The body is in constant renewal throughout life. Almost all organs, except neurons and cardiac cells, are completely renewed several times, at a different frequency, from one week for the liver to 4 months for the bones. The skin, which is an organ, also renews itself, thanks to the regeneration of its cells.

Cellular renewal refers to the ability of cells to reproduce, that is, to produce genetically identical cells that take the place of other cells. At the end of their life, these cells eliminate themselves. Skin cell renewal is the process that leads to the elimination, every day, of thousands of dead cells, replaced by new ones. The right frequency of cell renewal, neither too slow nor too fast, is essential to maintaining a good barrier function, for radiant, uniform, smooth and full of energy skin.

Where does skin cell renewal take place?

The epidermis, the surface layer of the skin, is a bit like a game of Tetris. It's a kind of wall made up of bricks, keratinocytes, which are cells that constantly rise towards the surface. These brick cells are born in the basal layer, at the bottom of the epidermis and gradually migrate towards the stratum corneum, the most superficial layer of the epidermis.

What is the mechanism of skin cell renewal?

As they rise from the deep -basal- layer of the epidermis towards the surface, keratinocytes undergo different mutations. This is cell differentiation.

• In the reservoirs of the basal layer are the keratinocyte stem cells. They divide to give birth to a daughter stem cell - which will replace it in the basal layer to divide later - and another keratinocyte, almost cubic and equipped with a nucleus, which, pushed upwards by the new cells , begins its differentiation by going up to the upper floor. This is cell proliferation.

• The spinous layer is the thickest of the epidermis, made up of 4 or 5 layers of keratinocytes. The latter, almost polyhedral in shape and swollen with water, weld together thanks to desmosomes and hydrophilic and hydrophobic substances. As they go up, they become loaded with keratin and melanin.

• It is in the granular layer that the main transformation, called cell differentiation, takes place. The granular layer is a transition zone that separates the living epidermal layers from the so-called “dead” layers of the stratum corneum. Keratinocytes are completely remodeled to become corneocytes. They gradually lose their nucleus and their plasma membrane to give way to a rigid and insoluble envelope, the horny envelope. Furthermore, one of the differentiation markers, filaggrin, is transformed into free amino acids which constitute the “natural moisturizing factors” of the stratum corneum.

• Arriving at the surface, in the stratum corneum (or stratum corneum), the corneocytes are flat and filled with keratin, and agglutinate in a stack of cellular lamellae welded together thanks to the intercellular cement made of lipids, to constitute the skin barrier. They end up detaching thanks to enzymes which will release the snaps which hold the corneocytes together, the desmosomes. It's flaking. All this happens slowly and almost invisible. Without realizing it, we lose around four grams of skin per day.

Cellular renewal: how long?

Skin cell turnover is a bit like snake shedding, except we don't let our skin shed in one piece in one day. Between the birth of a cell and its migration to the stratum corneum, there is normally 21 to 28 days. Keratinocytes spend very little time in the lower layers but remain for about 14 days in the stratum corneum. But the frequency of skin cell turnover naturally slows with age. The cells become more “lazy” and take much longer to migrate over the years. From the age of 50, the speed of cell renewal decreases by almost 40%. This is why we seek to “stimulate” cell renewal with specific anti-aging treatments.

What are the factors that act on cell renewal?

In a healthy epidermis, the quantity of cells eliminated from the surface is compensated by the production of new keratinocytes in an identical proportion. But sometimes the process goes awry, with proliferation slowed or accelerated.

• Accelerated renewal, healing and psoriasis When our skin is injured or infected, cell renewal intensifies in order to repair the injury - this is the healing process - or fight infection with new cells. This acceleration can reach seven times the rate of normal cellular reproduction, or 3-4 days. Chronic inflammatory skin disease, considered an autoimmune disease, psoriasis manifests itself by accelerated cell renewal in the affected area (knees, elbows, scalp, etc.), which no longer stops. New cells are born and rise to the surface at a faster rate than that of sloughing. Dead cells accumulate on the surface of the skin and eventually form plaques, “scales”. These plaques come off like scales, while underneath the cells, which jostle and pile up, create painful lesions that can bleed.

• Slowed renewal: stress, obesity, tobacco, pollution, UV rays, and age slow down skin renewal. The skin struggles to slough off, dead cells accumulate on the surface because the bonds that hold the skin cells together (the desmosomes) do not detach as they should. These form a film that thickens the skin and makes the complexion dull and the skin rough. This accumulation also causes a loss of cohesion of the corneocytes, which are no longer able to effectively regulate the evaporation of water, resulting in progressive dehydration which leads to the premature appearance of fine lines.

