What are the benefits of cosmetic probiotics for the skin?

Probiotics are microorganisms external to the body that nonetheless play a significant role in maintaining various body functions. They are primarily used to boost the populations of microorganisms naturally present in different microbiomes (intestinal, skin, etc.). In doing so, probiotics prevent certain bacteria from overpowering others and disrupting the microbiome.

Primarily found in dietary supplements, probiotics are now making their way into the cosmetic field where they contribute to strengthening skin health. Generally obtained through successive fermentations, it's important to note that most probiotic-based skincare products do not actually contain live microorganisms. Indeed, as a precautionary principle, probiotics are most often incorporated in the form of "dormant" probiotics, meaning they are unable to grow but still retain their metabolic activity. More specifically, the molecules they contain remain active and can therefore be sources of benefits for the skin.

Most often, cosmetics containing probiotics target skin sagging. Indeed, most probiotics contain bioactive compounds in their extracellular vesicles that have effects on ageing. For example, lipopolysaccharides can be found in the extracellular vesicles of Gram-negative bacteria, while lipoteichoic acid is present in those of Gram-positive bacteria.

These chemical substances are notably capable ofinhibiting the activity of the matrix metalloproteinase MMP-1 and elastase. To remind, MMP-1 is a proteolytic enzyme responsible for the degradation of the extracellular matrix, providing a supportive role to the skin fibres. As for elastase, it is the enzyme responsible for the catalysis and loss of activity of elastin, a protein that is also essential for the skin's elasticity.

Furthermore, it has been demonstrated that Lactobacillus plantarum, a strain of probiotics also found in cosmetics, is capable ofincreasing the level of filaggrin mRNA expression, a molecule necessary for the homeostasis of the epidermis and the preservation of its skin barrier function. With age, the expression of filaggrin decreases, which contributes to skin fragility and laxity. These various properties make probiotics true allies of mature skin and explain why they are so prevalent in treatments intended for this type of skin.

Another key feature of probiotic-based cosmetics: their hydrating potential. Necessary for all skin types, good hydration is the foundation of a cosmetic routine and has numerous effects: improving skin texture, reducing feelings of discomfort and redness, preventing skin ageing...

The local application in vitro of Lactobacillus plantarum has recently been studied by a group of researchers. They found that treating epidermal cells with a preparation based on this probiotic led to anincrease in hyaluronic acid content, which has a strong moisturising power. The supposed mechanism of its action would be its ability to induce the production of cytokine IFN-γ in order to activate the NF-κB pathway through a synergistic effect with TNF-α. This results in the increase in the expression of hyaluronate synthase mRNA in fibroblasts, thus producing more hyaluronic acid. This enhances skin hydration and also helps to combat wrinkles.

The excessive attack of free radicals on biological tissues such as chromosomes, mitochondria, cell membranes, and connective tissues accelerates the ageing of the body and leads to several skin discomforts (pigmentation spots, more pronounced skin sagging...). Probiotics are interesting molecules to combat free radicals. Indeed, a study conducted on rats has shown that the topical application of Lactobacillus rhamnosus was able to reduce the content of free radicals in the skin cells.

Furthermore, several studies have shown that the combination of probiotics and well-known antioxidant molecules has synergistic effects. Indeed, the combination of β-nicotinamide mononucleotide (NMN) and lactic bacteria such as Lactobacillus fermentum helps to increase the levels of superoxide dismutase (SOD) and catalase in the skin, thereby enhancing its overall antioxidant capacity. Indeed, SOD and catalase are endogenous antioxidant enzymes that play a key role in protecting the skin from free radical attack and regulating oxidative stress.

Some probiotics also exhibit intriguing anti-inflammatory properties that can reduce the intensity of redness and alleviate skin irritation caused by exposure to UVB rays, which are responsible for sunburn. Indeed, the strain Lactobacillus reuteri has demonstrated its ability to inhibit the angiotensin-converting enzyme, which is involved in the photoaging of the skin. Moreover, this probiotic has a regulatory effect on the intracellular level of interleukin-8, a pro-inflammatory cytokine that is upregulated in cases of psoriasis , among other conditions.

Finally, probiotics are a good supplement to treatments prescribed by dermatologists in cases of acne and inflammatory eczema. Several studies have focused on the effects of these microorganisms in patients with either of these skin conditions and the results obtained have proven their effectiveness in reducing the severity of lesions.

In recent years, there has been an increase in the use of probiotics in cosmetics targeting pigmentation marks. Several researchers have investigated to better understand this effect of probiotics and have shown that certain strains could interfere with the expression of tyrosinase, an enzyme involved in the process of melanogenesis. More specifically, tyrosinase catalyses the transformation of tyrosine, an amino acid, into melanin, the pigment responsible for skin colour. Among the probiotics with anti-tyrosinase activity, we can notably mention Bifidobacterium and Lactobacillus plantarum, bacteria that have been the subject of several in vitro studies.

• GAULT M. & al. Pushing the Boundaries of Cosmetic Innovation: The Skin Microbiota and Probiotics Shield the Skin from UV-Induced Harm. Microorganisms (2021).

• YU J. & al. Application and mechanism of probiotics in skincare: A review. Journal of Cosmetic Dermatology (2022).

• QI H. Application of Probiotics and Metazoans in Cosmetics. The 2nd International Conference on Biological Engineering and Medical Science (2023).

• XU Z. & al. Applications of Probiotic Components in Cosmetics. Molecules (2023).