A cell is born at the bottom of the epidermis, moves upward toward the surface, dies along the way, and eventually sheds. It takes about thirty days, fourteen of which are spent in the stratum corneum.
It is happening right now, as you read, across the entire surface of your face. And most of the things we do to the skin interfere with this process, in one way or another.
Turnover is not "accelerated": it is supported or disrupted. It is a differentiation process with mandatory stages, and each one produces something the skin needs — including its own moisturizing factors. Forcing it does not make new cells reach the surface sooner: it makes unfinished cells reach the surface.
Article written by Elisa Avalle, founder of LeLang Skin Care and a dermocosmetics specialist. Cover image generated with the support of artificial intelligence.
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How long renewal really takes
Only the cells in the basal layer, the deepest layer of the epidermis, are capable of dividing. Each division produces two: one remains in place and immediately starts dividing again, while the other detaches and begins to move upward. From that moment on, it will never divide again — its role is different.
The time between the start of upward movement and shedding is the epidermal turnover time: on average, about 30 days, of which 14 are spent in the stratum corneum alone.
This fact has an immediate practical consequence, and it is why cosmetics always talks about four to eight weeks: before a routine can show an effect on the surface, at least one complete cycle must have passed. Anyone who changes products after ten days is not evaluating anything.
What happens to the cell as it moves upward
Moving upward is not a relocation but a transformation. The keratinocyte starts out cubic and voluminous and progressively flattens; new structures appear in the granular layer; when it reaches the stratum corneum, it has lost its nucleus and organelles. It has become a corneocyte: a dead, flat cell full of keratin.
Two of these structures deserve attention because they explain things we take for granted in cosmetics.
Keratohyalin granules and the origin of moisturizing factors
They contain a protein, profilaggrin. As it moves upward, it transforms into filaggrin, whose role is to aggregate the keratin filaments, holding them together like cement.
But the story does not end there. In the most superficial layers, filaggrin is itself broken down by enzymes, and the resulting fragments — amino acids, pyrrolidone carboxylic acid, urea, citrate — are what we call the Natural Moisturizing Factor.
This changes how we read a label. The urea in a cream is not a foreign substance added to the skin: it is the same molecule that the skin produces on its own, at the end of its renewal cycle. Applying it is not a trick, but replenishment — and this explains why it works so well on skin in which that cycle is disrupted. I discuss this in detail in the article on urea and biomimetic hydration.
Genetics provides confirmation: mutations in the gene encoding filaggrin alter barrier function and are a major predisposing factor for atopic dermatitis and ichthyosis vulgaris, conditions in which transepidermal water loss also increases. Less filaggrin means less cement between the filaments and fewer moisturizing factors at the end of the process.
Odland bodies, which prepare the shedding process
They release their contents into the spaces between cells, and these consist of two things: the lipids that form the intercellular cement — the mortar between the bricks of the skin barrier — and the enzymes that govern desquamation.
In other words, the skin produces its own exfoliants. It does not lack the mechanism; it may lack the conditions needed for it to work.
Why we don't see the skin flaking
Under normal conditions, desquamation is invisible because cells detach one at a time or in small groups of three or four. It becomes visible only when cohesion between corneocytes increases and the groups become large enough to form scales.
Behind the shedding lies a precise chemical change: cholesterol sulfate predominates in the compact layer, while free cholesterol predominates in the superficial layer. This transformation loosens the bonds between cells and allows natural shedding.
This leads to a counterintuitive point: skin that is shedding does not necessarily need more oils. It may have a problem regulating shedding. It is one of the three criteria used to truly describe a skin type, independent of its water and lipid content — I explain this in the article on different skin types.
What slows turnover
- Age: it is the main factor. The cycle progressively lengthens, and corneocytes remain adhered for longer.
- Dehydration of the stratum corneum: desquamation enzymes work in a watery environment. On a water-deprived surface, they slow down, and shedding becomes irregular.
- Sun damage: chronic exposure thickens the stratum corneum and alters its turnover.
- A compromised barrier: when the lipid component is lacking, the part of the mechanism entrusted to Odland bodies also breaks down.
