The human microbiota refers to all the microorganisms (viruses, bacteria and fungi) living on our entire body. Indeed, we have more than 100,000 billion bacteria including more than 500 different species. But rest assured, each of these microorganisms are an integral part of who we are and who we are. They are naturally present in our body, live in total symbiosis and are essential for the proper functioning of it.  

This microbiota is distributed over the different areas where the human body is in contact with the outside world: the digestive tract (mouth, esophagus, stomach, digestive tract), the respiratory tract, the urogenital system and the skin. Each of them has specific characteristics such as temperature, pH, fat and protein content. All this constitutes a defined environment that will be specifically favorable to certain species. Thus, from one area to another we will not find quantitatively and qualitatively the same bacteria, viruses and fungi.  

Any dysbiosis or imbalance of this environment leads to the proliferation of external pathogens. This leads to various consequences such as dermatitis, vaginal mycosis or digestive disorders.

Concerning more specifically the skin microbiota, how is the skin flora formed and evolved ?

It comes mainly from the mother. Indeed, at the prenatal stage our skin is sterile, it is during our birth that it settles. Either by direct contact with its vaginal flora during a vaginal delivery or by its digestive flora if caesarean section.    

It evolves and diversifies thereafter throughout our lives. Intrinsically, it will be in greater quantity during puberty because of the hormonal peak and it will naturally decrease during our aging. But also extrinsically via our daily environment (our place of residence, our transport, our activities, our state of health etc.).

How to differentiate good from bad skin bacteria?

It is important to dissociate the residential and transient skin flora. Indeed, the composition of these microbial communities, their living environments and their implications are different.

Resident skin flora

It corresponds to the set of microorganisms implanted for life and stably on our skin (on its surface, in each undercoat, in the glands and in the hair follicles). They are not pathogenic, on the contrary, their presence is essential for the proper functioning of the skin because they mainly participate in its defense against the different bacteria, viruses and fungi of the environment but also against UV radiation or pollution for example.

It consists of different bacteria whose three most predominant genera are Straphylococcus, Propionibacterium and Cornynebacterium. There are also yeasts of the genus Malassezia, mites of the genus Dermodex and some viruses.

Transient skin flora

Unlike the previous one, this one consists of microorganisms from the external environment, contaminated environments or other flora (digestive or urogenital).

Not being adapted to the skin environment, their residence times on the surface of the skin is short. This flora is therefore unstable, it is easily transmitted from individual to individual and generally varies during the day according to the activities carried out or our external environment.

However, if this environment were to change (change in pH, temperature, excess sebum, a wound etc.) it could become favorable to them. They will be able to compete with the resident skin flora, colonize the skin and create different skin pathologies such as acne or psoriasis.  

It consists mainly of bacteria of the genus Pseudomonas, Enterococci, Staphylococcus, Streptococcus and Bacillus but also yeast of the genus Candida.

Do we have the same skin bacteria?

What is intra-individual variability?

Intra-individual variability means that over our entire body surface we do not have the same bacteria, viruses and fungi or at least depending on the area, in different quantities. This distribution is specific to each one and constitutes our "identity card".

Remember, each microorganism has its own specific environment. The environment of the skin flora is defined by body temperature, pH (acidity of the skin), sebum, sweat and protein levels, hairiness, light received, etc.
On these parameters, we can therefore dissociate three skin areas where the composition and distribution of these microorganisms will be different :

• Wet areas : nostrils, armpits, elbow creases... These are areas rich in hair follicles and/ or sweat glands (responsible for sweat secretion) 
• Oily areas : forehead, ears, back... These are the areas most in contact with the external environment and are the richest in sebaceous glands.
• Dry areas : arms, hand... These are the areas where you have the least.

What is inter-individual variability?

As described earlier, we are unique. Thus, from one individual to another we do not have the same skin flora.

 This is defined by our bodily identity according to:

• Genetic predispositions
• Sex (men would have a higher microbial density than women because they have more sebaceous and sweat glands but also a greater hair)
• Age (birth, puberty, old age)
• The production of sebum and sweat (the distribution and activity of the glands are different depending on the individual)
• The immune system
• Hormone production
• The thickness of the skin

But also by some external parameters such as :

• The environment (climate variability, geographical location, etc.)
• Lifestyle (hygiene)
• The use of cosmetics
• Taking medication

Do black, matte and mixed skins have a different skin flora?

Black, matte and mixed skins have different characteristics from Caucasian skins. Indeed, the skin of their faces are more acidic, more dehydrated and more oily. They renew themselves and remove their dead cells more slowly which creates an irregular skin texture.

All this is favorable to the proliferation of bacteria. For example, the fact that the skin is oilier, they have more nutrients to feed themselves and will be able to develop more easily. The presence of dilated pores and a relief of non-smooth skin give them the opportunity to nest and consequently increase their number. All these characteristics suggest that black, matte and mixed skin has more bacteria on their skin than Caucasian skin.  

OYA, we know that some of you have already thought about consuming probiotics in the form of tablets or eggs to maintain or replenish your digestive or vaginal flora. Have you never taken one ? Maybe you've used intimate washing gels or eaten bifidus-based yogurts ? Anyway, today it is time to take care of your skin flora because well-protected skin and skin that ages much more slowly.