Proposed Method to Evaluate the Microbiological Stability of Cosmetics During Use

May 1, 2014 | Contact Author | By: Nadine Bresciani, Valérie Poulet and Nathalie Collard, Anemcoli, Lille, France; Raphaél Dugue, Laboratoire Midac, Loos, France
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Title: Proposed Method to Evaluate the Microbiological Stability of Cosmetics During Use
Use testx microbiological stability assessmentx AETx MUTx protocolx samplingx susceptibilityx contaminationx
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Keywords: Use test | microbiological stability assessment | AET | MUT | protocol | sampling | susceptibility | contamination

Abstract: The authors propose an approach to assess the microbial stability of a product during use, referred to as the Microbiological Use Test (MUT), and apply this analysis in case studies to predict the microbiological risk of commercial products. The described test has been used successfully in the development of cosmetics.

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N Bresciani, V Poulet, N Collard and R Dugue, Proposed Method to Evaluate the Microbiological Stability of Cosmetics During Use, Cosm & Toil 129(4) 56-64 (May 2014)

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The aim of antimicrobial efficacy testing (AET) performed during cosmetic product development is to predict microbial stability and consumer safety during use. The AET design includes referenced microbial strains and acceptance criteria. However, such tests do not include specific situations resulting from consumer use; for example, microbial flora encountered in normal environments; repeated insults; environmental condition variability; the impact of accessories and packaging; and the possibility of localized inoculation, e.g., via caps.

Therefore, it was deemed necessary to develop an additional test to strengthen the investigation. Here, the authors propose an approach to assess the microbial stability of a product during use, referred to as the Microbiological Use Test (MUT), and apply this analysis in a few case studies to predict the microbiological risk of commercial products. The described test has been used successfully in the development process of cosmetic products.

Experimental Design

The MUT test assesses, during the product development phase, the ability of a product to prevent its own microbial contamination during “standard” conditions of use. The aim is to perform a quantitative and qualitative assessment of potential contamination after a specified period of use. To ensure results, some parameters must be fixed; for example, blind testing, to ensure the product is used under conditions close to reality. Panelists should not be informed of the aim of the study—especially that the product will be microbiologically tested upon return. Also, packaging must be as close as possible to the final form, including being comprised of the same materials and utilizing the same closure system. This is a key point, as packaging plays an important role during product use and, therefore, in product contamination.

Timing and conditions also are important. Samples should be returned directly to the microbiological laboratory without extra manipulation prior to testing. The time between the last use and the first test must be fixed, e.g., 72 hr, to limit the recovery of transient microbes but allow for the detection of the more critical persistent contaminants. Further, it is necessary to have at least 20 samples involved to ensure a relevant assessment.

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Table 1. Levels of Contamination

Table 1. Levels of Contamination

Five levels were arbitrarily assigned by the authors based on the % of positive returned samples. For example, Level 1 was assigned to the most robust products.

Table 2. Aqueous Product Assessment

Table 2. Aqueous Product Assessment

First, each product will have a resistance level rating from 1 to 5 based on the first susceptibility testing. Then, based on the second testing, an additional rating will be assigned: A or B for aqueous products; A, B or C for anhydrous products.

Table 3. Anhydrous Product Assessment

Table 3. Anhydrous Product Assessment

First, each product will have a resistance level rating from 1 to 5 based on the first susceptibility testing. Then, based on the second testing, an additional rating will be assigned: A or B for aqueous products; A, B or C for anhydrous products.

Table 4. Selected Products

Table 4. Selected Products

Specific choices were made to improve the feasibility and discriminant power of the MUT model. The chosen products and their basic information are included here.

Table 5. Microbial Stability During Use

Table 5. Microbial Stability During Use

Results of the MUT assessment are summarized here. No contamination was found after the use of a face and body cream or a foundation (5). The two most contaminated products were the foaming gel (2) and shower cream (3).

Table 6. Identification of Contaminants

Table 6. Identification of Contaminants

Contaminants were isolated and identified, and results are summarized here. The authors noted a large proportion of cocci coming from the cutaneous flora, which are directly linked to use. Also observed was the fact that, among the recovered microorganisms, only one was specified: Staphylococcus aureus (1/22 Staphylococci recovered).

Table 7. Final Product Assessments

Table 7. Final Product Assessments

Shown here are the final product assessments. Interestingly, none of the tested products were rated as Suitable (S). The face and body cream, foundation and lip gloss were classified as RU, whereas the face cream, foaming gel, shower cream and refreshing lotion were classified as IC.

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