Why is it important to take care of your skin microbiota? FILORGA tells you everything about skin bacteria.

Human skin is a complex organ whose main function is to protect it from external aggressions. The skin microbiota is one of the major players in this protective barrier function. In this article, we explain what it is composed of, how it lives, develops, and protects us, what can harm it, and how to care for it.

What is a microbiota?

A microbiota is a group of microorganisms (fungi, bacteria, viruses, yeasts, and also parasites like mites) that live in symbiosis with their host. The term symbiosis is important because it means that the microorganisms do no harm to the host they live on, and at the same time, the host does not seek to eliminate them. data-mce-fragment="1">The microbiota is present in all parts of the body in contact with the outside world. Humans can therefore be considered to have four different microbiotas:

• The digestive microbiota, present in the stomach and intestines. It is also called the microbiota or intestinal flora.
• The Skin Microbiota.
• The Respiratory Tract Microbiota present in the mouth, pharynx, and lungs.
• The Urogenital Microbiota.

Bacteria are the predominant microorganisms in humans. They are sometimes called commensals or normal flora, to clearly distinguish them from pathogenic bacteria. They keep our defense system constantly active, thus helping to strengthen our immunity.

To date, just over 1,000 different "good" bacteria have been identified.

What are the differences between skin flora and intestinal flora?

The flora in our intestines is the best-known human microbial and bacteriological complex. It never comes into contact with the air and performs several functions:

• The development and maturation of the immune system, essential for the body's defense against infections.
• Nutrient metabolism, including the fermentation of dietary fiber and the absorption of carbohydrates, proteins, and lipids.
• Protection against external pathogens.
• Maintaining the integrity of the digestive tract barrier, by strengthening the intestinal walls.
• Production of certain vitamins, such as B vitamins and vitamin K.
• The production of neurotransmitters, substances that are active in the brain and participate in the dialogue between the brain and the gut (it's not for nothing that the digestive tract is nicknamed the "second brain").

Interest in the gut microbiota has grown steadily over the past decade, and rightly so. Indeed, many diseases or physical conditions could be linked to an imbalance (the scientific term is dysbiosis) of this set of microorganisms. Its good health is highly dependent on what we eat, our physical activity, our stress levels, the quality and quantity of our sleep, and the medications (especially antibiotics) we take.

Unlike the intestinal flora,the skin flora is in direct contact with the external environment. It does not, of course, perform any digestive functions, but it is a key component of the skin's healthy barrier function. We will return to this point later in the article.

Finally, be aware that all microbiotas in the body are unique to each individual, which means that each person has unique needs.

Anatomy and Composition of the Skin Microbiota

Research into the structure and impact of the skin microbiota on skin health is a rapidly growing field, with new discoveries being made regularly.

Currently, it is known that a single cm2 of human skin containsup to several tens of millions of microorganisms. They are present on the surface of the skin, in the deeper layers of the epidermis, and in the dermis. data-mce-fragment="1">Skin bacteria belong to four main strains that vary depending on where they are found on the body. Indeed, sweat, sebum, pH, humidity, and skin temperature contribute to variable skin microenvironments, which influence the types of bacteria able to thrive in each ecosystem.

Four microenvironments have been described:

• A humid environment, with areas such as the armpits, the elbow crease, the space between the toes, or the inguinal fold.
• A sebaceous zone including, among others, the forehead or back.
• A dry area such as the front of the forearm or the upper buttocks.
• Areas not yet classified, such as those located in sweat glands or hair follicles.

The skin therefore has several "culture media" conducive to the growth of different microorganisms.

One ​​important point to remember is thatthe amount of skin water strongly influences the growth of microorganisms and differs considerably between the main areas described above. For example, dry, dehydrated skin inhibits the growth of commensal bacteria and promotes the development of pathogenic bacteriaStaphylococcus aureusresponsible for skin infections.

Keeping your skin well hydrated will maintain the normal composition of the microbiota, and at the same time, the skin's barrier function.

But the growth of pathogenic bacteria on the skin's surface isn't the only problem a damaged skin flora can cause.

What are the consequences of an unbalanced skin microbiota on the immune system?

To fully understand the impact of skin dysbiosis on health, it is important to understand the actions of the skin microbiota.

