The skin is our largest organ and the instrument through which we communicate with the external world, the environment that surrounds us. The skin is also a habitat for numerous species of microorganisms, bacteria, and fungi that make up the skin microbiome. It is estimated that the human body contains about ten trillion human cells and one hundred trillion bacterial cells, with one trillion bacterial cells on the skin alone.
Interestingly, each person has their unique microbiome with which they live in symbiosis. Microorganisms find a habitat in the skin and a source of nutrients, in return, they protect the skin and the body from the penetration of harmful microorganisms, which can cause various diseases. In fact, the microbiome and the skin create an acidic layer (pH around 5) that prevents the growth of most harmful microorganisms, which is a finely tuned mechanism for avoiding infections and other pathogenic changes. Therefore, the microbiome is considered an important part of the skin’s barrier function and contributes to maintaining the skin in good condition. The diversity and balance between all species of microorganisms that make up the microbiome are key to its role.
The presence of sweat and sebaceous glands in the skin and the products they secrete determine which types of bacteria will dominate certain parts of the body. Species from the genera Propionibacterium and Staphylococcus dominate in sebaceous (oily) areas of the skin, such as the face and upper body, while the genera Corynebacteria, ß–Proteobacteria, and Staphylococcus dominate in moist areas such as the armpits, the inner side of the elbow, and the inner side of the knee. In dry skin areas, such as the forearm and buttocks, members of the genera ß–Proteobacteria, Corynebacteria, and Flavobacteriales can be found. The areas of the skin with the greatest bacterial diversity are dry regions, such as the skin of the forearm and legs.
The composition of the skin microbiome is variable, and the main factors influencing changes in its composition include gender, age, temperature, humidity, pH, availability of nutrients, host genetics, diseases and medications, hygiene habits (soaps and skin cleansing products with alkaline reactions can cause changes in the skin’s pH), the external environment, interactions with other microorganisms, and the host’s immune system.
Gender has a significant impact on the skin microbiome. Women have greater bacterial diversity within their microbiome compared to men. This is due to many differences between the female and male bodies, such as steroid production, skin thickness, sebaceous and sweat gland activity, the presence or absence of body hair, and skin pH.
The skin microbiome changes with age. It develops after birth during the first contact of the newborn with the external world, when colonization of the skin begins, and its composition is initially very simple. As we age, the skin microbiome becomes more diverse. Hormonal changes occur with puberty, leading to increased activity of sebaceous and sweat glands, and consequently to the development of so-called lipophilic bacteria, bacteria that inhabit oily areas of the skin. Additionally, with menopause, the skin loses lipids and elasticity, which also affects changes in the composition of the skin microbiome.
The axillary region (armpit) is the most important site for developing body odour. Due to the warm and moist environment, it is an ideal place for the growth of a large number of bacteria, and thus the creation of an unpleasant odour. The smell of axillary secretions becomes more intense as bacteria break them down. Body odours are associated with the dominance of “bad” bacteria in the axillary region. A new treatment called axillary bacteriotherapy is being developed worldwide, which is based on the transplantation of “good” bacteria, aiming to change the ratio of “bad” to “good” bacteria, of course in favour of the “good” ones. The transplantation results in an improvement in the body odor of the axillary areas.
In line with the role of the skin microbiome, the cosmetic industry, in its eternal quest for innovation, is developing cosmetic raw materials that are fermentation products and are likely to become a global trend of the future. The first steps have already been taken in South Korea. In this sense, the cosmetic industry is engaged in developing of probiotics, prebiotics, and postbiotics. Probiotics are considered to be live or inactive microorganisms (e.g., Lactobacillus casei, Lactobacillus acidophilus). Prebiotics are defined as nutrients necessary for the development of probiotics or the natural microbiome of the skin (e.g., niacinamide, minerals, thermal water, vitamins, oligosaccharides, natural oils, etc.). Postbiotics are defined as products or metabolic by-products secreted by live bacteria or released after the breakdown of bacterial cells (e.g., Bifida ferment lysate, Lactococcus ferment lysate, Bacillus coagulans ferment, etc.). In cosmetic products, prebiotics can contribute to the development of the skin’s natural microflora and increase microbiological activity, but very little is known about the effectiveness of topically applied prebiotics.
Preparations containing live microorganisms are extremely rare in the cosmetic raw material market. Such raw materials would, by definition, be considered probiotics and would likely prove to be highly valuable active components. However, the cosmetic industry has shown little interest in developing cosmetic probiotics, as it has proven challenging to ensure the vitality of live microorganisms in a cosmetic product. Without the ability to remain alive, the expected effects of the microorganisms on the skin are lost, and with them, customer trust. Additionally, ensuring health safety, which is a legal requirement and an ethical obligation of manufacturers to make their products safe for consumer health throughout the product’s lifespan, has proven difficult to achieve in such cases, despite the preservation process.
Moreover, the question of legal regulation of such a product remains open, as it could easily be classified as a borderline product between a cosmetic product and a drug due to unauthorized health claims that often accompany cosmetic products, usually out of ignorance or in an attempt to increase sales. All of the above complicates the marketing of cosmetic products with live microorganisms, and, likely, they will not become widespread anytime soon.
The cosmetic industry has chosen an alternative, safe approach and has shown interest in utilizing fermentation processes to obtain cosmetic ingredients rich in beneficial compounds such as proteins, ceramides, amino acids, and antioxidants. These raw materials are typically called “bioferments” and are considered postbiotics.
The main advantage of cosmetic ingredients obtained through fermentation is their compatibility with the skin, which tolerates and accepts them well. Fermentation enables the conversion of complex compounds into simpler ones. The simpler the compounds, the more easily they penetrate the skin, and thus their effectiveness at the site of action is greater.
Ferments from berries are characterized by their antioxidant properties, while ferments from red and black ginseng or tonka beans contribute to reducing visible signs of skin ageing. The last group includes ferments with moisturizing properties, such as aloe, seaweed, skim milk, and soy milk. These raw materials already have excellent skin moisturizing properties before fermentation, but the fermentation process significantly enhances this effect.
Conclusion
Fermentation is an efficient and interesting method of processing raw materials, but it requires further technological research, and the use of bioferments in the cosmetic industry is still minimal. However, it will likely find its enthusiasts among end consumers in the future.
