Infections of cosmetics during use
The presence of microorganisms in a cosmetic may cause it to separate, change its smell and lose its properties. Moreover, a contaminated cosmetic product poses a health risk to the consumer. Therefore, the quality of cosmetics available on the European Union market is regulated by regulations. In accordance with Regulation (EC) No. 1223/2009 of the European Parliament and of the Council of November 30, 2009, each cosmetic should successfully pass microbiological tests, preservation and stability tests. These analyzes are performed at the Ekolabos Laboratory.
The impact of formulation on the risk of cosmetic contamination
The microbiological resistance of cosmetics to secondary infections depends on many factors. Appropriate product composition, maintenance and packaging can minimize the risk of product contamination during use. The PN-EN ISO 29621:2017-04 standard presents guidelines for risk assessment and identification of products with low microbiological risk. For cosmetics with a low risk of contamination, a stress test does not need to be performed.
Water
According to the mentioned standard, cosmetics with low microbiological risk are characterized by low water activity. For pure water, the value of aw is 1. An increase in the concentration of soluble compounds reduces the amount of water available. As the concentration of dissolved substances increases, aw decreases. This results in an increase in the osmotic pressure of the solution and destabilization of the cell covers of microorganisms. Microorganisms present in an environment with lower water activity than preferred use energy to maintain cellular tension. This involves limiting the number of divisions and thus limiting the development of microorganisms in the product. Most bacteria grow best in an environment with a water activity above 0.95. Yeast prefer environments where aw is in the range of 0.66-0.88. The values of the minimum water activity necessary for the development of individual microorganisms are summarized in Table 1. A drop in aw in the environment below the minimum value for a given microorganism causes cracking of their cell covers, which leads to their death.
| Microorganisms | Minimal water activity |
| Most bacteria | 0,90 |
| Pseudomonas aeruginosa | 0,97 |
| Escherichia coli | 0,95 |
| Staphylococcus aureus | 0,86 |
| Most yeasts and molds | 0,60 |
Table 1. Minimum water activity necessary for the development of individual microorganisms based on PN-EN ISO 29621
Alcohol
The high alcohol content in the formulation causes denaturation of microbial proteins. At concentrations between 10% and 20%, alcohol has a bacteriostatic effect. However, in products with alcohol content ≥ 20%, the growth of microorganisms is inhibited. A preservation test does not need to be performed for cosmetics with a high alcohol content.
pH
Most microorganisms tolerate a wide range of pH in the environment. Maintaining a neutral reaction inside microbial cells is possible by regulating the concentration of hydrogen ions. In the case of extreme pH values in the product, microorganisms use energy to maintain the appropriate concentration of H+ ions. This results in a slower growth of microorganisms. Therefore, products with a pH ≤3 or ≥10 are considered cosmetics with a low microbiological risk and do not need to be subjected to stress tests.
Production and packaging
Factors other than the composition of the cosmetic also influence the risk of product contamination. One of them is the packaging temperature used during production. Cosmetics packaged at temperatures above 60°C have a low microbiological risk. The type of packaging is a very important factor influencing the risk of consumer contamination of a product. Cosmetics in packaging with a dispenser or atomizer pose a lower microbiological risk. They significantly reduce the chances of microorganisms belonging to the skin microflora getting into the product.
Cosmetics preservation test
Load testing of cosmetic products is performed in accordance with the recommendations of PN-EN ISO 11930:2019-03. The purpose of the test is to check the effectiveness of preserving the finished product. The test involves contamination with microorganisms that most often infect cosmetics. The analyzed product is divided into 5 samples weighing 20 g or volume 20 ml. Each of them is contaminated with a suspension of the appropriate microorganism. They are: Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Candida albicans and Aspergillus brasiliensis. This suspension should contain 1×107-1×108 cfu/ml for bacteria and 1×106-1×107 cfu/ml for fungi. Then, after 7, 14 and 28 days, detailed tests are carried out to determine the number of microorganisms present in the sample. It is compared to the number of microorganisms at time T0, i.e. immediately after contamination. This data is necessary to calculate the reduction value presented in logarithm form. For a product to pass the stress test, the number of microorganisms present in contaminated samples should decrease or not increase.