The main functions of the skin microbiota

The skin is constantly exposed to environmental stresses, and it is the skin microbiota that is the first to be exposed. It protects the entire body thanks to:

The barrier function

We briefly mentioned this above. The good bacteria present on the skin are a first barrier against external aggressions.They compete with invaders for food resources and space to reproduce. This phenomenon prevents the establishment and proliferation of opportunistic bacteria.

The skin microbiota acts on the skin's barrier effect by secreting enzymes and proteins that serve (among other things) toinhibit the multiplication of pathogens. For example, the bacteria Cutibacterium acnes helps make the skin hostile to "bad" bacteria like Staphylococcus aureus and data-mce-fragment="1">Streptococcus pyogenes and allows the proliferation of commensal bacteria such asStaphylococcus epidermidis.

Immune Function

Commensal and pathogenic bacteria are constantly interacting. If "bad" bacteria come into contact with "good" bacteria,the microbiota will resist in anticipation. Keratinocytes (the majority of cells in the superficial layer of the epidermis) constantly analyze the skin's condition. They are able to detect a future inflammatory problem before it even occurs and call on immune cells for reinforcement if the microbiota is unable to get rid of invaders on its own.

In association with the skin's immune system,the skin microbiota therefore helps contain many infections.

The different manifestations of skin dysbiosis

Skin dysbiosis is less serious than intestinal dysbiosis, but it still causes discomfort that can affect the quality of life of those affected. Two dermatological conditions have been attributed to it to date. Others are thought to exist (such as rosacea or psoriasis), but specialists need more scientific data to confirm this with certainty.

Atopic dermatitis

Atopic dermatitis is a chronic, inflammatory disorder that causes intense itching. It begins in childhood and is associated with asthma and allergic rhinitis. Although it is not the only cause, people with atopic dermatitis have an alteration of the skin barrier in the form of reduced microbial diversity compared to healthy people.

While the microbiota plays a secondary role in this condition (because it is not the cause), it nevertheless seems to promote the appearance of eczema flare-ups.

Acne

Acne is a chronic inflammatory disease that appears on areas of oily skin (face, neck, chest, and back). Although it particularly affects adolescents due to increased production of sex hormones, there are other forms that are found in adulthood.

In the case of acne, changes in the production andthe composition of sebum have a direct effect on the skin microbiota. It should be noted, however, that bacteria that thrive in the oiliest areas of the skin either promote or reduce the risk of inflammation. Here again, everything will depend on the physiology of the affected person.

How can the skin microbiota be preserved?

The epidermis is constantly renewing itself. This means that the skin microbiota, since it is located on the skin's surface, must do the same. Furthermore, frequent washing amplifies this need for regeneration, as cleansing the skin also eliminates protective bacteria.

We saw earlier that moisturizing your skin is a good way to preserve the health of the skin microbiota. As is maintaining optimal microbial and bacterial diversity (one species should not dominate another to avoid dysbiosis).

That's why skin experts recommend a few simple steps:

• Cleanse your skin just enough. Washing your skin too frequently can damage the surface hydrolipidic film and compromise the healthy development of the skin's microbial flora.
• Do not use cleaners with a pH that is too high. These products can damage the existing microbiota or promote the growth of certain harmful bacteria. For example, the bacteria Staphylococcus aureus, associated with atopic dermatitis, thrives at a pH above 7. Therefore, it's important to use products with a pH close to that of your skin, or around 5.5.
• Thoroughly dry the areas of the body where the skin is most wrinkled, data-mce-fragment="1"> because they are likely to retain moisture.

The skin therefore harbors a vast array of microorganisms that contribute to protection against invasive pathogens. Thus, any alteration of the skin microbiota can give rise to inflammation or lead to infections. It is therefore important to take maximum care not to upset the microbiota's bacteria by using suitable cosmetic products and not washing more than necessary.

Sources:

Di Domizio J, Pagnoni A, Huber M, Hohl D, Gilliet M. The skin microbiota: a colossus steps into the spotlight. Rev Med Suisse. 2016 Mar 30;12(512):660-4. French. PMID: 27172697.

Baldwin HE, Bhatia ND, Friedman A, Eng RM, Seite S. The Role of Cutaneous Microbiota Harmony in Maintaining a Functional Skin Barrier. J Drugs Dermatol. 2017 Jan 1;16(1):12-18. PMID: 28095528.