Side effects of topical application of probiotics?

The probiotics are microorganisms external to the body. According to the definition given by the World Health Organisation (WHO) and the Food and Agriculture Organization of the United Nations (FAO), probiotics are "live microorganisms which, when consumed in adequate amounts, have a health effect on the host". While they are primarily known for their therapeutic benefits and their ability to rebalance the gut microbiota, they can also be incorporated into cosmetic treatments where they provide several benefits for skin and hair health.

Probiotics have a broad spectrum of action and several studies have shown that they possess hydrating, healing, antioxidant, photo-protective, and anti-inflammatory properties. Moreover, they can be used to help alleviate the symptoms of certain dermatoses such as acne and eczema. Numerous studies have indeed highlighted that the topical application of probiotics can help to soothe sensitive skin and reduce redness and irritation.

Numerous studies have been conducted on the topical use of probiotics, and the majority have reported a lack of side effects. Indeed, the use of probiotics has not resulted in redness, irritation, itching, or swelling following their application. There is a fairly widespread fear that probiotics, being microorganisms, could disrupt the natural skin flora. At present, there is no scientific evidence to support this claim.

However, this does not prevent some researchers from considering that our current understanding of the microbiome is incomplete and that the use of such cosmetics is imprudent. Indeed, they believe that the application of live probiotics on the skin could potentially disrupt the skin microbiome and lead to the proliferation of "bad" bacteria. This is why, today, in cosmetics, most products claiming the presence of probiotics in their formula actually only contain "dormant" probiotics. These are microorganisms that are unable to grow but still retain their metabolic activity. More specifically, the molecules they contain remain active and can therefore be beneficial for the skin. The topical application of such probiotics then presents no danger to the skin.

Important : Even though probiotics are generally very well tolerated, including by those with sensitive skin, it is always advisable to perform a tolerance test the first time you use a new product.

• WALLEN-RUSSELL C. & WALLEN-RUSSELL S. Topical Probiotics Do Not Meet New Criteria for Effective Use Due to Insufficient Knowledge of Skin Microbiome. Cosmetics (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).