Skin cell turnover

The body is in a constant state of renewal throughout our lives. Virtually all of our organs, except the neurones and heart cells, get replaced completely several times over at different paces. The renewal timelines range from one week for the liver to four months for the bones. The skin, which is an organ, also gets replaced thanks to cell regeneration.
Cell turnover refers to the cells’ ability to reproduce, i.e. to produce genetically identical cells that take the place of other cells. When their lives are at an end, these cells self-destruct. Skin cell turnover is the process that leads to the shedding of thousands of dead cells every day, which get replaced by new ones. The right cell turnover pace, neither too slow nor too fast, is essential to maintain good barrier function for glowingly even, smooth skin full of energy.

Where does skin cell turnover take place?

The epidermis (the surface layer of the skin) is a bit like a game of Tetris. It is a sort of wall made up of bricks (keratinocytes), which are cells that are constantly rising towards the surface. These “brick cells” originate in the basal layer, at the bottom of the epidermis, and gradually migrate towards the stratus corneum (the most superficial of the epidermal layers).

What is the mechanism of skin cell turnover?

As they move up from the deep (basal) layer of the epidermis towards the surface, keratinocytes go through various changes. This is called cellular differentiation.

• Keratinocyte stem cells are found in the reservoirs of the basal layer. They each divide, creating a daughter stem cell - which will take their place in the basal layer and itself divide later - and a further keratinocyte. This is almost cubic in shape and has a nucleus. Pushed upwards by the new cells, it begins its differentiation by moving up to the next level. This is called cell proliferation.
• The stratum spinosum is the thickest layer of the epidermis, made up of four or five layers of keratinocytes. These are almost polyhedral in shape, filled with water and bonded together by desmosomes, hydrophilic and hydrophobic substances. As they rise, they get loaded up with keratin and melanin.
• The main transformation, called cell differentiation, takes place in the stratum granulosum. This is a transition zone that separates the live epidermal layers from the so-called "dead" layers of the stratum corneum. The keratinocytes get completely remodelled into corneocytes. They each gradually lose their nucleus and plasma membrane, which give way to a rigid insoluble envelope (the cornified envelope). Incidentally, filaggrin, one of the differentiation markers, gets turned into free amino acids which make up the "natural moisturising factors" of the stratum corneum.
• By the time the corneocytes reach the surface, in the stratum corneum, they are flat and filled with keratin. They clump together in a stack of cell lamellae bonded together by intercellular cement made of lipids, to form the skin barrier. They eventually detach, due to enzymes that pop off the “press studs” holding the corneocytes together (the desmosomes). This is called desquamation.

All of this happens slowly and almost invisibly. Without realising it, we shed about four grams of skin per day.

What factors affect cell turnover?

In a healthy epidermis, the amount of cells shed from the surface is offset by the production of an equal amount of new keratinocytes. But sometimes the process can go wrong, with slowed or accelerated proliferation.

• Accelerated turnover - scarring and psoriasis

When the skin is damaged or infected, cell turnover increases to heal the wound - this is the healing process - or to fight the infection with new cells. This acceleration can reach up to seven times the normal cell reproduction rate (i.e. a timeline of three to four days).

Psoriasis is a chronic inflammatory skin condition, considered an autoimmune disease, which presents as accelerated cell turnover in the affected area (knees, elbows, scalp, etc.), which goes on unchecked. New cells emerge and rise to the surface at a pace overtaking that of desquamation. The dead cells build up on the surface of the skin and end up forming patches, or "scales". These flake off, as scales do. Meanwhile, the cells beneath jostle each other and pile up, causing painful lesions that may bleed.

• Slow turnover

Stress, obesity, smoking, pollution, UV rays and advancing age slow down skin turnover. The skin struggles to shed itself, and dead cells build up on the surface because the bonds that hold skin cells together (desmosomes) don’t break down as they should. These form a kind of film, which thickens the skin and makes the complexion look sallow and rough. This build-up also causes a loss of cohesion in the corneocytes, which are no longer able to regulate water evaporation effectively. This results in gradual dehydration and the premature appearance of fine lines.

How do you encourage skin cell turnover?

To « boost » cell turnover there are several options, which are not mutually exclusive.

That’s why so-called chemical or enzyme peels are often recommended – all the more for sensitive skin – as they make for even exfoliation via chemical breakdown of the cells. There are two types:

• Acids: these are the AHAs (Alpha Hydroxy Acids) that we hear so much about (glycolic acid and malic acid), BHAs (Beta Hydroxy Acids) (salicylic acid), or PHAs (Poly Hydroxy Acids) (gluconolactone), and so on. They exfoliate with varying degrees of gentleness. Glycolic acid, whose molecules are smaller, penetrates more deeply and is highly effective, but can irritate the skin. Whereas PHAs are much gentler but take longer to work. And they promote skin turnover, pore unclogging, softer skin texture, better hydration, etc.

• Enzymes: these (generally plant-based) enzymes "nibble" at the bonds between dead cells (the desmosomes) to loosen them without damaging live cells or irritating the skin.

Eat right

Diet also influences cell turnover. So favour foods high in vitamin A and beta-carotene. Vitamin A is mainly found in animal products (eggs, butter, offal and liver). Beta-carotene, which is a precursor of vitamin A and also a powerful antioxidant, is found in orange fruits and vegetables (carrots, sweet potatoes, melons, peppers and green leafy vegetables). Foods high in vitamin C (citrus fruits, kiwi fruit and peppers) also play a part in proper cell regeneration.

If your skin is tired and lacks radiance, we recommend rounding off your skin-enhancing regimen with the Skin-Perfecting Food Supplement in the Nacre Éclat range from BLUE SKINCARE. Highly concentrated in active nacre, it also contains a pre- and probiotic complex to rebalance the intestinal microbiota, and hyaluronic acid to maintain the skin's hydration and elasticity. High in vitamin C and zinc, it is antioxidant and supports normal collagen formation for plumper skin.

Embrace a good night-time routine

Cell turnover is at its highest at night. Since the skin cells no longer have to defend themselves against daytime external damaging factors, they repair and regenerate themselves between 11p.m. and 2 a.m. The skin's activity even reaches its peak at around 1a.m., tripling cell turnover compared to that at 1pm.

So that’s the time to use a specific skincare product that helps cell turnover along, such as BLUE SKINCARE Nacre Éclat Skin Renewal Serum, which is highly concentrated in active nacre powder, NACR-45^®.

If the skin is dehydrated, that needs to be addressed because the skin turnover process takes a lot of water. So proper hydration, achieved through skincare but also by drinking 1.5 litres of water per day, is essential to support cell regeneration.

Obviously, it’s essential to get a good night's sleep. Get seven hours in if possible, to give the skin time to regenerate.