This is often the first and most important analysis performed for cosmetic products. The requirement to test the microbiological purity of cosmetic products and raw materials intended for their production results from Regulation (EC) No. 1223/2009 of the European Parliament and of the Council and is valid throughout the European Union. The results of this analysis determine whether a given product will be allowed on the market.
The testing methodology is defined in the standard PN-EN ISO 17516:2014-11 Cosmetics – Microbiology – Microbiological limits (this standard applies to all cosmetics, excluding low microbiological risk products referred to in PN-EN ISO 29621:2017-04 Cosmetics – Microbiology – Guidelines for risk assessment and identification of low microbiological risk products – in the case of these products, microbiological tests do not have to be performed).
General testing guidelines are also included in the PN-EN ISO 21148:2017-07 standard.

When testing microbiological purity, standardized strains and research methods should be used:

• • PN-EN ISO 16212:2017-08 Cosmetics – Microbiology – Enumeration of yeasts and moulds,
  • PN-EN ISO 21149:2017-07 Cosmetics – Microbiology – Enumeration and detection of mesophilic aerobic bacteria,
  • PN-EN ISO 18416:2016-01 Cosmetics – Microbiology – Detection of Candida albicans,
  • PN-EN ISO 18416:2016-01 Cosmetics – Microbiology – Detection of Candida albicans,
  • PN-EN ISO 18416:2016-01 Cosmetics – Microbiology – Detection of Candida albicans,
  • PN-EN ISO 18416:2016-01 Cosmetics – Microbiology – Detection of Candida albicans,
  • PN-EN ISO 18415:2017-07 Cosmetics – Microbiology – Detection of specific and non-specific microorganisms.
  • Total microbial count (mesophilic bacteria and yeasts and molds)
  • EN ISO 22717 - presence of Pseudomonas aeruginosa
  • Presence of Staphylococcus aureus
  • Presence of Candida albicans
  • Presence of Escherichia coli

In the European Union, including Poland, the law on cosmetic products is regulated by Regulation (EC) No 1223/2009 of the European Parliament and of the Council of 30 November 2009. According to this regulation, the manufacturer is obliged to have the results of product challenge tests, i.e. to carry out the so-called Maintenance Test. This analysis is performed to check the effectiveness of the preservative or preservative system used to preserve the product. The challenge test was designed primarily for products posing a high microbiological risk, including cosmetics based on water. The study involves the use of five pathogenic microorganisms (three bacteria, a yeast-like fungus and a mold fungus) in an appropriate concentration and volume, applied to a cosmetic product placed in a substitute package for the duration of the study and measuring changes in the number of microorganisms obtained at set time intervals.
The most well-known and most commonly used method in the cosmetics industry is the Challenge Test (PN EN ISO 11930:2012). This method reproduces on a laboratory scale the microbiological aggression that a product may be subject to during production, storage and use, which allows for the assessment of the antimicrobial protection of the cosmetic.

Cosmetic products are not designed and created to protect the user from microbiological threats by definition. However, cosmetics sometimes have additional properties that positively affect the reduction, increase safety or support and care in the treatment process of selected diseases, mainly skin diseases. In such a situation, it is necessary to prove the effectiveness of the cosmetic product against the strains responsible for the reduction or protection of the manufacturer's declared effect. The most recognizable and popular cosmetics from this group are products dedicated to acne skin. 
Acne is a chronic and multifactorial inflammatory disease of the skin and the pilosebaceous unit. Studies have shown that in the age group between 11 and 30 years, this disease may affect 80% of people. The pathogenesis of acne is extremely complex. The causes of acne vulgaris include: seborrhea, hyperkeratinization of the pilosebaceous glands, hormonal factors, increased inflammation and colonization of the sebaceous units by the bacteria Cutibacterium acnes. Dysbiosis in patients with acne is associated with a reduced number of S. epidermidis cells and excessive colonization of the sebaceous unit by C. acnes cells. 
The latest studies seem to confirm the beneficial role of S. epidermidis in the pathogenesis of acne by limiting skin colonization and inflammation caused by C. acnes. Acne skin requires proper, comprehensive and systematic care. Innovative anti-acne cosmetics are expected to be able to improve the skin microbiome – restore the balance between S. epidermidis and C. acnes. This will reduce inflammation and improve the skin's condition. Examples of products for which it is recommended to perform additional analyses confirming the effectiveness of the preparation are cosmetics dedicated to use during the treatment of seborrheic dermatitis or e.g. mycosis.

A healthy, healthy skin microbiome is characterized by high species diversity and a balance in the quantitative ratios between individual microorganisms. Dysbiosis refers to an imbalance in the skin microbiome, which can lead to the onset or development of diseases such as acne vulgaris, rosacea, psoriasis, seborrheic and atopic dermatitis, or even alopecia areata.
The skin microbiome is influenced by many factors. Microbiota colonization begins at birth and its composition is influenced by the mode of delivery. This composition is then determined by several internal (ethnicity, gender and age) and external factors (lifestyle, hygiene habits, cosmetics used, antibiotics taken, geographical location, climate and season). Differences in the skin microbiome of people living in different environments (rural or urban) are observed: the skin microbiota of people living in industrialized countries is much less diverse.
Important factors negatively affecting the diversity of microorganisms on the skin surface are also antibiotics, which can change the composition of bacteria inhabiting the skin, including the commensal bacteria Staphylococcus spp., which are known to compete for colonization with the pathogenic Staphylococcus aureus.
The condition of the skin microbiota is also influenced by hygiene and cosmetic treatments performed using chemical substances that remove skin microflora, and the resulting changes in physicochemical conditions on the skin surface hinder the recolonization of commensal microflora, while creating favorable conditions for the colonization of the skin by pathogens.
The skin microbiome is a very diverse environment, influenced by many factors. The right products should be selected based on an individual assessment of the condition of our skin. However, there are some universal features that we can follow. We should mainly focus on gentle products that do not disturb the skin's natural pH and those that take care of its hydration.
There is an increasingly clear tendency among cosmetics manufacturers to provide information on the product's impact on the skin microbiome.

At MPR Labs, we offer a service that can confirm such a declaration. This is possible thanks to the performance of appropriate microbiological analyses, during which participants use a given cosmetic for four weeks without changing their diet, lifestyle or habits. Comparing the skin microflora before applying the product and after its monthly use allows us to determine how the product has affected the microbiome of our skin. Products recommended as having a positive effect on the skin microbiome can provide real support for its reconstruction and protection.