If you think your skin is just a surface to treat, or worse, an enemy to fight, it’s worth changing your perspective. The skin is a living, dynamic, and intelligent organ: it changes over time, responds to stimuli, and needs consistent care. It stands between you and the world, which is why it should be understood before it’s treated.
In this guide, you’ll find everything you need to understand how the skin is structured, how it works, and how to care for it: from anatomical basics to the pro-age philosophy. If you’re looking for practical basics instead — which steps you need and in what order — start with the article on skincare: what it means and where to start.
Article written by Elisa Avalle, founder of LeLang Skin Care and dermocosmetics specialist. Cover image generated with the help of artificial intelligence.
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A complex organ, not just a surface
The skin is the largest organ in the human body. It performs essential functions: mechanical and chemical protection, temperature regulation, hydration, sensory perception, and immune defense. It isn’t a static covering, but a tissue that renews itself, adapts, and communicates with the rest of the body.
Skin varies depending on the area: it’s thicker on the hands and feet, thinner on the face, and very thin around the eyes. That’s why every routine should take these structural differences into account — and why a face cream isn’t suitable for the eye area.
Not all skin is the same, and each skin type needs specific care. Whether you have one skin type or another depends on genetics, lifestyle, and hormonal balance. We discuss this in our article on different skin types.
How it’s structured: epidermis, dermis, and hypodermis
The L epidermis: the protective barrier
The outermost layer is the epidermis. This is where the skin barrier is found, the structure that keeps water in and external agents out.
Think of it as a wall: the bricks are the cells of the stratum corneum, and the mortar is a lipid matrix made up of ceramides, fatty acids, and cholesterol. When the barrier is intact, the skin retains water well; when it is compromised, it becomes dry, rough, and more sensitive.
The dermis: the supporting structure
Beneath the epidermis is the dermis, where the proteins that provide structure are found: collagen, which provides strength, and elastin, which allows the skin to return to its original shape. Hyaluronic acid is also found here, along with fibroblasts, the cells that produce all three substances.
The dermis also contains blood vessels and nerves. This is where loss of firmness occurs when collagen and elastin production decreases: it isn’t a defect, but a physiological process.
L’hypodermis: the cushion
The deepest layer, composed mainly of adipose tissue, protects against impacts and pressure, serves as an energy reserve and regulates temperature. Fat distribution changes over time and with hormones, contributing to the changes we observe in the face.
The fourth layer almost no one talks about: the epicutaneous mantle
There are three layers, but the outermost boundary with the outside world isn’t the stratum corneum. Above it is an ultra-thin film, the epicutaneous mantle, and that’s what we actually touch when we run a hand over our face.
It is an oil-in-water emulsion made from materials of different origins. The aqueous phase is sweat — 99% water, with dissolved mineral salts, urea, amino acids, lactic acid, citric acid and urocanic acid. The fatty phase comes from two sources that shouldn’t be confused: sebum produced by the sebaceous glands, and epidermal cholesterol, released by keratinocytes as they move toward the surface.
This second source explains something that causes a lot of confusion in cosmetics: cholesterol sulfate regulates desquamation. It isn’t residue; it’s a signal that determines when corneocytes detach. Flaky skin doesn’t necessarily need more oils on the surface: it may have a problem regulating cell shedding, which is something else entirely.
Why your pH returns to normal on its own after using soap
The water-soluble substances in the mantle - particularly the organic acids - give it a pH between 5 and 6 and, above all, strong buffering power. This is why, after using an alkaline cleanser, the skin quickly returns to its usual pH: it protects itself without needing products that "rebalance pH." The full picture is in the article on skin pH.
The real damage is something else. A highly degreasing cleanser does not alter pH over the long term: it removes the lipid-soluble fraction of the mantle, and without it, the stratum corneum is left exposed. This leads to tight-feeling skin and flaking after a shower. Under normal conditions, it restores itself quickly; if this happens every day, it does not have time.
There is another function that almost no one associates with this film: the urocanic acid in sweat absorbs some ultraviolet radiation. This is a minimal defense that in no way replaces sunscreen, but it tells us something about how the skin protects itself - and what is stripped away by improper cleansing.
The functions of the skin
- Defense: protects against mechanical agents, chemicals, microorganisms, and UV rays. The skin microbiota lives on the surface and helps keep the barrier strong.
- Water balance: healthy skin keeps transepidermal water loss low. When the barrier is damaged, skin becomes dry and flaky.
- Thermoregulation: through vasodilation, vasoconstriction, and sweating.
- Sensory perception: receptors that sense touch, pressure, temperature, and pain. This is also why the sensory experience of a cosmetic product is not a minor detail: it influences how consistently we use it.
- pH balance: the acid mantle, with a pH between 4.5 and 5.5, prevents pathogens from multiplying.
The skin barrier: the starting point
If the skin is a complex organ, the barrier is its starting point. A healthy barrier retains moisture, reduces reactivity and sensitivity, and allows active ingredients to work better without irritation.
