"Precious". This is another name we could give to the skin, it which protects us and informs us on a daily basis about our environment. She is the most personal, differentiates us from others, ne represents us, carries our scent, participates in interactions with others and shapes our physique according to the curves of the body. It is a reflection of our health and needs to be studied and understood in order to be able to best meet its expectations.
Its crucial importance and its complex physiological functioning inspired the exhibition "In my skin" presented until June 3 at the Musée de l'Homme in Paris. The latter makes it possible in particular to understand its functioning, its perplexity, its role or even the challenges for the future, all with the help of in-depth scientific work and studies. An exhibition to see to discover or rediscover the most relaxed organ in the human body and finally to discern the incredible biological and architectural complexity of that which accompanies us on a daily basis.
The skin, an organ with keen senses
To speak of it, we obviously use the term "organ". Term that tends to be forgotten about it, rarely knowing how to define it. However, no less is expected from this outer layer, which weighs nearly 4 kilos and connects the whole body through its many dandruff. We particularly know his epidermis, which is none other than the outer layer of the skin and whose thickness varies between 0.05 mm for the eyelid and 1.5 mm for the soles of the feet. The dermis takes place under the epidermis and is responsible for the firmness and elasticity of the skin. The tuning in of all these layers allows this vital organ to develop all of its senses. From touch to keen hearing, our skin feels everything and we know it if it needs it.
Who has never appreciated the softness of a caress on the arm or a good massage of the feet? This is in particular due to the large number of sensitive receptors present in the epidermis, mainly in the extremities, although other parts of the body also have them, but in smaller quantities. When solicited, these receptors trigger the secretion of neurotransmitters but also of the happiness hormone, namely endorphins or even oxytocins, responsible for attachment or even dopamine, a real energy booster. In summary then, a simple caress can relax and calm even the most restless and tense among us.
In all, nearly 600,000 sensory receptors and 200,000 thermoreceptors compete for the smallest part of our skin. Their presence informs the body about the outside world and allows our cognitive system to regulate our body temperature. They are also what allow us to assimilate the shape, the warmth or the firmness of an object; the sensory sensors being responsible for analyzing this information in order to transmit it to the brain which will then be in charge of recording it.
An organ directly connected to the brain
Whether it's cold, hot, windy, or rainy, the skin remains the most exposed organ and therefore the one that reacts accordingly. As a result, she may have goosebumps or suffer from prolonged violent exposure to the sun. Here again, it is the sensory sensors that send the brain all the information necessary for proper vital functioning. This is how it determines whether an object is smooth, rough, soft, hard, or hot or cold. The perception of pain also passes through these sensors and is transmitted to the brain along the nerves. This is how he learns which part of the body is damaged, depending on the intensity of the pain.
"The skin listens and speaks"
In good exterior facade, the skin is subjected, before the rest of the body, to the outside world. Attacks such as the sun, wind, water, temperature, viruses or pollution are immediately captured and processed via thermoreceptors which alert the brain. To protect itself and maintain the internal temperature of the body at 37 degrees, the thermoreceptors present in the skin send messages to the brain, which reacts accordingly. This is how we sweat, contract, get goosebumps, tan or get sunburned ...
In response to a cold snap, for example, the body reacts and defends itself by contracting small muscles on the skin that make the hairs stand on end. We call it goosebumps. Unfortunately, this muscular mechanism is no longer very effective today because, unlike our ancestors, most of our hair has disappeared. On the other hand, at the time it allowed body heat to be retained by acting as an insulating layer.
But it is the same with the harmful rays of the sun, that is to say UVA and UVB from which it is necessary to protect oneself. These former penetrate more easily than UVB rays and reach the dermis, where the proteins of collagen and elastin are housed. Once altered by radiation, the latter can unfortunately no longer ensure elasticity and cause skin aging. Faced with UVB, the skin also reacts by stimulating the production of melanin and also of keratinocytes which will thicken the stratum corneum to make it less permeable to radiation.
When we all consider ourselves to be dealing with a simple uniform surface, it really is not. We think in particular of the different layers mentioned above, but also of the receptors, the hairs but also the blood vessels and glands, among others, which together, support this outer layer as well as the whole body. What to talk about a complex architecture that accentuates between microbiota and microbiome.
A multitude of microorganisms
Beyond its typical cells, the skin is also inhabited by many invisible microorganisms which participate in its protection on a daily basis. We then speak of the microbiota, not to be confused with the microbiome which defines all the genes present in the microbiota. This is actually a set of bacteria, viruses, fungus or even mites that live in harmony on the surface of the body and synthesize, via their metabolic activity, all the products necessary for the good health of this surface. It is when the balance between these different species is upset, allowing harmful bacteria to take hold, that the skin is abused. Unique to each of us, this microbiota defines us as an identity card might.
The microbiota, a microflora necessary for the well-being of the skin
There is nothing negative about the presence of this collection of bacteria on the surface of the skin. As we mentioned above and as the duly cited exhibition presents, this bacterial flora communicates between its different species via chemical messages. She is then fully aware of the dangers and strives every day to ensure stability. To survive, this microbiota feeds on the proteins and lipids contained in the skin and in return secretes a film, the famous “hydrolipidic film” which protects it from outside invaders.
Here, in the midst of this flora far from being frozen, we find all kinds of species, mites and microscopic fungi that colonize the skin when conditions are favorable for their reproduction. Each patch of the latter contains nearly a billion bacteria and a hundred times more bacterial genes. No need to wince at their presence since it is totally normal and justified. In addition, mites for example feed on our dead skin. Bacteria secrete a hydrating barrier that prevents the skin from cracking or drying out. In rare cases, however, it is possible that fertilizing some of these species will cause itching or minor allergies. At the base of the eyebrow or eyelashes, for example, there is a small mite called demodex folliculorum, the proliferation of which can sometimes cause skin infections.
A scientific issue
Understanding the skin is above all being able to offer it a tailor-made future between adapted care and scientific breakthroughs. The presence of all this still misunderstood flora or of this complex architecture still needs to be elucidated in order to derive all the answers necessary for scientific and medical developments in the future.
A first step in skin reconstruction
There have already been many advances, particularly in the case of major burns. At this stage, it is now possible to reconstruct simplified skins which have moreover already allowed the transfer of grafts adapted to the latter. Cell banks have been created in this context in order to be able to respond to scientific research.
But for the researchers, it is now a question of going even further, using, among other things, new techniques including 3D bioprinting which could be used to print skin fragments necessary for skin reconstruction! These same researchers are also talking about understanding the very complex microbiota so that they can finally use it to keep the skin in shape over time. So many mysteries still unanswered that open a very wide field to the scientific challenges of the future.
"In my skin" exhibition at the Musée de l'Homme. From March 13 to June 3, 2019.