How do consumed probiotics act on the skin?

The term "microbiota" refers to the collection of microorganisms living in a specific environment. This includes viruses, bacteria, and yeasts. There are several types of microbiota in the human body, but the gut microbiota is the most populated among them. This complex ecosystem is closely linked to other microbiotas, particularly the skin flora. Indeed, several studies have shown that an imbalance in the populations of gut microorganisms can lead to a state of inflammation not only in the intestines, but also in distant organs, including the skin. It has also been established that disturbances in the gut microbiota can contribute to the development of certain skin diseases such as acne, eczema, psoriasis and rosacea. It appears that the immune system is the mediator of this connection between the skin and the gut.

The gut-skin axis suggests a relationship in which the immune properties of the gut microbiota can also influence skin health. For instance, it has been shown that propionate synthesised by the gut bacterium Propionibacterium, has an anti-microbial effect against certain skin pathogens such as Staphylococcus aureus. Given the link between the gut and skin microbiota, the positive modulation of the gut flora through oral probiotics can be considered as a potential clinical approach to prevent skin photoaging, reduce its inflammation and make it more radiant.

Numerous studies have been conducted on the benefits of oral probiotics for skin care, and the results are, for the most part, very promising.

• Probiotics protect the skin from oxidative stress.

  The excessive generation of free radicals in skin cells following exposure to UV rays, pollution or tobacco is the primary cause of its premature ageing. Antioxidants, molecules capable of neutralising radicals, prevent these oxidative stress phenomena and protect the constituents of the skin. It has been shown that certain strains of probiotics such as Lactobacillus acidophilus and Limosilactobacillus fermentum have antioxidant properties when taken orally. Indeed, it appears that these probiotics may increase cellular concentrations of glutathione, a molecule involved in the elimination of reactive oxygen species, and the activity of superoxide dismutase, a powerful antioxidant enzyme.

• The probiotics have an anti-inflammatory effect.

  Inflammation of the skin can lead to a malfunction of its barrier function, redness, blemishes, or even significant water loss. Various strains of probiotics have demonstrated their anti-inflammatory potential in studies conducted orally. The Lactobacillus casei in particular are capable of modulating the immune activity of T CD4+ regulatory cells. These lymphocytes proliferate when they recognise certain pathogens presented by an antigen-presenting cell. They then activate other cells which in turn participate in inflammatory mechanisms. Other Lactobacillus type bacteria, such as Lactobacillus lactis and Lactobacillus fermentum, can also reduce skin inflammation.

  Furthermore, research has shown that oral supplementation with Bifidobacterium breve is effective in reducing the content of interleukin-1β (IL-1β) in the skin. This pro-inflammatory cytokine, which is synthesised particularly following prolonged exposure to UV rays, plays a role in the onset of redness, irritation, swelling and other signs indicating skin inflammation. Finally, oral intake of probiotics derived from Staphylococcus epidermidis can reduce levels of interleukin-6, another pro-inflammatory cytokine in skin cells by using SCFA receptors. Expressed only in the gut, these play a significant role in modulating inflammatory and immune responses at various levels of the organism;

• Probiotics alleviate symptoms associated with certain skin diseases.

  The oral intake of probiotics has also proven to be very useful in combating certain inflammatory skin conditions. The strain Lactobacillus salivarius in particular demonstrated its effectiveness in a study to alleviate inflammatory symptoms in over 2000 patients suffering from atopic dermatitis. Furthermore, no side effects were reported. We can also mention probiotics based on Escherichia coli. Studies conducted on this bacterial strain have shown its anti-inflammatory potential and its action on papulopustular rosacea. Finally, oral supplementation for 12 weeks in 36 patients suffering from acne of Lactobacillus bulgaricus and Streptococcus thermophilus has shown the effectiveness of these probiotics in alleviating inflammatory acne lesions.

• Probiotics assist in delaying skin ageing.

  Oral probiotics are highly praised for their preventive action on signs of ageing. Indeed, certain strains such as Lactobacillus buchneri have demonstrated their effectiveness in increasing the production of type I procollagen. This is an essential precursor of collagen, a structural protein playing a significant role in maintaining skin elasticity. Moreover, this microorganism can also inhibit the synthesis of elastase, the enzyme responsible for the degradation of elastin, another protein contributing to preserving the structure of the skin.

  It has also been demonstrated that probiotics derived from Lactobacillus acidophilus when administered orally, could reduce the mRNA level of certain matrix metalloproteinases by damaging the AP-1 loop in the skin. Matrix metalloproteinases are proteolytic enzymes responsible for the degradation of the extracellular matrix, providing a supportive role to the skin's fibres. Furthermore, Lactobacillus acidophilus is also believed to act by increasing the level of procollagen in the dermis, which would also contribute to preventing skin sagging and the appearance of wrinkles.

• LAYDEN B. & al. The Function of Short Chain Fatty Acid Receptors in Intestinal Physiology and Pathophysiology. Comprehensive Physiology (2018).

• NOWICKA D. & al. Microbiome and Probiotics in Acne Vulgaris—A Narrative Review. Life (2022).

• REN F. & al. The Role of Probiotics in Skin Health and Related Gut-Skin Axis: A Review. Nutrients (2023).