The skin serves as the first line of interaction with the external environment and as a defence mechanism against the physical, chemical, or biological stresses and challenges it encounters. The skin microbiota plays a key role in these interactions and defence functions. Formerly known as "skin flora", it colonises every square centimetre of the skin. Its role is fundamental to both skin health and the overall well-being of the body. What are the factors that influence its composition, and what disrupts its functions?
The skin microbiota, an ally in skin protection
A major role in skin barrier function
The skin acts as a protective barrier between the body and the environment, serving as a physical and chemical barrier that prevents pathogens and toxins from entering.
The skin’s microbiota plays a major role in maintaining the integrity and functionality of this barrier, which protects life. Amongst its properties, the skin’s microbiota:
- constitutes a physical barrier against pathogens’ invasion, establishing with them an eubiotic equilibrium in terms of food and space;
- produces antimicrobial substances, thus ensuring a chemical barrier;
- participates in the skin protective biofilm structuration;
- participates actively in the normal and constant process of the skin’s desquamation and self-repair.
Skin Microbiota and immunity: A constant dialogue
The skin’s microorganisms play a role educating the mucosal immune system, similar to the identified interactions between the gut microbiota and the intestinal mucosal barrier. As a result, the skin’s microbiota maintains a continuous dialogue with the mucosal-associated immune system (MAIS). This communication favours an appropriate inflammatory response in case of injury and an effective wound healing.
An evolving microbiota, that adapts but is vulnerable
The skin microbiota is influenced by numerous factors
Internal factors that regulate the skin microbiota’s composition include:
- the balance of the gut microbiota (the gut-skin axis) and its connections to diet and stress (the gut-brain-skin axis);
- Medications, such as antibiotics and corticosteroids;
- Gender and hormonal balance.
Its balance is also influenced by external factors. Being in direct contact with the external environment, the skin is subject to:
- Climate variations (temperature, ambient humidity, UV exposure, hygrometry);
- Pollution: a different skin microbiota has been observed in urban environments compared to more rural ones;
- Cleansings and the use of cosmetic or body hygiene products (soaps, lotions, creams, deodorant;
- The types of clothing worn, which can affect the acid and secretion production of the skin.
Alteration causes of the skin microbiota
The skin microbiota has the ability to self-regenerate and stabilise. Despite this remarkable resilience, this ability can be altered. An excessive frequency of washing, or the repetitive application of non-adapted products, antibacterial agents, antibiotics, or antifungals can profoundly degrade its integrity. Consequences of this degradation include the destruction and non-renewal of the hydrolipidic biofilm, increased desquamation, local inflammation, and the proliferation of certain drug-resistant strains responsible for fungal infections. These are all signs of skin microbiota dysbiosis.
A skin dybiosis, if it persists, can trigger or perpetuate certain skin diseases. Although it is always challenging to determine whether skin microbiota dysbiosis is the cause or consequence of a skin condition, it is clear that a state of dysbiosis will only exacerbate the symptoms.
The « Gut-Skin Axis »
The gut microbiota has a close bidirectional relationship with all other microbiotas. Therefore, it plays a role in the development or maintenance of dermatological pathologies.
Like the gut-brain axis, which is now extensively studied, the "gut-skin axis", and more specifically the "gut-brain-skin axis," has become a topic of scientific interest. (Arck et al. 2010). This axis has been identified through the study of skin conditions such as atopic dermatitis, eczema, acne, seborrheic dermatitis, psoriasis, and rosacea. Cutaneous homeostasis is now recognized as strongly linked to gastrointestinal health and nervous balance. (De Pessemier et al. 2021).
Both the epidermis and intestinal epithelium functionally and structurally share many similarities. (De Pessemier et al. 2021). This discovery has paved the way for new therapeutic strategies, such as the study of the impact of oral probiotics and/or prebiotics on improving certain skin conditions. See our article on how to preserve the skin microbiota.
"Why preserve the skin microbiota?" in a few words...
The stability of the skin microbiota results from complex interactions between genetic susceptibility, the immune system balance, lifestyle, exposure to environmental factors, and maintaining close links with the gut-brain axis. This stability is a direct consequence of good intestinal and nervous health.
The skin microbiota plays a vital role in constructing and maintaining an effective skin protective barrier. It is also crucial for educating and regulating immune responses. Preserving it is essential to prevent skin inflammation and the development or exacerbation of dermatological pathologies. Numerous studies are currently underway to assess the real impact of skin microbiota disruptors, contributing to the development of products that respect our skin microbiota (See our article on the influence of skin microbiota on skin health)
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Clarke, G.; Stilling, R.M.; Kennedy, P.J.; Stanton, C.; Cryan, J.F.; Dinan, T.G. Minireview: Gut microbiota: the neglected endocrine organ. Mol. Endocrinol. 2014, 28, 1221–1238
De Pessemier B, Grine L, Debaere M, Maes A, Paetzold B, Callewaert C. Gut-Skin Axis: Current Knowledge of the Interrelationship between Microbial Dysbiosis and Skin Conditions. Microorganisms. 2021;9(2):353. Published 2021 Feb 11. doi:10.3390/microorganisms9020353
Ellis SR, Nguyen M, Vaughn AR, et al. The Skin and Gut Microbiome and Its Role in Common Dermatologic Conditions. Microorganisms. 2019;7(11):550. Published 2019 Nov 11. doi:10.3390/microorganisms7110550
Lee SY, Lee E, Park YM, Hong SJ. Microbiome in the Gut-Skin Axis in Atopic Dermatitis. Allergy Asthma Immunol Res. 2018;10(4):354-362. doi:10.4168/aair.2018.10.4.354
O’Neill C. A., Monteleone G., McLaughlin J. T., Paus R. (2016). The gut-skin axis in health and disease: a paradigm with therapeutic implications. Bioessays 38 1167–1176. 10.1002/bies.201600008
Salem I, Ramser A, Isham N, Ghannoum MA. The Gut Microbiome as a Major Regulator of the Gut-Skin Axis. Front Microbiol. 2018;9:1459. Published 2018 Jul 10. doi:10.3389/fmicb.2018.01459