How to renew skin cells?

To “boost” cell renewal, there are several possibilities, which can be combined.

Exfoliate

Exfoliating regularly – once or twice a week depending on skin type – is the easiest way. This gives the skin a little help to get rid of its dead cells. The message given to the skin that the dead cells are gone, encourages the epidermis to produce new ones. You can choose a mechanical scrub which eliminates "dead skin" by the friction of grains, stones or shells of crushed fruits and nuts, salt, sugar etc. Practical on the body, but sometimes too abrasive on the face, this type of Exfoliants can cause skin irritation, depending on the force applied and the type of grains. In fact, we would need very fine and round particles, and not angular (even if they are micro-angles).

This is why we often recommend – and even more so for sensitive skin – so-called chemical or enzymatic exfoliants, which produce uniform exfoliation by chemical degradation of cells. There are two types :

• Acids: these are the famous AHA for Alpha Hydroxy Acids (glycolic acid, malic acid, mandelic acid), BHA for Beta hydroxy acids (salicylic acid), or PHA for Poly Hydroxy Acids (gluconolactone)... They produce exfoliation. more or less gentle: glycolic acid, smaller, penetrates deeper, is ultra effective but can be irritating, while PHAs are much gentler but require more time to act. And promote skin renewal, unclogging of pores, softer skin texture, better hydration…

• Enzymes: these enzymes (generally plant-based) “nibble” at the links between dead cells – the desmosomes – to detach them without damaging living cells or irritating the skin.

Choosing the right assets

In addition to fruit acids, there are certain active ingredients known to boost cell renewal. This is the case of retinol, a powerful anti-aging active ingredient, one of the benefits of which is to promote skin renewal through its keratolytic (desquamanting) effect, but which can be irritating, particularly for sensitive skin. Hence the search for so-called “retinol like” molecules of plant origin, which ensure the actions without the disadvantages, such as bakuchiol, harungana, sea christe, paillon bean, pelargonium essential oil. New, micronized mother-of-pearl powder introduced into facial care, has scientifically demonstrated that by inducing the expression of certain key proteins such as filaggrin, it stimulates the migration of keratinocytes towards the surface of the epidermis to ensure the good “turnover” of cell renewal which guarantees repair and regeneration of the barrier and the epidermis to maintain stronger, healthy and radiant skin: skin in full health. A valuable action to which is added an anti-radical power and stimulation of the production of type I collagen fibers to preserve the density and youthfulness of the skin.

Eat well

Diet also has an influence on cell renewal. Favor foods rich in vitamin A and beta-carotene. Vitamin A is mainly found in ingredients of animal origin (eggs, butter, offal, liver). While beta-carotene, a precursor of this same vitamin but also a strong antioxidant, is present in orange fruits and vegetables (carrots, sweet potatoes, melon, pepper, leafy green vegetables). Foods rich in vitamin C (citrus fruits, kiwi, peppers) are also useful for good cell regeneration. In the BLUE SKINCARE NACRE ÉCLAT Range, when the skin is tired and lacking radiance, we advise you to complete your beautiful skin routine by using the Skin Perfecting Food Supplement. Ultra concentrated in active mother-of-pearl, it also contains a complex of pre & probiotics to rebalance the intestinal microbiota, hyaluronic acid to maintain the hydration and elasticity of the skin. Rich in vitamin C and zinc, it is an anti-oxidant and contributes to the normal formation of collagen for plumper skin.

Have a good nighttime routine

It is at night that cell renewal reaches its peak. No longer having to defend themselves from daytime attacks, skin cells repair and regenerate between 11 p.m. and 2 a.m. It is even around 1 a.m. that the skin's activity is maximum, multiplying cell renewal by three compared to the same mechanism at 1 a.m. in the afternoon. It is therefore time to give your skin treatment that will help this renewal by using a specific treatment such as the NACRE ÉCLAT New Skin Serum from the BLUE SKINCARE brand, ultra concentrated in active mother-of-pearl powder, NACR-45®. If the skin is dehydrated, we correct it. Because this skin renewal process requires water. Good hydration, through treatments but also by drinking 1.5 liters of water per day, is therefore essential to support cell regeneration. Obviously, it is essential to sleep well, sleeping 7 hours if possible to give the skin time to regenerate.