Probiotics: The anti-inflammatory effects of these microorganisms.

The skin is our primary defence against pathogens and plays a significant role as a barrier. When it feels under attack, an inflammatory response is triggered, mobilising a range of chemical mediators. Immune cells such as lymphocytes and leukocytes are the first to react and initiate the inflammatory response. Alert signals are then sent to other cells. The vasodilation and increased permeability of blood vessels in the affected area are then observed, leading to the appearance of several characteristic signs of skin damage: redness, swelling, irritation, itching...

The acne, the eczema, rosacea... These dermatoses all have one thing in common: their inflammatory component. To combat these diseases and improve the appearance of their skin, an increasing number of patients are turning to an alternative solution, complementary to their usual treatment: the intake of probiotics. Several studies have been conducted regarding the effectiveness of these microorganisms for alleviating skin inflammations and the results obtained are promising.

Firstly, we can mention Lactobacillus casei, probiotics that, when taken orally, exert an anti-inflammatory effect by modulating the immune activity of T CD4+ regulatory cells. These lymphocytes proliferate when they recognise certain pathogens presented by an antigen-presenting cell. Following this recognition, the T CD4+ activate other types of cells to participate in inflammatory mechanisms. This is why they are also referred to as helper T lymphocytes. Other studies have shown that the oral intake of other Lactobacillus type bacteria, such as Lactobacillus lactis and Lactobacillus fermentum can reduce skin inflammation.

In relation to inflammatory skin diseases specifically, several studies have been conducted and have also highlighted the benefits of orally taken probiotics for reducing inflammation.

• In the case of eczema: A study, spanning 16 weeks, involved 4538 patients suffering from atopic dermatitis randomly divided into two groups. The first group received a treatment with the probiotic Lactobacillus salivarius at a dose of 10,000 CFU/µg in maltodextrin twice a day, and the second group received a placebo, composed solely of maltodextrin. After four months, a significant reduction in skin inflammation was observed only in the group treated with the probiotic and no adverse effects were reported during the study.

• In the case of acne: A further study conducted over 12 weeks with 36 patients aged between 18 and 30 years, who were suffering from acne, demonstrated the benefits of a fermented milk containing 200 mg of lactoferrin along with probiotics derived from Lactobacillus bulgaricus and Streptococcus thermophilus. At the end of the study, the patients experienced a significant reduction (of 38.6%) in the number of their inflammatory lesions.

• In the case of rosacea: A clinical trial involving 57 patients with erythematous and papulopustular lesions was conducted. The participants were divided into two groups: one was treated with a standard topical therapy consisting of tetracyclines, corticosteroids, and retinoids, while the other was treated with the same therapy plus the oral administration of the probiotic strain Escherichia coli. After a month of follow-up, 32% of the patients in the probiotic group had recovered and 57% experienced a significant improvement in their skin inflammation, compared to 17% of the patients in the control group who had recovered and 39% who experienced a significant improvement in their skin inflammation.

In light of the rapid expansion of oral probiotics, numerous topical formulations have been proposed in cosmetics to enhance the balance of the skin's microbiota and promote immunological homeostasis. When applied topically, probiotics can notably reduce 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, involved in the photoaging of the skin. Moreover, this probiotic also has an effect on the levels of interleukin-8, pro-inflammatory cytokines that are upregulated during sun exposure. The application of Lactobacillus reuteri reduces their expression, which protects the skin.

The benefits of topical application of probiotics in cases of acne and inflammatory eczema have also been demonstrated. However, in relation to rosacea, they have not yet been proven.

• A double-blind, placebo-controlled study examined the effects of a lotion containing 5% of Vitreoscilla filiformis on 75 volunteers suffering from atopic dermatitis. Over a period of 30 days, participants applied either the lotion or a placebo, twice a day. The severity of the disease as well as skin inflammation were evaluated throughout the study. At the end of this trial, a significant reduction in inflammatory lesions was observed .

• In the case of acne: 70 patients suffering from acne participated in a recent study that focused on the effect of the bacterium Enterococcus faecalis, a species of the genus Lactobacillus acting against Cutibacterium acnes, the bacterium responsible for acne. For eight weeks, half of the individuals applied a lotion containing E. faecalis twice a day, while the other half applied a placebo. At the end of the study, scientists noted a decrease in the production of inflammatory mediators by C. acnes in the first group, as well as a significant reduction in the number and intensity of inflammatory lesions.

• GUENICHE A. & al. Effects of nonpathogenic gram-negative bacterium Vitreoscilla filiformis lysate on atopic dermatitis: a prospective, randomized, double-blind, placebo-controlled clinical study. The British Journal of Dermatology (2008).

• KANG S. & al. New perspectives on acne management: An update from the Global Alliance to Improve Outcomes in Acne Group. Journal of the American Academy of Dermatology (2009).

• CHO Y. & al. The impact of lactoferrin-enriched fermented milk on skin surface lipids and the clinical amelioration of acne vulgaris. Nutrition (2010).

• DRAGO L. & co. Alteration of faecal flora and clinical impact of L. salivarius LS01 in adults with atopic dermatitis. Journal of Clinical Gastroenterology (2012).

• STREMMEL W. & al. Dermatoses originating from the intestine significantly improved by oral application of Escherichia coli Nissle 1917. World Journal of Gastroenterology (2016).

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