The visible result is always the same: uneven surface, rough texture, dull complexion. It is one of the four mechanisms behind dull skin, and the one that responds fastest.
What you can really do
Exfoliate moderately, not more
Chemical and enzymatic exfoliation work on the adhesion between corneocytes, meaning they help with the final step of a process that is already underway. Once or twice a week: beyond that threshold, nothing speeds up, the stratum corneum becomes thinner, and tissue that has not completed differentiation is brought to the surface.
Among the acids, mandelic acid has a larger molecule than glycolic acid and penetrates more slowly, making it better tolerated. The comparison between the acid families is in the exfoliating acids guide, while the practical steps are explained in how to exfoliate your skin.
MANDELIC ENZYMATIC SOFT PEEL Mandelic Acid and Enzymatic Facial Peel Highly tolerated, gentle exfoliant that stimulates cell turnover. Removes de... Discover MANDELIC ENZYMATIC SOFT PEEL
Keeping the stratum corneum hydrated
This is the aspect that almost no one associates with turnover, and it may be the most important: without water, the enzymes involved in desquamation cannot work. Hydrating does more than make the skin feel softer; it enables the mechanism that renews it to function.
HYALURONIC ADVANCE Plumping face cream with hyaluronic acid, filler effect Multiple hyaluronic acid: hydrates from deep within to the s... Discover HYALURONIC ADVANCE
If the sensation of tight skin returns as soon as you skip an application, the problem is hydration, not turnover: the distinction is explained in dry or dehydrated skin.
Protecting against the sun
Cumulative sun damage permanently alters turnover. It is the measure with the longest-lasting effect and the one most often neglected.
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The treatments that target this area are collected in the facial exfoliants collection.
Determining whether uneven texture is due to slowed turnover, dehydration, or a compromised barrier cannot be done by eye: these are three similar-looking situations that require different approaches. It is an assessment best done in person, and at LeLang partner pharmacies, a pharmacist can carry it out with you.
Free 15-minute consultation with the founder
If your skin remains rough and dull despite your routine, we can look together at where the renewal process is getting stuck: book a free virtual skincare consultation with Elisa Avalle, founder of LeLang.
Frequently asked questions
How often does facial skin renew itself?
On average, about every thirty days, counting from when the cell leaves the basal layer until it is shed. Fourteen of those days are spent in the stratum corneum alone. The time gradually increases with age.
Can cell turnover be accelerated?
You can encourage the detachment of cells that are already ready, and this produces a visible effect quickly. You cannot, however, speed up differentiation: it is a sequence of biochemical stages with their own timing, and forcing it brings immature cells to the surface. The surface becomes more fragile, not younger.
Why does the skin look brighter for only a few days after exfoliation?
Because what was ready to detach was removed; the production rate upstream was not changed. The effect lasts until the new layer reaches the surface. This is why consistency matters more than the intensity of a single treatment.
Is turnover the same throughout the body?
No. The thickness of the epidermis and the rate of cell turnover vary greatly from one area to another: the face and eye contour do not behave like the hands or the sole of the foot. This is one reason why body products cannot automatically be used on the face.
Is visible flaking always a problem?
When scales are visible, it means that cohesion between corneocytes has increased: the cells detach in large groups instead of three or four at a time. If this persists and is accompanied by intense itching, marked redness, or lesions, the condition should be assessed by a dermatologist: some scaly conditions are dermatological and cannot be resolved with a cosmetic product.
Sources for this article
01 Jackson S.M., Williams M.L., Feingold K.R., Elias P.M., Pathobiology of the stratum corneum, Western Journal of Medicine, 158, March 1993, pp. 279-285
02 Palmer C.N.A. et al., Common loss-of-function variants of the epidermal barrier protein filaggrin are a major predisposing factor for atopic dermatitis, Nature Genetics, vol. 38 no. 4, April 2006, pp. 441-446
03 Rawlings A.V., Harding C.R., Moisturization and skin barrier function, Dermatologic Therapy, 2004
04 Proksch E., Brandner J.M., Jensen J.M., The skin: an indispensable barrier, Experimental Dermatology, 2008
On the website: how to exfoliate the skin · urea and biomimetic hydration · the skin barrier · facial exfoliants
