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

Cell 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, each 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 energetic skin.

Where does skin cell renewal take place?

The epidermis, the superficial layer of the skin, is a bit like a Tetris game. It is a kind of wall made of bricks, keratinocytes, which are cells that are constantly rising 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 move up from the deep -basal- layer of the epidermis towards the surface, the keratinocytes undergo different mutations. This is cellular differentiation.

• In the reservoirs of the basal layer are the keratinocyte stem cells. They divide to give rise to a daughter stem cell - which will replace it in the basal layer to divide later - and another keratinocyte, almost cubic and with a nucleus, which, pushed upwards by the new cells, begins its differentiation by rising to the upper level. 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 to each other thanks to desmosomes and hydrophilic and hydrophobic substances. As they rise, they become loaded with keratin and melanin.

• The main transformation, called cellular differentiation, takes place in the granular layer. The granular layer is a transition zone that separates the living epidermal layers from the so-called "dead" layers of the horny layer. The keratinocytes are completely remodeled to become corneocytes. They gradually lose their nucleus and plasma membrane to make way for a rigid and insoluble envelope, the horny envelope. In addition, one of the differentiation markers, filaggrin, is transformed into free amino acids that constitute the "natural moisturizing factors" of the horny layer.

• Once they reach the surface, in the horny layer (or stratum corneum), the corneocytes are flat and filled with keratin, and clump together in a stack of cellular lamellae welded together by the intercellular cement made of lipids, to form the skin barrier. They eventually detach themselves thanks to enzymes that will break the snap fasteners that hold the corneocytes together, the desmosomes. This is desquamation. All this happens slowly and almost invisibly. Without realizing it, we lose about four grams of skin per day.

Cell renewal: how long?

Skin cell renewal is a bit like snakes 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, 21 to 28 days normally pass. Keratinocytes spend very little time in the lower layers but remain in the stratum corneum for about 14 days. But the frequency of skin cell renewal naturally slows down with age. Cells become "lazier" 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 affect cell renewal?

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

• 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 to fight the infection with new cells. This acceleration can reach seven times the rate of normal cell reproduction, or 3-4 days. A chronic inflammatory skin disease, considered an autoimmune disease, psoriasis is manifested 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 desquamation. Dead cells accumulate on the surface of the skin and end up forming plaques, the "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 flake, dead cells accumulate on the surface because the bonds that hold skin cells together (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, hence progressive dehydration that 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 your skin type – is the easiest way. This gives your skin a little boost to get rid of its dead cells. By sending the message to the skin that the dead cells have gone, the epidermis is encouraged to produce new ones. You can choose a mechanical scrub that removes “dead skin” by rubbing grains, pits or shells of crushed fruits and nuts, salt, sugar, etc. Practical on the body, but sometimes too abrasive on the face, this type of exfoliant can cause skin irritation, depending on the force applied and the type of grains. In fact, you need very fine and round particles, not angular ones (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 AHAs for Alpha Hydroxy Acids (glycolic acid, malic acid, mandelic acid), BHAs for Beta hydroxy acids (salicylic acid), or PHAs for Poly Hydroxy Acids (gluconolactone)... They produce a more or less gentle exfoliation: glycolic acid, smaller, penetrates more deeply, is ultra effective but can be irritating, when PHAs are much gentler but require more time to act. And promote skin renewal, unclogging of pores, a softer skin texture, better hydration...

• Enzymes: these enzymes (usually plant-based) “nibble” at the bonds 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 (desquamating) effect, but which can be irritating, particularly for sensitive skin. Hence the search for so-called "retinol-like" molecules of plant origin, which provide the same actions without the drawbacks, such as bakuchiol, harungana, sea fir, paillon bean, pelargonium essential oil. New, micronized mother-of-pearl powder introduced into facial care products has scientifically demonstrated that by inducing the expression of certain key proteins such as filaggrin, it stimulates the migration of keratinocytes to the surface of the epidermis to ensure the correct "turnover" of cell renewal which guarantees repair and regeneration of the barrier and the epidermis to maintain stronger, healthier and more 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, peppers, leafy green vegetables). Foods rich in vitamin C (citrus fruits, kiwi, peppers) are also useful for good cell regeneration. In the NACRE ÉCLAT Range from BLUE SKINCARE, 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 antioxidant and contributes to the normal formation of collagen for plumper skin.

Have a good nighttime routine

Cell renewal peaks at night. No longer having to defend themselves from daytime aggressions, skin cells repair and regenerate between 11 p.m. and 2 a.m. It is even around 1 a.m. that skin activity is at its peak, multiplying cell renewal by three compared to the same mechanism at 1 p.m. It is therefore time to give your skin a 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 is water-intensive. 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, getting 7 hours of sleep if possible to give the skin time to regenerate.