That’s why every routine should start with respecting the skin barrier: gentle cleansers, non-harsh formulas, and supportive ingredients such as ceramides, physiological lipids, niacinamide, and hyaluronic acid. Caring for your skin doesn’t just mean adding active ingredients; first and foremost, it means preserving what’s already working.
How skin changes over time: the pro-age philosophy
Over the course of our lives, collagen and elastin production decreases, hyaluronic acid levels drop, and fibroblasts become less active. These are physiological processes, not flaws.
Some factors, however, accelerate it: unprotected sun exposure, pollution, stress, insufficient sleep, and overly harsh products. Cumulative damage from UV rays, or photoaging, causes more pronounced wrinkles, loss of firmness, and uneven skin tone.
Sun protection is the preventive measure with the strongest evidence: it blocks cumulative damage that accelerates collagen loss and promotes dark spots. It’s not optional; it’s the foundation of any pro-age routine.
Where anti-aging treats wrinkles and spots as flaws to eliminate, the pro-age approach accepts aging as a natural process and supports it with realistic goals: strengthen the skin barrier and hydration, use active ingredients that improve skin quality, and adapt your routine to your age.
Skin during menopause
There’s a time when the skin changes especially noticeably: menopause. Lower estrogen levels lead to reduced collagen and elastin production, a drop in hyaluronic acid, and drier, more reactive skin.
It’s not a fault, but a physiological consequence. The skin doesn’t become “wrong”: its characteristics change, and it needs different care. L’s goal isn’t to restore the skin you had in your thirties, but to help it function well in its new phase—as we explain in our skincare routine for skin over 50.
Neurocosmetics: the dialogue between skin and brain
There is a deep connection between the skin and the nervous system: both develop from the same embryonic layer. This dialogue is known as the brain-skin axis and is the basis of neurocosmetics.
Under stress, the brain releases cortisol, which disrupts the barrier, increases sebum production, and makes the skin more fragile. But communication goes both ways: the skin also communicates with the brain, and this is the principle behind neurocosmetics.
How to choose products
Start with cleansing
A cleanser that's too harsh strips away natural lipids and compromises the barrier. Choose products with a pH close to the skin's natural pH, free from harsh soaps and sulfates.
CLEANSING GENTLE OIL Makeup-removing facial cleansing oil non-comedogenic, the first step of double cleansing Dissolves makeup, including... Discover CLEANSING GENTLE OIL
Among the useful active ingredients during skin renewal is mandelic acid, which exfoliates without disrupting the barrier's balance.
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
Functional ingredients, not trends
A functional ingredient has a clear mechanism of action, is supported by research, and targets a specific function. Ceramides, hyaluronic acid, niacinamide, peptides, vitamin C, and urea all have a specific role. A few well-researched, well-tolerated active ingredients are best.
Changing your routine too often makes it harder to see the real effects and increases the risk of irritation. Stick to a stable routine for at least 4-8 weeks, observe how your skin responds, and make changes only if necessary. Consistency matters more than having the perfect product.
Frequently asked questions
What are the layers of the skin?
There are three: the epidermis, the outer layer where the skin barrier is located; the dermis, which contains collagen, elastin, hyaluronic acid, blood vessels, and nerves; and the hypodermis, the deep layer of fatty tissue. The epidermis is also covered by the hydrolipid film, a thin emulsion of sweat and lipids.
What is the skin barrier for?
It retains water in the skin and keeps external agents out. When intact, the skin remains hydrated and tolerates active ingredients better; when weakened, it becomes dry, rough, and more sensitive.
What is the normal pH of the skin?
The skin's surface has a slightly acidic pH of around 4.5 to 5.5. Thanks to the buffering capacity of the skin's surface film, healthy skin quickly restores its pH on its own, even after using an alkaline cleanser.
Why does skin change with age?
Over the years, collagen, elastin, and hyaluronic acid levels decrease, and fibroblasts become less active. This is a physiological process accelerated by the sun, stress, smoking, and insufficient sleep.
How long does it take to see the effects of a new routine?
At least four to eight weeks of consistent use. Changing products too often doesn't allow you to assess the results and increases the risk of irritation.
In conclusion
Understanding the structure and function of your skin is the first step to caring for it mindfully. There's no need to chase perfect skin: what matters is supporting its health, comfort, and function.
If you don't know where to start when it comes to your skin type, you can try our skin type quiz, or have your skin assessed in person at one of our LeLang partner pharmacies: the condition of the hydrolipidic film and the hydration level of the stratum corneum can't be assessed from a photo.
15-minute free consultation with the founder
If you're looking for practical support and don't know where to start, book a free virtual skincare consultation with Elisa Avalle, founder of LeLang.
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 Kligman A.M., The uses of sebum?, in The sebaceous glands, Advances in Biology of Skin vol. 4, Pergamon Press, Oxford, 1963, pp. 110-124
03 Proksch E., Brandner J.M., Jensen J.M., The skin: an indispensable barrier, Experimental Dermatology, 2008
On the website: skin types · the skin barrier · skin pH
