ARTICLE 1: How and why does the skin become old?
What are the causes of the skin ageing process?
We consider that the first signs of skin ageing appear at 25 y.o. but the process ok skin ageing is launched at the birth, this is a natural and normal process and we need to live with it. We distinguish 2 kinds of factors having an impact on the skin ageing process: intrinsic factors which are inherent to the natural development of the skin and extrinsic factors that come from external environment.
1/ INTRINSIC FACTORS
We speak about intrinsic factors to describe a normal and chronological phenomenon that can be associated to the programmatic degeneration. Indeed, this is totally normal and natural that the functioning of our metabolism is modified with time and that skin faces the consequences. In fact, our cells’ metabolism is weakened with age. Cells lack energy and their repairing and regenerating actions are slowed down and less effective. This phenomenon is variable in function of all individuals, but we notice a clear acceleration of the skin ageing process for women with menopause.
2/ EXTRINSIC FACTORS
On the other hand, we speak about extrinsic factors to define all the extern causes that can have a negative impact on the good skin functioning. These factors are directly linked to our environment and also our habits. For instance, this is well known that UV rays alter our cells and their good functioning, accelerating this way the skin ageing process. This is also the case for cigarettes smoke, weather (extreme and quick temperatures changes), pollution, but also our alimentation, health practices and even strong emotions as stress, anxiety and fatigue. These external aggressions are factors of oxidative stress, they create oxidative wastes, instable and very reactive molecules that we call free radicals. These free radicals attack other cells components to be stabilized but by doing this they generate new instable molecules that irremediably lead to the vicious circle of cells oxidation. The balance between free radicals’ production and antioxidants defense is in danger. This is this oxidative phenomenon which is responsible for all the different ageing signs and in each skin layer at it will reinforce all the other skin ageing mechanisms.
What are the effects of the combination of extrinsic and intrinsic factors?
1/ NATURAL FUNCTIONING OF THE SKIN
We distinguish 3 layers composing the skin: the epidermis, which is the upper layer of the skin, the one in direct contact with the external environment and external reflection of our skin interne health. Then, the dermis located under the epidermis, this is a vascularized layer, that means « lively » and composed of different cells. And finally, the hypodermis layer links the skin to the whole organism, this is the deeper layer of the skin.
Each one of these layers is then divided in many sub-layers.
Let’s have a look on the epidermis composition as this is the layer where the skin ageing signs are the most visible. The epidermis is composed of many sub-layers from the most extern to the most intern: the corneous layer (= stratum corneum) composed of corneocytes which are dead cells that will progressively detached from the skin to be eliminated during the process of desquamation. The stratum lucidum, the stratum granulosum, the stratum spinosum and finally the basal layer which contains keratinocytes. Keratinocytes are cells that will progressively go up to the upper layer of the skin during the cell renewal process, to reach the upper layer as corneocytes.
The idea is now to understand how the different skin ageing factors play a role on the different layer of the skin and which are the effects of these modifications that we call physiopathologic.
2/ CUTANEOUS BARRIER & SKIN AGEING PROCESS
In this upper layer of the skin, skin ageing is measured by keratinocytes synthetizing less lipids (fatty substances), decreasing the cement between corneocytes and then the cells cohesion, while increasing the skin permeability. This leads to a dried and dehydrated skin.
Cornea layer touched by the skin ageing process:
3/ EPIDERMIS & SKIN AGEING
With time, the process of cell renewal is less and less frequent, which decreases also the desquamation process and make the skin tone dull.
By the time, the melanogenesis process is also disrupted: melanocytes – cells responsible for the skin coloration – do not function well anymore, which leads to the appearance of pigmentary spots and an uneven skin tone.
4/ DERMO-EPIDERMAL JUNCTION & SKIN AGEING
Between the epidermis and the dermis is located the Dermo-Epidermal Junction (DEJ), that binds these two layers of the skin. This is place of exchange between the cells, an essential place. Its structure is thin but very complex: it is composed of more than 20 macromolecules organized in thin layers. In the epidermis layer, it allows keratinocytes fixation at the dermis and on the side of the dermis, it keeps collagen fibers located in the upper layer of the dermis. It thus has several functions for the skin:
- A mechanical function: it maintains the dermis and the epidermis together thanks to the collagen network and laminin 5;
- A biological function: it acts as a filter to stop molecules but also to allow them to migrate from a layer to another during the immunological or inflammatory process. It thus has an essential role in the healing process of the skin.
Moreover, inside this DEJ, there is a protein which is naturally present in the skin and that we named Laminin 5. It acts as anchorage fiber that allows DEJ to resist to constraints, it is unique and essential as it guarantees structure and cutaneous cohesion. In addition, it carries biological signals which are crucial for the adhesion of keratinocytes. A young DEJ has many ripples (25 y.o.). With age we lose up to 50% of our Laminin 5, which is represented by a flat DEJ and a loss of ripples.
Concretely, the skin is slackening, and marks are accumulating. The skin becomes less resistant to environmental stress.
5/ DERMIS & SKIN AGEING
Meanwhile, in the dermis, the quantity of fibroplasts – which are located in the upper layer and which are essential to cells cohesion – decreases, as their ability to synthetize. The fivers are less numerous and of bad quality, which leads to a loss of firmness and elasticity, and the appearance of wrinkles and fine lines. There also is a vascularization anomaly that will create what we call “spider veins”.
6/ HYPODERMIS & SKIN AGEING
Finally, with age, we also lose the underlying fat located on the epidermis on some areas as forehead and cheeks. Paradoxically, we gain fat on areas as the mouth and the jaw, and this is precisely this unbalanced distribution that creates a loss of face volume and contours: fatty areas spread out and fat pads appear in separated structures.
This leads to a slackening of the skin.
What are the visible signs of all these physiopathologic changes?
1/ THE VISIBLE SIGNS OF SKIN AGEING
2/ THE DIFFERENT KINDS OF WRINKLES
3/ SKIN’S NEEDS IN FUNCTION OF EACH SIGNS
You now have a beautiful overview of the skin ageing process, let’s meet each other again in the future article to talk about preventive and treating solutions for these ageing signs.