based products with a neutral pH have shown to be the most susceptible. To ensure that this doesnâ€™t happen, cosmetics and personal care manufacturers conduct â€œPreservative Efficacy Testsâ€ also known as PET, Challenge Test or Antimicrobial Efficacy Test.
What is a PET?
A preservative efficacy test or PET (otherwise known as a challenge test) in summary simulates contamination through a serious of inoculations containing â€œchallenge" micro-organisms over a period of time and assesses the ability of the preservative to reduce or eradicate these organisms. There are several different recognised methods as well as numerous known and unknown in-house methods for assessing the efficacy of preservatives.
Preservative challenge tests run for long periods of time and require a great deal of expertise and labour.
Efficacy testing is especially an area that highlights our expertise. We have many packages to suit all product types and budgets.
Here at BluTest we model our standard PET on the ISO 11930 method (Evaluation of the antimicrobial protection of a cosmetic product) and also use this method as a basis for our bespoke PETs. There are other methods available are mentioned in the journal article below â€“ if you would prefer your product to be analysed using a different method we can arrange this for you.
ISO 11930 â€“ A Comparison to other Methods to Evaluate the Efficacy of Antimicrobial Preservation
How is a PET conducted?
Firstly the product is screened for contamination (also known as a bio-burden test, Total Viable Count (TVC), Total Yeast and Mould Count (TYAMC), Test for Specific Micro-organisms (TSM)). At this point we would advise the client if any contaminants were found in the product. We offer an optional from here to identify the particular strain that has caused the contamination and a culturing service to grow the organism of interest so that it can be used as an additional â€œchallengeâ€ organism in the PET Test. Alternatively, if it is known that the manufacturing facility or water supply has known problem organism these can also be added and challenged with the preservative. By customising the method in this way provides you confidence that your products wonâ€™t support microbial growth with the end product user or sitting on the shop shelf.
Another additional step at this point is environmental monitoring and risk analysis of the manufacturing facility. Our dedicated scientists can provide you with their expertise to source the root cause of your contamination problem in order to monitor, reduce or eliminate this risk for you. We can also perform training sessions to allow you to monitor and carry our sampling yourself. If you would like more information on this service and feel that this is applicable to you, enjoy the peace of mind that we can provide by eliminating the stress involved in tackling this on your own.
Once the initial parameters have been confirmed we would carry out a neutralisation and validation step. This is to ensure that the inoculated â€œchallengeâ€ organisms can be recovered from the product. For this method the product is challenged using 3 bacteria (Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa) and 2 fungi (Candida albicans (a yeast) and Aspergillus brasiliensis (a mould)). The validated product is challenged separately with the 5 microbial strains (plus additional strains for the bespoke PET) and the initial concentration of each is determined. The product is then incubated for 7 days. On day 7 the level of the challenge organisms are assessed. This first step can act as a PET screen, to provide you with an indication that you product will pass. To carry out the full PET the product is re-incubated and further assessed on day 14 and day 28 or for bespoke PETs products can be re-challenged at additional time points and incubated for longer periods e.g. up to a year.
All results are collated and statistically reviewed. The desired result is that all of the organisms are killed. In the event that some bugs survive we can provide you with advice on how to proceed.
Why does a PET add value to your product?
A PET report will provide you with valuable information with regards to the performance of your product and can be used as part of your safety assessment to comply with the EU Cosmetics regulation (effective from July 2013).
Links and Useful Resources if you would like to read more on this topic: