Postbiotics, including probiotic fractions and effector molecules, are solutions already used in the dermo-cosmetic field; however, the ambition for the cosmetic industry is to add live probiotics to cosmetic formulas with the expectation of potentially higher performance that would probably be driven by a dialogue between added living-microbes and host cells.

However, the use of probiotics as cosmetic ingredients raises many questions. From a formulation standpoint, the first challenge is to maintain these microorganisms alive in a cosmetic formulation. Most cosmetics are water-based and pH neutral or slightly acidic, which can be considered as favorable conditions, but they also contain some ingredients that could affect probiotics ‘survival’: surfactants, chelating agents, glycols, preservatives, fragrance. Moreover, the preservation of cosmetic products from microbial contamination and proliferation is a safety and regulatory requirement. Therefore, the challenge is to maintain probiotics alive in cosmetic products while preventing the growth of microorganisms that could adversely affect the health of the consumers. This can be achieved by different means such as the encapsulation of probiotics, or the use of suitable packaging where the living bacteria are kept separately and mixed with the formulation at the time of use.

From a regulatory standpoint, the ICCR report indicates that “There were no unique regulations governing cosmetic products or ingredients intended to work specifically with the skin’s (or mucosal) commensal microbiome. Rather, such products are subject to the applicable rules and regulations governing cosmetics in each respective jurisdiction, including those covering both safety and product representation (i.e., claims). Several jurisdictions pointed out that while no distinct regulations exist specific to these products there are general quality standard requirements such as microbiological limits which apply to all cosmetic products, including those containing live or viable microorganisms” [204].

The microbiological limits for cosmetic products are given in an International Standardization Organization (ISO) standard [265]. This document states that although cosmetics are not required to be sterile, microorganisms present in a product should not cause an adverse effect on consumer safety or product quality. Therefore, the manufacturer must respect the Good Manufacturing Practices and take the necessary precautions to limit the introduction of microorganisms from raw materials, processing, and packaging.

In this standard, microorganisms are considered as contaminants that are unintentionally introduced in the cosmetic product and microbiological limits are established to ensure product quality and consumer safety. Therefore, those limits should not apply to probiotics which are well-characterized microorganisms intentionally introduced in cosmetic products to achieve a cosmetic benefit. However, discussions are still ongoing, and some clarification is needed to allow the use of living bacteria as cosmetic ingredients.

The use of live probiotics is one of the major future applications in the dermo-cosmetic industry but not the only one. Each human has his or her own ‘microbial fingerprint’ that is specific to his or her skin and this specific microbiome may influence its homeostasis. The microbiome is the path to an individualized skincare routine.

In this perspective, personalized microbiome-derived cosmetic solutions that would intervene specifically are the future paradigm for safe, effective, and successful skin/scalp care products.

Research is at the dawn of a «new generation» cosmetic that will use the skin’s microbiome to provide lasting products with new efficient performance. To bring to light this rising cosmetics category that harnesses the potential of the cutaneous microbiome, it is essential to dissect the dynamic interactions existing between microorganisms and the interplay host/Microbiome. Researchers would also need to understand the regulatory/safety framework to translate these innovations (Figure 2). However, only rigorous and unbiased experimental approaches considering the specificity of the skin-microbiome environment can be applied. This discovery will be made possible by coupling multi-omics technologies, statistical data mining, and representative 3D skin models. These approaches may provide the opportunity to establish microbiome/skin condition causality and, subsequently, cosmetic solutions. The consideration of subtle regulatory environments and country-specificities will also be of high concern.

Figure 2. Resuming the best strategy for a successful translation of Microbiome-based concepts into cosmetic products of the future. Combined approaches of multi-omics technologies, powerful data mining tools, and representative 3D vitro skin models associated with standardized and unbiased experimental approaches dedicated to skin Microbiome analysis are key. Harnessing recent scientific breakthroughs and deciphering the famous causality question allied to better characterization of the interaction between the microbiome, the immune system and skin cells in various skin conditions would accelerate the translation. Finally, consideration of regulatory and safety aspects related to these new/targeted Microbiome-derived technologies (postbiotics, phages, probiotics…) and how to leverage their performance in different formulation types is essential.